diff --git a/.github/workflows/hw5-ci.yml b/.github/workflows/hw5-ci.yml
new file mode 100644
index 00000000..03fc8f77
--- /dev/null
+++ b/.github/workflows/hw5-ci.yml
@@ -0,0 +1,57 @@
+name: Python CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        python-version: [3.11, 3.13]
+
+    defaults:
+      run:
+        working-directory: hw5
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v3
+
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
+        pip install pytest pytest-cov fastapi uvicorn httpx
+
+    - name: Set PYTHONPATH
+      run: echo "PYTHONPATH=$PWD" >> $GITHUB_ENV
+
+    - name: Run tests with coverage
+      run: |
+        pytest --cov=shop_api \
+               --cov-report=term-missing \
+               --cov-report=xml \
+               --cov-report=html \
+               tests/
+
+    - name: Upload coverage XML
+      uses: actions/upload-artifact@v4
+      with:
+        name: coverage-xml
+        path: coverage.xml
+
+    - name: Upload coverage HTML
+      uses: actions/upload-artifact@v4
+      with:
+        name: coverage-html
+        path: htmlcov/
diff --git a/hw1/app.py b/hw1/app.py
index 6107b870..0322e89c 100644
--- a/hw1/app.py
+++ b/hw1/app.py
@@ -1,5 +1,8 @@
 from typing import Any, Awaitable, Callable
+from urllib.parse import parse_qs
+import json
 
+from utils import fibonacci, factorial, mean
 
 async def application(
     scope: dict[str, Any],
@@ -12,7 +15,92 @@ async def application(
         receive: Корутина для получения сообщений от клиента
         send: Корутина для отправки сообщений клиенту
     """
-    # TODO: Ваша реализация здесь
+    if scope.get("type") == "lifespan":
+        while True:
+            message = await receive()
+            if message.get("type") == "lifespan.startup":
+                await send({"type": "lifespan.startup.complete"})
+            elif message.get("type") == "lifespan.shutdown":
+                await send({"type": "lifespan.shutdown.complete"})
+                return
+
+    path = scope["path"]
+    query = parse_qs(scope["query_string"].decode())
+    method = scope.get("method", "GET")
+
+    def json_response(data: dict, status_code: int = 200):
+        return json.dumps(data).encode(), b"application/json", status_code
+
+    if path == "/factorial" and method == "GET":
+        n_raw = query.get("n", [None])[0]
+        if not n_raw:
+            body, content_type, status = json_response({"detail": "Missing or empty 'n' parameter"}, 422)
+        else:
+            try:
+                n = int(n_raw)
+            except Exception:
+                body, content_type, status = json_response({"detail": "'n' must be an integer"}, 422)
+            else:
+                if n < 0:
+                    body, content_type, status = json_response({"detail": "'n' must be >= 0"}, 400)
+                else:
+                    body, content_type, status = json_response({"result": factorial(n)})
+
+    elif path.startswith("/fibonacci") and method == "GET":
+        parts = path.split("/")
+        n_raw = parts[2] if len(parts) > 2 else ""
+        if not n_raw:
+            body, content_type, status = json_response({"detail": "Missing or empty n parameter"}, 422)
+        else:
+            try:
+                n = int(n_raw)
+            except Exception:
+                body, content_type, status = json_response({"detail": "n must be integer"}, 422)
+            else:
+                if n < 0:
+                    body, content_type, status = json_response({"detail": "n must be >= 0"}, 400)
+                else:
+                    body, content_type, status = json_response({"result": fibonacci(n)})
+
+    elif path == "/mean" and method == "GET":
+        raw_body = scope.get("body", b"")
+        while True:
+            message = await receive()
+            if message["type"] == "http.request":
+                raw_body += message.get("body", b"")
+                if not message.get("more_body", False):
+                    break
+        try:
+            body_data = json.loads(raw_body.decode()) if raw_body else None
+        except Exception:
+            body_data = None
+
+        if body_data is None:
+            body, content_type, status = json_response({"detail": "Missing or invalid body"}, 422)
+        elif not isinstance(body_data, list) or not body_data:
+            body, content_type, status = json_response({"detail": "Body must be non-empty list"}, 400)
+        else:
+            try:
+                numbers = [float(x) for x in body_data]
+            except Exception:
+                body, content_type, status = json_response({"detail": "All elements must be numbers"}, 400)
+            else:
+                body, content_type, status = json_response({"result": mean(",".join(str(x) for x in numbers))})
+
+    else:
+        body, content_type, status = json_response({"detail": "Not Found"}, 404)
+
+    await send({
+        "type": "http.response.start",
+        "status": status,
+        "headers": [[b"content-type", content_type]]
+    })
+
+    await send({
+        "type": "http.response.body",
+        "body": body
+    })
+
 
 if __name__ == "__main__":
     import uvicorn
diff --git a/hw1/utils.py b/hw1/utils.py
new file mode 100644
index 00000000..de73f266
--- /dev/null
+++ b/hw1/utils.py
@@ -0,0 +1,19 @@
+def fibonacci(n):
+    n = int(n)
+    if n <= 0:
+        return []
+    seq = [0, 1]
+    for _ in range(2, n):
+        seq.append(seq[-1] + seq[-2])
+    return seq[:n]
+
+def factorial(n):
+    n = int(n)
+    result = 1
+    for i in range(2, n+1):
+        result *= i
+    return result
+
+def mean(numbers):
+    numbers = [float(x) for x in numbers.split(",")]
+    return sum(numbers) / len(numbers)
\ No newline at end of file
diff --git a/hw2/hw/shop_api/main.py b/hw2/hw/shop_api/main.py
index f60a8c60..952e76fc 100644
--- a/hw2/hw/shop_api/main.py
+++ b/hw2/hw/shop_api/main.py
@@ -1,3 +1,9 @@
 from fastapi import FastAPI
+from shop_api.routers import items, carts, chat
+
 
 app = FastAPI(title="Shop API")
+
+app.include_router(items.router)
+app.include_router(carts.router)
+app.include_router(chat.router)
\ No newline at end of file
diff --git a/hw2/hw/shop_api/models/__init__.py b/hw2/hw/shop_api/models/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/routers/__init__.py b/hw2/hw/shop_api/routers/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/routers/carts.py b/hw2/hw/shop_api/routers/carts.py
new file mode 100644
index 00000000..39a179be
--- /dev/null
+++ b/hw2/hw/shop_api/routers/carts.py
@@ -0,0 +1,58 @@
+from fastapi import APIRouter, HTTPException, Query, Path, Response
+from shop_api.schemas.cart import Cart
+from shop_api.utils.cart_utils import compute_cart
+from shop_api.storage.memory import _carts, _items, _lock, _next_cart_id
+from typing import Optional, List
+
+
+router = APIRouter(prefix="/cart", tags=["carts"])
+
+@router.post("/", status_code=201)
+def create_cart(response: Response):
+    global _next_cart_id
+    with _lock:
+        cid = _next_cart_id
+        _next_cart_id += 1
+        _carts[cid] = {}
+    response.headers["Location"] = f"/cart/{cid}"
+    return {"id": cid}
+
+@router.get("/{id}", response_model=Cart)
+def get_cart(id: int = Path(..., gt=0)):
+    try:
+        return compute_cart(id)
+    except KeyError:
+        raise HTTPException(status_code=404, detail="cart not found")
+
+@router.get("/", response_model=List[Cart])
+def list_carts(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    min_quantity: Optional[int] = Query(None, ge=0),
+    max_quantity: Optional[int] = Query(None, ge=0),
+):
+    carts = []
+    for cid in sorted(_carts.keys()):
+        cart = compute_cart(cid)
+        total_qty = sum(i.quantity for i in cart.items)
+        if min_quantity is not None and total_qty < min_quantity:
+            continue
+        if max_quantity is not None and total_qty > max_quantity:
+            continue
+        if min_price is not None and cart.price < min_price:
+            continue
+        if max_price is not None and cart.price > max_price:
+            continue
+        carts.append(cart)
+    return carts[offset: offset + limit]
+
+@router.post("/{cart_id}/add/{item_id}", response_model=Cart)
+def add_item(cart_id: int, item_id: int):
+    if cart_id not in _carts:
+        raise HTTPException(status_code=404, detail="cart not found")
+    if item_id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    _carts[cart_id][item_id] = _carts[cart_id].get(item_id, 0) + 1
+    return compute_cart(cart_id)
diff --git a/hw2/hw/shop_api/routers/chat.py b/hw2/hw/shop_api/routers/chat.py
new file mode 100644
index 00000000..0dcf6da9
--- /dev/null
+++ b/hw2/hw/shop_api/routers/chat.py
@@ -0,0 +1,30 @@
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+from collections import defaultdict
+import random
+import string
+from typing import Dict, List
+
+router = APIRouter(prefix="/chat", tags=["chat"])
+
+chat_rooms: Dict[str, List[WebSocket]] = defaultdict(list)
+usernames: Dict[WebSocket, str] = {}
+
+def random_username() -> str:
+    return ''.join(random.choices(string.ascii_letters + string.digits, k=8))
+
+@router.websocket("/{chat_name}")
+async def websocket_chat(websocket: WebSocket, chat_name: str):
+    await websocket.accept()
+    username = random_username()
+    usernames[websocket] = username
+    chat_rooms[chat_name].append(websocket)
+    try:
+        while True:
+            data = await websocket.receive_text()
+            message = f"{username} :: {data}"
+            for ws in chat_rooms[chat_name]:
+                if ws != websocket:
+                    await ws.send_text(message)
+    except WebSocketDisconnect:
+        chat_rooms[chat_name].remove(websocket)
+        del usernames[websocket]
diff --git a/hw2/hw/shop_api/routers/items.py b/hw2/hw/shop_api/routers/items.py
new file mode 100644
index 00000000..3942bd8b
--- /dev/null
+++ b/hw2/hw/shop_api/routers/items.py
@@ -0,0 +1,81 @@
+from fastapi import APIRouter, HTTPException, Query, Response
+from shop_api.schemas.item import Item, ItemCreate
+from shop_api.storage.memory import _items, _lock, _next_item_id
+from typing import Optional, List
+
+
+router = APIRouter(prefix="/item", tags=["items"])
+
+@router.post("/", response_model=Item, status_code=201)
+def create_item(item: ItemCreate):
+    global _next_item_id
+    with _lock:
+        iid = _next_item_id
+        _next_item_id += 1
+        new_item = Item(id=iid, name=item.name, price=item.price)
+        _items[iid] = new_item
+    return new_item
+
+@router.get("/{id}", response_model=Item)
+def get_item(id: int):
+    item = _items.get(id)
+    if not item or item.deleted:
+        raise HTTPException(status_code=404, detail="item not found")
+    return item
+
+@router.get("/", response_model=List[Item])
+def list_items(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    show_deleted: bool = Query(False),
+):
+    items = []
+    for it in _items.values():
+        if not show_deleted and it.deleted:
+            continue
+        if min_price is not None and it.price < min_price:
+            continue
+        if max_price is not None and it.price > max_price:
+            continue
+        items.append(it)
+    return items[offset: offset + limit]
+
+@router.put("/{id}", response_model=Item)
+def replace_item(id: int, item: ItemCreate):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    existing = _items[id]
+    existing.name = item.name
+    existing.price = item.price
+    _items[id] = existing
+    return existing
+
+@router.patch("/{id}", response_model=Item)
+def patch_item(id: int, patch: dict):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    item = _items[id]
+    if item.deleted:
+        return Response(status_code=304)
+    allowed_keys = {"name", "price"}
+    if not set(patch.keys()).issubset(allowed_keys):
+        raise HTTPException(status_code=422)
+    if "price" in patch:
+        price = patch["price"]
+        if price is not None and price < 0:
+            raise HTTPException(status_code=422)
+        item.price = price
+    if "name" in patch:
+        item.name = patch["name"]
+    _items[id] = item
+    return item
+
+@router.delete("/{id}")
+def delete_item(id: int):
+    item = _items.get(id)
+    if not item:
+        return {"status": "ok"}
+    item.deleted = True
+    return {"status": "ok"}
\ No newline at end of file
diff --git a/hw2/hw/shop_api/schemas/__init__.py b/hw2/hw/shop_api/schemas/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/schemas/cart.py b/hw2/hw/shop_api/schemas/cart.py
new file mode 100644
index 00000000..4e3ed90c
--- /dev/null
+++ b/hw2/hw/shop_api/schemas/cart.py
@@ -0,0 +1,14 @@
+from pydantic import BaseModel
+from typing import List
+
+
+class CartItem(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+class Cart(BaseModel):
+    id: int
+    items: List[CartItem]
+    price: float
\ No newline at end of file
diff --git a/hw2/hw/shop_api/schemas/item.py b/hw2/hw/shop_api/schemas/item.py
new file mode 100644
index 00000000..53021cde
--- /dev/null
+++ b/hw2/hw/shop_api/schemas/item.py
@@ -0,0 +1,18 @@
+from pydantic import BaseModel, Field
+from typing import Optional
+
+
+class ItemBase(BaseModel):
+    name: str
+    price: float = Field(..., ge=0)
+
+class ItemCreate(ItemBase):
+    pass
+
+class Item(ItemBase):
+    id: int
+    deleted: bool = False
+
+class ItemPatch(BaseModel):
+    name: Optional[str]
+    price: Optional[float]
\ No newline at end of file
diff --git a/hw2/hw/shop_api/storage/__init__.py b/hw2/hw/shop_api/storage/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/storage/memory.py b/hw2/hw/shop_api/storage/memory.py
new file mode 100644
index 00000000..e769f81d
--- /dev/null
+++ b/hw2/hw/shop_api/storage/memory.py
@@ -0,0 +1,9 @@
+from typing import Dict
+from threading import Lock
+from shop_api.schemas.item import Item
+
+_items: Dict[int, Item] = {}
+_carts: Dict[int, Dict[int, int]] = {}
+_next_item_id = 1
+_next_cart_id = 1
+_lock = Lock()
diff --git a/hw2/hw/shop_api/utils/cart_utils.py b/hw2/hw/shop_api/utils/cart_utils.py
new file mode 100644
index 00000000..b0c65c2e
--- /dev/null
+++ b/hw2/hw/shop_api/utils/cart_utils.py
@@ -0,0 +1,20 @@
+from shop_api.schemas.cart import Cart, CartItem
+from shop_api.storage.memory import _carts, _items
+
+
+def compute_cart(cart_id: int) -> Cart:
+    if cart_id not in _carts:
+        raise KeyError
+    bag = _carts[cart_id]
+    items_out = []
+    total = 0.0
+    for iid, qty in bag.items():
+        item = _items.get(iid)
+        if item is None:
+            name, available = "", False
+        else:
+            name, available = item.name, not item.deleted
+        items_out.append(CartItem(id=iid, name=name, quantity=qty, available=available))
+        if item and not item.deleted:
+            total += item.price * qty
+    return Cart(id=cart_id, items=items_out, price=total)
\ No newline at end of file
diff --git a/hw2/hw/websocket_test.py b/hw2/hw/websocket_test.py
new file mode 100644
index 00000000..2f14a519
--- /dev/null
+++ b/hw2/hw/websocket_test.py
@@ -0,0 +1,40 @@
+from fastapi.testclient import TestClient
+from shop_api.main import app
+import threading
+
+client = TestClient(app)
+
+
+def test_chat_broadcast():
+    with (
+        client.websocket_connect("/chat/testroom") as ws1,
+        client.websocket_connect("/chat/testroom") as ws2
+    ):
+        ws1.send_text("Hello world!")
+        message = ws2.receive_text()
+
+        assert "Hello world!" in message
+        assert "::" in message
+
+
+def test_chat_isolation_between_rooms():
+    with (
+        client.websocket_connect("/chat/testroom") as ws1,
+        client.websocket_connect("/chat/anotherroom") as ws2
+    ):
+        ws1.send_text("Message to room1")
+
+        received = []
+
+        def try_receive():
+            try:
+                msg = ws2.receive_text()
+                received.append(msg)
+            except Exception:
+                pass
+
+        t = threading.Thread(target=try_receive, daemon=True)
+        t.start()
+        t.join(timeout=0.5)
+
+        assert not received
diff --git a/hw3/Dockerfile b/hw3/Dockerfile
new file mode 100644
index 00000000..f08e675f
--- /dev/null
+++ b/hw3/Dockerfile
@@ -0,0 +1,13 @@
+FROM python:3.11-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+EXPOSE 8000
+
+CMD ["uvicorn", "shop_api.main:app", "--host", "0.0.0.0", "--port", "8000"]
diff --git a/hw3/README.md b/hw3/README.md
new file mode 100644
index 00000000..33cd5544
--- /dev/null
+++ b/hw3/README.md
@@ -0,0 +1,8 @@
+### Grafana + Prometheus
+![Tech Dashboard](./pics/tech_dashboard.jpg)
+
+![Business Dashboard](./pics/business_dashboard.jpg)
+
+### Запуск:
+```bash
+docker-compose up --build
diff --git a/hw3/docker-compose.yml b/hw3/docker-compose.yml
new file mode 100644
index 00000000..695d209d
--- /dev/null
+++ b/hw3/docker-compose.yml
@@ -0,0 +1,37 @@
+version: "3.9"
+
+services:
+  app:
+    build: .
+    container_name: shop_api
+    ports:
+      - "8000:8000"
+    networks:
+      - shopnet
+
+  prometheus:
+    image: prom/prometheus:latest
+    container_name: prometheus
+    ports:
+      - "9090:9090"
+    volumes:
+      - ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml:ro
+    networks:
+      - shopnet
+
+  grafana:
+    image: grafana/grafana:latest
+    container_name: grafana
+    environment:
+      - GF_SECURITY_ADMIN_PASSWORD=admin
+      - GF_SECURITY_ADMIN_USER=admin
+    ports:
+      - "3000:3000"
+    volumes:
+      - ./grafana/provisioning:/etc/grafana/provisioning
+    networks:
+      - shopnet   
+
+networks:
+  shopnet:
+    driver: bridge
diff --git a/hw3/grafana/provisioning/dashboards/dashboard.yml b/hw3/grafana/provisioning/dashboards/dashboard.yml
new file mode 100644
index 00000000..472a2279
--- /dev/null
+++ b/hw3/grafana/provisioning/dashboards/dashboard.yml
@@ -0,0 +1,11 @@
+apiVersion: 1
+
+providers:
+  - name: "Shop API Technical"
+    folder: "Tech"
+    options:
+      path: /etc/grafana/provisioning/dashboards
+  - name: "Shop API Business"
+    folder: "Business"
+    options:
+      path: /etc/grafana/provisioning/dashboards
diff --git a/hw3/grafana/provisioning/dashboards/shop_api_business_dashboard.json b/hw3/grafana/provisioning/dashboards/shop_api_business_dashboard.json
new file mode 100644
index 00000000..794d4643
--- /dev/null
+++ b/hw3/grafana/provisioning/dashboards/shop_api_business_dashboard.json
@@ -0,0 +1,334 @@
+{
+  "annotations": {
+    "list": [
+      {
+        "builtIn": 1,
+        "datasource": {
+          "type": "grafana",
+          "uid": "-- Grafana --"
+        },
+        "enable": true,
+        "hide": true,
+        "iconColor": "rgba(0, 211, 255, 1)",
+        "name": "Annotations & Alerts",
+        "type": "dashboard"
+      }
+    ]
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": 4,
+  "links": [],
+  "panels": [
+    {
+      "datasource": {
+        "type": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 15,
+        "x": 0,
+        "y": 0
+      },
+      "id": 3,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "editorMode": "code",
+          "expr": "rate(shop_carts_created_total[1m])",
+          "legendFormat": "Carts per minute",
+          "range": true,
+          "refId": "A"
+        }
+      ],
+      "title": "Carts Created per Minute",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 8,
+        "x": 15,
+        "y": 0
+      },
+      "id": 2,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "percentChangeColorMode": "standard",
+        "reduceOptions": {
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": "",
+          "values": false
+        },
+        "showPercentChange": false,
+        "textMode": "auto",
+        "wideLayout": true
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "count(shop_ws_connections)",
+          "refId": "A"
+        }
+      ],
+      "title": "Active Chat Rooms",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 15,
+        "x": 0,
+        "y": 6
+      },
+      "id": 4,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "sum(rate(shop_ws_messages_total[1m])) by (chat_name)",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Chat Messages per Minute",
+      "type": "timeseries"
+    },
+    {
+      "fieldConfig": {
+        "defaults": {
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 8,
+        "x": 15,
+        "y": 6
+      },
+      "id": 1,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "percentChangeColorMode": "standard",
+        "reduceOptions": {
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": "",
+          "values": false
+        },
+        "showPercentChange": false,
+        "textMode": "auto",
+        "wideLayout": true
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "sum(shop_items_total)",
+          "refId": "A"
+        }
+      ],
+      "title": "Total Items in Stock",
+      "type": "stat"
+    }
+  ],
+  "preload": false,
+  "refresh": "",
+  "schemaVersion": 42,
+  "tags": [],
+  "templating": {
+    "list": []
+  },
+  "timepicker": {},
+  "timezone": "browser",
+  "title": "Business Metrics",
+  "uid": "440d983f-0b3d-4579-b85d-3ee2dad1babd",
+  "version": 2
+}
\ No newline at end of file
diff --git a/hw3/grafana/provisioning/dashboards/shop_api_dashboard.json b/hw3/grafana/provisioning/dashboards/shop_api_dashboard.json
new file mode 100644
index 00000000..5779d8e0
--- /dev/null
+++ b/hw3/grafana/provisioning/dashboards/shop_api_dashboard.json
@@ -0,0 +1,408 @@
+{
+  "annotations": {
+    "list": [
+      {
+        "builtIn": 1,
+        "datasource": {
+          "type": "grafana",
+          "uid": "-- Grafana --"
+        },
+        "enable": true,
+        "hide": true,
+        "iconColor": "rgba(0, 211, 255, 1)",
+        "name": "Annotations & Alerts",
+        "type": "dashboard"
+      }
+    ]
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": 1,
+  "links": [],
+  "panels": [
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 0,
+        "y": 0
+      },
+      "id": 1,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "editorMode": "code",
+          "exemplar": false,
+          "expr": "sum(rate(http_requests_total[1m])) by (method, handler)",
+          "legendFormat": "{{method}} {{handler}}",
+          "range": true,
+          "refId": "A"
+        }
+      ],
+      "title": "HTTP Requests per Second",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 12,
+        "y": 0
+      },
+      "id": 2,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket[5m])) by (le))",
+          "legendFormat": "p95",
+          "refId": "A"
+        }
+      ],
+      "title": "Request Duration (p95)",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 12,
+        "x": 0,
+        "y": 7
+      },
+      "id": 3,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "shop_ws_connections",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Active WebSocket Connections",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 12,
+        "x": 12,
+        "y": 7
+      },
+      "id": 4,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "increase(shop_ws_messages_total[5m])",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "WebSocket Messages Sent",
+      "type": "timeseries"
+    }
+  ],
+  "preload": false,
+  "refresh": "",
+  "schemaVersion": 42,
+  "tags": [],
+  "templating": {
+    "list": []
+  },
+  "timepicker": {},
+  "timezone": "browser",
+  "title": "Shop API Dashboard",
+  "uid": "ecd408fb-c57c-4ba2-8452-260e76f954ed",
+  "version": 3
+}
\ No newline at end of file
diff --git a/hw3/grafana/provisioning/datasources/datasource.yml b/hw3/grafana/provisioning/datasources/datasource.yml
new file mode 100644
index 00000000..7285dbe4
--- /dev/null
+++ b/hw3/grafana/provisioning/datasources/datasource.yml
@@ -0,0 +1,11 @@
+apiVersion: 1
+
+datasources:
+  - name: Prometheus
+    type: prometheus
+    access: proxy
+    orgId: 1
+    uid: prometheus_ds
+    url: http://prometheus:9090
+    isDefault: true
+    editable: true
diff --git a/hw3/pics/business_dashboard.jpg b/hw3/pics/business_dashboard.jpg
new file mode 100644
index 00000000..0abdb880
Binary files /dev/null and b/hw3/pics/business_dashboard.jpg differ
diff --git a/hw3/pics/tech_dashboard.jpg b/hw3/pics/tech_dashboard.jpg
new file mode 100644
index 00000000..937ebdf0
Binary files /dev/null and b/hw3/pics/tech_dashboard.jpg differ
diff --git a/hw3/prometheus/prometheus.yml b/hw3/prometheus/prometheus.yml
new file mode 100644
index 00000000..046265e3
--- /dev/null
+++ b/hw3/prometheus/prometheus.yml
@@ -0,0 +1,8 @@
+global:
+  scrape_interval: 5s
+
+scrape_configs:
+  - job_name: 'shop_api'
+    static_configs:
+      - targets: ['app:8000']
+    metrics_path: /metrics
diff --git a/hw3/requirements.txt b/hw3/requirements.txt
new file mode 100644
index 00000000..415c999e
--- /dev/null
+++ b/hw3/requirements.txt
@@ -0,0 +1,4 @@
+fastapi
+uvicorn[standard]
+prometheus-fastapi-instrumentator
+pydantic
\ No newline at end of file
diff --git a/hw3/shop_api/__init__.py b/hw3/shop_api/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw3/shop_api/main.py b/hw3/shop_api/main.py
new file mode 100644
index 00000000..030e07d8
--- /dev/null
+++ b/hw3/shop_api/main.py
@@ -0,0 +1,11 @@
+from fastapi import FastAPI
+from shop_api.routers import items, carts, chat
+from prometheus_fastapi_instrumentator import Instrumentator
+
+
+app = FastAPI(title="Shop API")
+Instrumentator().instrument(app).expose(app)
+
+app.include_router(items.router)
+app.include_router(carts.router)
+app.include_router(chat.router)
\ No newline at end of file
diff --git a/hw3/shop_api/metrics.py b/hw3/shop_api/metrics.py
new file mode 100644
index 00000000..0b18aff2
--- /dev/null
+++ b/hw3/shop_api/metrics.py
@@ -0,0 +1,8 @@
+from prometheus_client import Counter, Gauge
+
+carts_created_counter = Counter(
+    "shop_carts_created_total", "Total number of carts created"
+)
+items_in_stock_gauge = Gauge(
+    "shop_items_total", "Current number of non-deleted items in stock"
+)
diff --git a/hw3/shop_api/models/__init__.py b/hw3/shop_api/models/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw3/shop_api/routers/__init__.py b/hw3/shop_api/routers/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw3/shop_api/routers/carts.py b/hw3/shop_api/routers/carts.py
new file mode 100644
index 00000000..37076862
--- /dev/null
+++ b/hw3/shop_api/routers/carts.py
@@ -0,0 +1,60 @@
+from fastapi import APIRouter, HTTPException, Query, Path, Response
+from shop_api.schemas.cart import Cart
+from shop_api.utils.cart_utils import compute_cart
+from shop_api.metrics import carts_created_counter
+from shop_api.storage.memory import _carts, _items, _lock, _next_cart_id
+from typing import Optional, List
+
+
+router = APIRouter(prefix="/cart", tags=["carts"])
+
+@router.post("/", status_code=201)
+def create_cart(response: Response):
+    global _next_cart_id
+    with _lock:
+        cid = _next_cart_id
+        _next_cart_id += 1
+        _carts[cid] = {}
+    response.headers["Location"] = f"/cart/{cid}"
+    carts_created_counter.inc()
+    return {"id": cid}
+
+@router.get("/{id}", response_model=Cart)
+def get_cart(id: int = Path(..., gt=0)):
+    try:
+        return compute_cart(id)
+    except KeyError:
+        raise HTTPException(status_code=404, detail="cart not found")
+
+@router.get("/", response_model=List[Cart])
+def list_carts(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    min_quantity: Optional[int] = Query(None, ge=0),
+    max_quantity: Optional[int] = Query(None, ge=0),
+):
+    carts = []
+    for cid in sorted(_carts.keys()):
+        cart = compute_cart(cid)
+        total_qty = sum(i.quantity for i in cart.items)
+        if min_quantity is not None and total_qty < min_quantity:
+            continue
+        if max_quantity is not None and total_qty > max_quantity:
+            continue
+        if min_price is not None and cart.price < min_price:
+            continue
+        if max_price is not None and cart.price > max_price:
+            continue
+        carts.append(cart)
+    return carts[offset: offset + limit]
+
+@router.post("/{cart_id}/add/{item_id}", response_model=Cart)
+def add_item(cart_id: int, item_id: int):
+    if cart_id not in _carts:
+        raise HTTPException(status_code=404, detail="cart not found")
+    if item_id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    _carts[cart_id][item_id] = _carts[cart_id].get(item_id, 0) + 1
+    return compute_cart(cart_id)
diff --git a/hw3/shop_api/routers/chat.py b/hw3/shop_api/routers/chat.py
new file mode 100644
index 00000000..ef026015
--- /dev/null
+++ b/hw3/shop_api/routers/chat.py
@@ -0,0 +1,39 @@
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+from collections import defaultdict
+import random
+import string
+from typing import Dict, List
+from prometheus_client import Counter, Gauge
+
+ws_connections = Gauge("shop_ws_connections", "Active WebSocket connections", ["chat_name"])
+ws_messages_total = Counter("shop_ws_messages_total", "Total WebSocket messages sent", ["chat_name"])
+
+router = APIRouter(prefix="/chat", tags=["chat"])
+
+chat_rooms: Dict[str, List[WebSocket]] = defaultdict(list)
+usernames: Dict[WebSocket, str] = {}
+
+def random_username() -> str:
+    return ''.join(random.choices(string.ascii_letters + string.digits, k=8))
+
+@router.websocket("/{chat_name}")
+async def websocket_chat(websocket: WebSocket, chat_name: str):
+    await websocket.accept()
+    username = random_username()
+    usernames[websocket] = username
+    chat_rooms[chat_name].append(websocket)
+    ws_connections.labels(chat_name=chat_name).inc()  # <--- увеличиваем число соединений
+
+    try:
+        while True:
+            data = await websocket.receive_text()
+            message = f"{username} :: {data}"
+            for ws in chat_rooms[chat_name]:
+                if ws != websocket:
+                    await ws.send_text(message)
+                    ws_messages_total.labels(chat_name=chat_name).inc()  # <--- увеличиваем счетчик сообщений
+    except WebSocketDisconnect:
+        chat_rooms[chat_name].remove(websocket)
+        del usernames[websocket]
+        ws_connections.labels(chat_name=chat_name).dec()  # <--- уменьшаем число соединений
+
diff --git a/hw3/shop_api/routers/items.py b/hw3/shop_api/routers/items.py
new file mode 100644
index 00000000..e432edb8
--- /dev/null
+++ b/hw3/shop_api/routers/items.py
@@ -0,0 +1,83 @@
+from fastapi import APIRouter, HTTPException, Query, Response
+from shop_api.schemas.item import Item, ItemCreate
+from shop_api.storage.memory import _items, _lock, _next_item_id
+from typing import Optional, List
+from shop_api.metrics import items_in_stock_gauge
+
+router = APIRouter(prefix="/item", tags=["items"])
+
+@router.post("/", response_model=Item, status_code=201)
+def create_item(item: ItemCreate):
+    global _next_item_id
+    with _lock:
+        iid = _next_item_id
+        _next_item_id += 1
+        new_item = Item(id=iid, name=item.name, price=item.price)
+        _items[iid] = new_item
+        items_in_stock_gauge.inc()
+    return new_item
+
+@router.get("/{id}", response_model=Item)
+def get_item(id: int):
+    item = _items.get(id)
+    if not item or item.deleted:
+        raise HTTPException(status_code=404, detail="item not found")
+    return item
+
+@router.get("/", response_model=List[Item])
+def list_items(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    show_deleted: bool = Query(False),
+):
+    items = []
+    for it in _items.values():
+        if not show_deleted and it.deleted:
+            continue
+        if min_price is not None and it.price < min_price:
+            continue
+        if max_price is not None and it.price > max_price:
+            continue
+        items.append(it)
+    return items[offset: offset + limit]
+
+@router.put("/{id}", response_model=Item)
+def replace_item(id: int, item: ItemCreate):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    existing = _items[id]
+    existing.name = item.name
+    existing.price = item.price
+    _items[id] = existing
+    return existing
+
+@router.patch("/{id}", response_model=Item)
+def patch_item(id: int, patch: dict):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    item = _items[id]
+    if item.deleted:
+        return Response(status_code=304)
+    allowed_keys = {"name", "price"}
+    if not set(patch.keys()).issubset(allowed_keys):
+        raise HTTPException(status_code=422)
+    if "price" in patch:
+        price = patch["price"]
+        if price is not None and price < 0:
+            raise HTTPException(status_code=422)
+        item.price = price
+    if "name" in patch:
+        item.name = patch["name"]
+    _items[id] = item
+    return item
+
+@router.delete("/{id}")
+def delete_item(id: int):
+    item = _items.get(id)
+    if not item:
+        raise HTTPException(status_code=404, detail="Item not found")
+    if not item.deleted:
+        item.deleted = True
+        items_in_stock_gauge.dec()
\ No newline at end of file
diff --git a/hw3/shop_api/schemas/__init__.py b/hw3/shop_api/schemas/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw3/shop_api/schemas/cart.py b/hw3/shop_api/schemas/cart.py
new file mode 100644
index 00000000..4e3ed90c
--- /dev/null
+++ b/hw3/shop_api/schemas/cart.py
@@ -0,0 +1,14 @@
+from pydantic import BaseModel
+from typing import List
+
+
+class CartItem(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+class Cart(BaseModel):
+    id: int
+    items: List[CartItem]
+    price: float
\ No newline at end of file
diff --git a/hw3/shop_api/schemas/item.py b/hw3/shop_api/schemas/item.py
new file mode 100644
index 00000000..53021cde
--- /dev/null
+++ b/hw3/shop_api/schemas/item.py
@@ -0,0 +1,18 @@
+from pydantic import BaseModel, Field
+from typing import Optional
+
+
+class ItemBase(BaseModel):
+    name: str
+    price: float = Field(..., ge=0)
+
+class ItemCreate(ItemBase):
+    pass
+
+class Item(ItemBase):
+    id: int
+    deleted: bool = False
+
+class ItemPatch(BaseModel):
+    name: Optional[str]
+    price: Optional[float]
\ No newline at end of file
diff --git a/hw3/shop_api/storage/__init__.py b/hw3/shop_api/storage/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw3/shop_api/storage/memory.py b/hw3/shop_api/storage/memory.py
new file mode 100644
index 00000000..e769f81d
--- /dev/null
+++ b/hw3/shop_api/storage/memory.py
@@ -0,0 +1,9 @@
+from typing import Dict
+from threading import Lock
+from shop_api.schemas.item import Item
+
+_items: Dict[int, Item] = {}
+_carts: Dict[int, Dict[int, int]] = {}
+_next_item_id = 1
+_next_cart_id = 1
+_lock = Lock()
diff --git a/hw3/shop_api/utils/cart_utils.py b/hw3/shop_api/utils/cart_utils.py
new file mode 100644
index 00000000..b0c65c2e
--- /dev/null
+++ b/hw3/shop_api/utils/cart_utils.py
@@ -0,0 +1,20 @@
+from shop_api.schemas.cart import Cart, CartItem
+from shop_api.storage.memory import _carts, _items
+
+
+def compute_cart(cart_id: int) -> Cart:
+    if cart_id not in _carts:
+        raise KeyError
+    bag = _carts[cart_id]
+    items_out = []
+    total = 0.0
+    for iid, qty in bag.items():
+        item = _items.get(iid)
+        if item is None:
+            name, available = "", False
+        else:
+            name, available = item.name, not item.deleted
+        items_out.append(CartItem(id=iid, name=name, quantity=qty, available=available))
+        if item and not item.deleted:
+            total += item.price * qty
+    return Cart(id=cart_id, items=items_out, price=total)
\ No newline at end of file
diff --git a/hw3/test.py b/hw3/test.py
new file mode 100644
index 00000000..a05b0cca
--- /dev/null
+++ b/hw3/test.py
@@ -0,0 +1,102 @@
+import asyncio
+import random
+import string
+import threading
+import time
+import requests
+import websockets
+from http import HTTPStatus
+
+API_URL = "http://localhost:8000"
+WS_URL = "ws://localhost:8000/chat"
+
+def random_name(length=8):
+    return ''.join(random.choices(string.ascii_lowercase, k=length))
+
+def random_price():
+    return round(random.uniform(5, 500), 2)
+
+
+def simulate_http_load():
+    while True:
+        try:
+            item = {"name": f"Item {random_name()}", "price": random_price()}
+            start = time.perf_counter()
+            r = requests.post(f"{API_URL}/item", json=item)
+            latency = time.perf_counter() - start
+
+            if r.status_code == HTTPStatus.CREATED:
+                item_id = r.json()["id"]
+                requests.get(f"{API_URL}/item/{item_id}")
+                requests.put(
+                    f"{API_URL}/item/{item_id}",
+                    json={"name": item["name"], "price": item["price"] + 1},
+                )
+                if random.random() < 0.2:
+                    requests.delete(f"{API_URL}/item/{item_id}")
+            else:
+                requests.get(f"{API_URL}/item/99999999")
+
+            cart_response = requests.post(f"{API_URL}/cart")
+            if cart_response.status_code == HTTPStatus.CREATED:
+                cart_id = cart_response.json()["id"]
+                if r.status_code == HTTPStatus.CREATED:
+                    requests.post(f"{API_URL}/cart/{cart_id}/add/{r.json()['id']}")
+                requests.get(f"{API_URL}/cart/{cart_id}")
+            else:
+                requests.get(f"{API_URL}/cart/-1")
+
+            requests.get(f"{API_URL}/item", params={
+                "min_price": random.uniform(1, 50),
+                "max_price": random.uniform(100, 500),
+                "offset": random.randint(0, 5),
+                "limit": random.randint(1, 10),
+            })
+
+            requests.get(f"{API_URL}/cart", params={
+                "min_price": random.uniform(1, 50),
+                "max_price": random.uniform(100, 500),
+                "offset": random.randint(0, 5),
+                "limit": random.randint(1, 10),
+            })
+
+            asyncio.run(asyncio.sleep(random.uniform(0.05, 0.2)))
+
+        except Exception as e:
+            print(f"[HTTP Error] {e}")
+
+
+async def simulate_websocket_load(chat_name: str):
+    uri = f"{WS_URL}/{chat_name}"
+    try:
+        async with websockets.connect(uri) as ws:
+            for _ in range(random.randint(5, 15)):
+                msg = f"Hello from {random_name()}!"
+                await ws.send(msg)
+                try:
+                    await asyncio.wait_for(ws.recv(), timeout=1)
+                except asyncio.TimeoutError:
+                    pass
+                await asyncio.sleep(random.uniform(0.2, 1.0))
+    except Exception as e:
+        print(f"[WS Error] {e}")
+
+
+def run_websocket_load():
+    asyncio.run(simulate_websocket_load(random.choice(["general", "orders", "support", "promo"])))
+
+
+if __name__ == "__main__":
+    print("Started")
+
+    for _ in range(8):
+        threading.Thread(target=simulate_http_load, daemon=True).start()
+
+    for _ in range(4):
+        threading.Thread(target=run_websocket_load, daemon=True).start()
+
+    try:
+        while True:
+            time.sleep(2)
+    except KeyboardInterrupt:
+        print("Stopped")
diff --git a/hw4/Dockerfile b/hw4/Dockerfile
new file mode 100644
index 00000000..f08e675f
--- /dev/null
+++ b/hw4/Dockerfile
@@ -0,0 +1,13 @@
+FROM python:3.11-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+EXPOSE 8000
+
+CMD ["uvicorn", "shop_api.main:app", "--host", "0.0.0.0", "--port", "8000"]
diff --git a/hw4/README.md b/hw4/README.md
new file mode 100644
index 00000000..cad0c96f
--- /dev/null
+++ b/hw4/README.md
@@ -0,0 +1,9 @@
+### Технический мониторинг
+![Tech Dashboard](./pics/tech_dashboard.jpg)
+
+### Бизнес-метрики
+![Business Dashboard](./pics/business_dashboard.jpg)
+
+### Запуск:
+```bash
+docker-compose up --build
\ No newline at end of file
diff --git a/hw4/__init__.py b/hw4/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/docker-compose.yml b/hw4/docker-compose.yml
new file mode 100644
index 00000000..01a84a56
--- /dev/null
+++ b/hw4/docker-compose.yml
@@ -0,0 +1,51 @@
+services:
+  db:
+    image: postgres:15
+    environment:
+      POSTGRES_USER: shop_user
+      POSTGRES_PASSWORD: shop_pass
+      POSTGRES_DB: shop_db
+    ports:
+      - "5432:5432"
+    volumes:
+      - db_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U shop_user -d shop_db"]
+      interval: 2s
+      timeout: 2s
+      retries: 10
+
+  shop-api:
+    build: .
+    depends_on:
+      db:
+        condition: service_healthy
+    environment:
+      DATABASE_URL: postgresql+asyncpg://shop_user:shop_pass@db:5432/shop_db
+    ports:
+      - "8000:8000"
+
+  prometheus:
+    image: prom/prometheus:latest
+    volumes:
+      - ./prometheus:/etc/prometheus
+    command:
+      - "--config.file=/etc/prometheus/prometheus.yml"
+    ports:
+      - "9090:9090"
+
+  grafana:
+    image: grafana/grafana:latest
+    environment:
+      - GF_SECURITY_ADMIN_PASSWORD=admin
+    ports:
+      - "3000:3000"
+    depends_on:
+      - prometheus
+    volumes:
+      - grafana_data:/var/lib/grafana
+      - ./grafana/provisioning:/etc/grafana/provisioning
+
+volumes:
+  db_data:
+  grafana_data:
diff --git a/hw4/grafana/provisioning/dashboards/dashboard.yml b/hw4/grafana/provisioning/dashboards/dashboard.yml
new file mode 100644
index 00000000..472a2279
--- /dev/null
+++ b/hw4/grafana/provisioning/dashboards/dashboard.yml
@@ -0,0 +1,11 @@
+apiVersion: 1
+
+providers:
+  - name: "Shop API Technical"
+    folder: "Tech"
+    options:
+      path: /etc/grafana/provisioning/dashboards
+  - name: "Shop API Business"
+    folder: "Business"
+    options:
+      path: /etc/grafana/provisioning/dashboards
diff --git a/hw4/grafana/provisioning/dashboards/shop_api_business_dashboard.json b/hw4/grafana/provisioning/dashboards/shop_api_business_dashboard.json
new file mode 100644
index 00000000..794d4643
--- /dev/null
+++ b/hw4/grafana/provisioning/dashboards/shop_api_business_dashboard.json
@@ -0,0 +1,334 @@
+{
+  "annotations": {
+    "list": [
+      {
+        "builtIn": 1,
+        "datasource": {
+          "type": "grafana",
+          "uid": "-- Grafana --"
+        },
+        "enable": true,
+        "hide": true,
+        "iconColor": "rgba(0, 211, 255, 1)",
+        "name": "Annotations & Alerts",
+        "type": "dashboard"
+      }
+    ]
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": 4,
+  "links": [],
+  "panels": [
+    {
+      "datasource": {
+        "type": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 15,
+        "x": 0,
+        "y": 0
+      },
+      "id": 3,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "editorMode": "code",
+          "expr": "rate(shop_carts_created_total[1m])",
+          "legendFormat": "Carts per minute",
+          "range": true,
+          "refId": "A"
+        }
+      ],
+      "title": "Carts Created per Minute",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 8,
+        "x": 15,
+        "y": 0
+      },
+      "id": 2,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "percentChangeColorMode": "standard",
+        "reduceOptions": {
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": "",
+          "values": false
+        },
+        "showPercentChange": false,
+        "textMode": "auto",
+        "wideLayout": true
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "count(shop_ws_connections)",
+          "refId": "A"
+        }
+      ],
+      "title": "Active Chat Rooms",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 15,
+        "x": 0,
+        "y": 6
+      },
+      "id": 4,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "sum(rate(shop_ws_messages_total[1m])) by (chat_name)",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Chat Messages per Minute",
+      "type": "timeseries"
+    },
+    {
+      "fieldConfig": {
+        "defaults": {
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 8,
+        "x": 15,
+        "y": 6
+      },
+      "id": 1,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "percentChangeColorMode": "standard",
+        "reduceOptions": {
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": "",
+          "values": false
+        },
+        "showPercentChange": false,
+        "textMode": "auto",
+        "wideLayout": true
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "sum(shop_items_total)",
+          "refId": "A"
+        }
+      ],
+      "title": "Total Items in Stock",
+      "type": "stat"
+    }
+  ],
+  "preload": false,
+  "refresh": "",
+  "schemaVersion": 42,
+  "tags": [],
+  "templating": {
+    "list": []
+  },
+  "timepicker": {},
+  "timezone": "browser",
+  "title": "Business Metrics",
+  "uid": "440d983f-0b3d-4579-b85d-3ee2dad1babd",
+  "version": 2
+}
\ No newline at end of file
diff --git a/hw4/grafana/provisioning/dashboards/shop_api_dashboard.json b/hw4/grafana/provisioning/dashboards/shop_api_dashboard.json
new file mode 100644
index 00000000..5779d8e0
--- /dev/null
+++ b/hw4/grafana/provisioning/dashboards/shop_api_dashboard.json
@@ -0,0 +1,408 @@
+{
+  "annotations": {
+    "list": [
+      {
+        "builtIn": 1,
+        "datasource": {
+          "type": "grafana",
+          "uid": "-- Grafana --"
+        },
+        "enable": true,
+        "hide": true,
+        "iconColor": "rgba(0, 211, 255, 1)",
+        "name": "Annotations & Alerts",
+        "type": "dashboard"
+      }
+    ]
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": 1,
+  "links": [],
+  "panels": [
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 0,
+        "y": 0
+      },
+      "id": 1,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "editorMode": "code",
+          "exemplar": false,
+          "expr": "sum(rate(http_requests_total[1m])) by (method, handler)",
+          "legendFormat": "{{method}} {{handler}}",
+          "range": true,
+          "refId": "A"
+        }
+      ],
+      "title": "HTTP Requests per Second",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 12,
+        "y": 0
+      },
+      "id": 2,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket[5m])) by (le))",
+          "legendFormat": "p95",
+          "refId": "A"
+        }
+      ],
+      "title": "Request Duration (p95)",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 12,
+        "x": 0,
+        "y": 7
+      },
+      "id": 3,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "shop_ws_connections",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Active WebSocket Connections",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus_ds"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "barWidthFactor": 0.6,
+            "drawStyle": "line",
+            "fillOpacity": 0,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "showValues": false,
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": 0
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 6,
+        "w": 12,
+        "x": 12,
+        "y": 7
+      },
+      "id": 4,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "hideZeros": false,
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "pluginVersion": "12.2.0",
+      "targets": [
+        {
+          "expr": "increase(shop_ws_messages_total[5m])",
+          "legendFormat": "{{chat_name}}",
+          "refId": "A"
+        }
+      ],
+      "title": "WebSocket Messages Sent",
+      "type": "timeseries"
+    }
+  ],
+  "preload": false,
+  "refresh": "",
+  "schemaVersion": 42,
+  "tags": [],
+  "templating": {
+    "list": []
+  },
+  "timepicker": {},
+  "timezone": "browser",
+  "title": "Shop API Dashboard",
+  "uid": "ecd408fb-c57c-4ba2-8452-260e76f954ed",
+  "version": 3
+}
\ No newline at end of file
diff --git a/hw4/grafana/provisioning/datasources/datasource.yml b/hw4/grafana/provisioning/datasources/datasource.yml
new file mode 100644
index 00000000..7285dbe4
--- /dev/null
+++ b/hw4/grafana/provisioning/datasources/datasource.yml
@@ -0,0 +1,11 @@
+apiVersion: 1
+
+datasources:
+  - name: Prometheus
+    type: prometheus
+    access: proxy
+    orgId: 1
+    uid: prometheus_ds
+    url: http://prometheus:9090
+    isDefault: true
+    editable: true
diff --git a/hw4/pics/business_dashboard.jpg b/hw4/pics/business_dashboard.jpg
new file mode 100644
index 00000000..0abdb880
Binary files /dev/null and b/hw4/pics/business_dashboard.jpg differ
diff --git a/hw4/pics/tech_dashboard.jpg b/hw4/pics/tech_dashboard.jpg
new file mode 100644
index 00000000..937ebdf0
Binary files /dev/null and b/hw4/pics/tech_dashboard.jpg differ
diff --git a/hw4/prometheus/prometheus.yml b/hw4/prometheus/prometheus.yml
new file mode 100644
index 00000000..046265e3
--- /dev/null
+++ b/hw4/prometheus/prometheus.yml
@@ -0,0 +1,8 @@
+global:
+  scrape_interval: 5s
+
+scrape_configs:
+  - job_name: 'shop_api'
+    static_configs:
+      - targets: ['app:8000']
+    metrics_path: /metrics
diff --git a/hw4/requirements.txt b/hw4/requirements.txt
new file mode 100644
index 00000000..76867af0
--- /dev/null
+++ b/hw4/requirements.txt
@@ -0,0 +1,6 @@
+fastapi
+uvicorn[standard]
+prometheus-fastapi-instrumentator
+pydantic
+sqlalchemy
+asyncpg
\ No newline at end of file
diff --git a/hw4/shop_api/__init__.py b/hw4/shop_api/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/shop_api/database.py b/hw4/shop_api/database.py
new file mode 100644
index 00000000..3319d7b3
--- /dev/null
+++ b/hw4/shop_api/database.py
@@ -0,0 +1,17 @@
+import os
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
+from sqlalchemy.orm import sessionmaker, declarative_base
+
+DATABASE_URL = os.getenv(
+    "DATABASE_URL",
+    "postgresql+asyncpg://shop_user:shop_pass@db:5432/shop_db"
+)
+
+engine = create_async_engine(DATABASE_URL, echo=True, future=True)
+async_session_maker = sessionmaker(engine, expire_on_commit=False, class_=AsyncSession)
+Base = declarative_base()
+
+
+async def get_session() -> AsyncSession:
+    async with async_session_maker() as session:
+        yield session
diff --git a/hw4/shop_api/main.py b/hw4/shop_api/main.py
new file mode 100644
index 00000000..1d866fb9
--- /dev/null
+++ b/hw4/shop_api/main.py
@@ -0,0 +1,13 @@
+from fastapi import FastAPI
+from shop_api.routers import items, carts
+from shop_api.database import Base, engine
+
+app = FastAPI(title="Shop API")
+
+@app.on_event("startup")
+async def on_startup():
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+app.include_router(items.router)
+app.include_router(carts.router)
diff --git a/hw4/shop_api/metrics.py b/hw4/shop_api/metrics.py
new file mode 100644
index 00000000..0b18aff2
--- /dev/null
+++ b/hw4/shop_api/metrics.py
@@ -0,0 +1,8 @@
+from prometheus_client import Counter, Gauge
+
+carts_created_counter = Counter(
+    "shop_carts_created_total", "Total number of carts created"
+)
+items_in_stock_gauge = Gauge(
+    "shop_items_total", "Current number of non-deleted items in stock"
+)
diff --git a/hw4/shop_api/models/__init__.py b/hw4/shop_api/models/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/shop_api/models/cart.py b/hw4/shop_api/models/cart.py
new file mode 100644
index 00000000..2695bee4
--- /dev/null
+++ b/hw4/shop_api/models/cart.py
@@ -0,0 +1,22 @@
+from sqlalchemy import Column, Integer, Float, ForeignKey
+from sqlalchemy.orm import relationship
+from shop_api.database import Base
+
+
+class Cart(Base):
+    __tablename__ = "carts"
+
+    id = Column(Integer, primary_key=True, index=True)
+    price = Column(Float, default=0.0)
+    items = relationship("CartItem", back_populates="cart", cascade="all, delete-orphan")
+
+
+class CartItem(Base):
+    __tablename__ = "cart_items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    cart_id = Column(Integer, ForeignKey("carts.id"))
+    item_id = Column(Integer, ForeignKey("items.id"))
+    quantity = Column(Integer, default=1)
+
+    cart = relationship("Cart", back_populates="items")
\ No newline at end of file
diff --git a/hw4/shop_api/models/item.py b/hw4/shop_api/models/item.py
new file mode 100644
index 00000000..184b6617
--- /dev/null
+++ b/hw4/shop_api/models/item.py
@@ -0,0 +1,10 @@
+from sqlalchemy import Column, Integer, String, Float, Boolean
+from shop_api.database import Base
+
+class Item(Base):
+    __tablename__ = "items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String, nullable=False)
+    price = Column(Float, nullable=False)
+    deleted = Column(Boolean, default=False)
\ No newline at end of file
diff --git a/hw4/shop_api/routers/__init__.py b/hw4/shop_api/routers/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/shop_api/routers/carts.py b/hw4/shop_api/routers/carts.py
new file mode 100644
index 00000000..38b0444f
--- /dev/null
+++ b/hw4/shop_api/routers/carts.py
@@ -0,0 +1,80 @@
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func
+from typing import List, Optional
+
+from shop_api.database import get_session
+from shop_api.models.cart import Cart, CartItem
+from shop_api.models.item import Item
+from shop_api.schemas.cart import CartOut, CartItemOut
+from shop_api.metrics import carts_created_counter
+
+router = APIRouter(prefix="/cart", tags=["cart"])
+
+
+@router.post("/", status_code=201)
+async def create_cart(session: AsyncSession = Depends(get_session)):
+    cart = Cart()
+    session.add(cart)
+    await session.commit()
+    await session.refresh(cart)
+
+    carts_created_counter.inc()
+    return {"id": cart.id}
+
+
+@router.post("/{cart_id}/add/{item_id}", status_code=200)
+async def add_item_to_cart(cart_id: int, item_id: int, session: AsyncSession = Depends(get_session)):
+    cart = await session.get(Cart, cart_id)
+    if not cart:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    item = await session.get(Item, item_id)
+    if not item or item.deleted:
+        raise HTTPException(status_code=404, detail="Item not found")
+
+    result = await session.execute(
+        select(CartItem).where(CartItem.cart_id == cart_id, CartItem.item_id == item_id)
+    )
+    cart_item = result.scalar_one_or_none()
+
+    if cart_item:
+        cart_item.quantity += 1
+    else:
+        cart_item = CartItem(cart_id=cart_id, item_id=item_id, quantity=1)
+        session.add(cart_item)
+
+    await session.commit()
+    return {"status": "ok"}
+
+
+@router.get("/{cart_id}", response_model=CartOut)
+async def get_cart(cart_id: int, session: AsyncSession = Depends(get_session)):
+    cart = await session.get(Cart, cart_id)
+    if not cart:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    result = await session.execute(
+        select(CartItem, Item)
+        .join(Item, CartItem.item_id == Item.id)
+        .where(CartItem.cart_id == cart_id)
+    )
+
+    cart_items = []
+    total_price = 0.0
+    for cart_item, item in result.all():
+        cart_items.append(
+            CartItemOut(
+                id=item.id,
+                name=item.name,
+                quantity=cart_item.quantity,
+                available=not item.deleted,
+            )
+        )
+        if not item.deleted:
+            total_price += item.price * cart_item.quantity
+
+    cart.price = total_price
+    await session.commit()
+
+    return CartOut(id=cart.id, items=cart_items, price=total_price)
diff --git a/hw4/shop_api/routers/chat.py b/hw4/shop_api/routers/chat.py
new file mode 100644
index 00000000..ef026015
--- /dev/null
+++ b/hw4/shop_api/routers/chat.py
@@ -0,0 +1,39 @@
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+from collections import defaultdict
+import random
+import string
+from typing import Dict, List
+from prometheus_client import Counter, Gauge
+
+ws_connections = Gauge("shop_ws_connections", "Active WebSocket connections", ["chat_name"])
+ws_messages_total = Counter("shop_ws_messages_total", "Total WebSocket messages sent", ["chat_name"])
+
+router = APIRouter(prefix="/chat", tags=["chat"])
+
+chat_rooms: Dict[str, List[WebSocket]] = defaultdict(list)
+usernames: Dict[WebSocket, str] = {}
+
+def random_username() -> str:
+    return ''.join(random.choices(string.ascii_letters + string.digits, k=8))
+
+@router.websocket("/{chat_name}")
+async def websocket_chat(websocket: WebSocket, chat_name: str):
+    await websocket.accept()
+    username = random_username()
+    usernames[websocket] = username
+    chat_rooms[chat_name].append(websocket)
+    ws_connections.labels(chat_name=chat_name).inc()  # <--- увеличиваем число соединений
+
+    try:
+        while True:
+            data = await websocket.receive_text()
+            message = f"{username} :: {data}"
+            for ws in chat_rooms[chat_name]:
+                if ws != websocket:
+                    await ws.send_text(message)
+                    ws_messages_total.labels(chat_name=chat_name).inc()  # <--- увеличиваем счетчик сообщений
+    except WebSocketDisconnect:
+        chat_rooms[chat_name].remove(websocket)
+        del usernames[websocket]
+        ws_connections.labels(chat_name=chat_name).dec()  # <--- уменьшаем число соединений
+
diff --git a/hw4/shop_api/routers/items.py b/hw4/shop_api/routers/items.py
new file mode 100644
index 00000000..2c3def81
--- /dev/null
+++ b/hw4/shop_api/routers/items.py
@@ -0,0 +1,63 @@
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+from typing import List, Optional
+
+from shop_api.database import get_session
+from shop_api.models.item import Item
+from shop_api.schemas.item import ItemCreate, ItemOut
+from shop_api.metrics import items_in_stock_gauge
+
+router = APIRouter(prefix="/item", tags=["item"])
+
+
+@router.post("/", response_model=ItemOut, status_code=201)
+async def create_item(item: ItemCreate, session: AsyncSession = Depends(get_session)):
+    new_item = Item(**item.dict())
+    session.add(new_item)
+    await session.commit()
+    await session.refresh(new_item)
+
+    items_in_stock_gauge.inc()
+    return new_item
+
+
+@router.get("/{item_id}", response_model=ItemOut)
+async def get_item(item_id: int, session: AsyncSession = Depends(get_session)):
+    item = await session.get(Item, item_id)
+    if not item or item.deleted:
+        raise HTTPException(status_code=404, detail="Item not found")
+    return item
+
+
+@router.get("/", response_model=List[ItemOut])
+async def list_items(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    show_deleted: bool = Query(False),
+    session: AsyncSession = Depends(get_session),
+):
+    query = select(Item)
+    if not show_deleted:
+        query = query.where(Item.deleted.is_(False))
+    if min_price is not None:
+        query = query.where(Item.price >= min_price)
+    if max_price is not None:
+        query = query.where(Item.price <= max_price)
+
+    result = await session.execute(query.offset(offset).limit(limit))
+    return result.scalars().all()
+
+
+@router.delete("/{item_id}", status_code=200)
+async def delete_item(item_id: int, session: AsyncSession = Depends(get_session)):
+    item = await session.get(Item, item_id)
+    if not item:
+        raise HTTPException(status_code=404, detail="Item not found")
+    if not item.deleted:
+        item.deleted = True
+        await session.commit()
+        items_in_stock_gauge.dec()
+    return {"status": "ok"}
diff --git a/hw4/shop_api/schemas/__init__.py b/hw4/shop_api/schemas/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/shop_api/schemas/cart.py b/hw4/shop_api/schemas/cart.py
new file mode 100644
index 00000000..c1ae093f
--- /dev/null
+++ b/hw4/shop_api/schemas/cart.py
@@ -0,0 +1,16 @@
+from pydantic import BaseModel
+from typing import List
+
+class CartItemOut(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+class CartOut(BaseModel):
+    id: int
+    items: List[CartItemOut]
+    price: float
+
+    class Config:
+        orm_mode = True
diff --git a/hw4/shop_api/schemas/item.py b/hw4/shop_api/schemas/item.py
new file mode 100644
index 00000000..9093763d
--- /dev/null
+++ b/hw4/shop_api/schemas/item.py
@@ -0,0 +1,18 @@
+from pydantic import BaseModel
+
+class ItemBase(BaseModel):
+    name: str
+    price: float
+
+class ItemCreate(ItemBase):
+    pass
+
+class ItemUpdate(ItemBase):
+    deleted: bool = False
+
+class ItemOut(ItemBase):
+    id: int
+    deleted: bool
+
+    class Config:
+        orm_mode = True
diff --git a/hw4/shop_api/storage/__init__.py b/hw4/shop_api/storage/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw4/shop_api/storage/memory.py b/hw4/shop_api/storage/memory.py
new file mode 100644
index 00000000..e769f81d
--- /dev/null
+++ b/hw4/shop_api/storage/memory.py
@@ -0,0 +1,9 @@
+from typing import Dict
+from threading import Lock
+from shop_api.schemas.item import Item
+
+_items: Dict[int, Item] = {}
+_carts: Dict[int, Dict[int, int]] = {}
+_next_item_id = 1
+_next_cart_id = 1
+_lock = Lock()
diff --git a/hw4/shop_api/utils/cart_utils.py b/hw4/shop_api/utils/cart_utils.py
new file mode 100644
index 00000000..b0c65c2e
--- /dev/null
+++ b/hw4/shop_api/utils/cart_utils.py
@@ -0,0 +1,20 @@
+from shop_api.schemas.cart import Cart, CartItem
+from shop_api.storage.memory import _carts, _items
+
+
+def compute_cart(cart_id: int) -> Cart:
+    if cart_id not in _carts:
+        raise KeyError
+    bag = _carts[cart_id]
+    items_out = []
+    total = 0.0
+    for iid, qty in bag.items():
+        item = _items.get(iid)
+        if item is None:
+            name, available = "", False
+        else:
+            name, available = item.name, not item.deleted
+        items_out.append(CartItem(id=iid, name=name, quantity=qty, available=available))
+        if item and not item.deleted:
+            total += item.price * qty
+    return Cart(id=cart_id, items=items_out, price=total)
\ No newline at end of file
diff --git a/hw4/test.py b/hw4/test.py
new file mode 100644
index 00000000..a05b0cca
--- /dev/null
+++ b/hw4/test.py
@@ -0,0 +1,102 @@
+import asyncio
+import random
+import string
+import threading
+import time
+import requests
+import websockets
+from http import HTTPStatus
+
+API_URL = "http://localhost:8000"
+WS_URL = "ws://localhost:8000/chat"
+
+def random_name(length=8):
+    return ''.join(random.choices(string.ascii_lowercase, k=length))
+
+def random_price():
+    return round(random.uniform(5, 500), 2)
+
+
+def simulate_http_load():
+    while True:
+        try:
+            item = {"name": f"Item {random_name()}", "price": random_price()}
+            start = time.perf_counter()
+            r = requests.post(f"{API_URL}/item", json=item)
+            latency = time.perf_counter() - start
+
+            if r.status_code == HTTPStatus.CREATED:
+                item_id = r.json()["id"]
+                requests.get(f"{API_URL}/item/{item_id}")
+                requests.put(
+                    f"{API_URL}/item/{item_id}",
+                    json={"name": item["name"], "price": item["price"] + 1},
+                )
+                if random.random() < 0.2:
+                    requests.delete(f"{API_URL}/item/{item_id}")
+            else:
+                requests.get(f"{API_URL}/item/99999999")
+
+            cart_response = requests.post(f"{API_URL}/cart")
+            if cart_response.status_code == HTTPStatus.CREATED:
+                cart_id = cart_response.json()["id"]
+                if r.status_code == HTTPStatus.CREATED:
+                    requests.post(f"{API_URL}/cart/{cart_id}/add/{r.json()['id']}")
+                requests.get(f"{API_URL}/cart/{cart_id}")
+            else:
+                requests.get(f"{API_URL}/cart/-1")
+
+            requests.get(f"{API_URL}/item", params={
+                "min_price": random.uniform(1, 50),
+                "max_price": random.uniform(100, 500),
+                "offset": random.randint(0, 5),
+                "limit": random.randint(1, 10),
+            })
+
+            requests.get(f"{API_URL}/cart", params={
+                "min_price": random.uniform(1, 50),
+                "max_price": random.uniform(100, 500),
+                "offset": random.randint(0, 5),
+                "limit": random.randint(1, 10),
+            })
+
+            asyncio.run(asyncio.sleep(random.uniform(0.05, 0.2)))
+
+        except Exception as e:
+            print(f"[HTTP Error] {e}")
+
+
+async def simulate_websocket_load(chat_name: str):
+    uri = f"{WS_URL}/{chat_name}"
+    try:
+        async with websockets.connect(uri) as ws:
+            for _ in range(random.randint(5, 15)):
+                msg = f"Hello from {random_name()}!"
+                await ws.send(msg)
+                try:
+                    await asyncio.wait_for(ws.recv(), timeout=1)
+                except asyncio.TimeoutError:
+                    pass
+                await asyncio.sleep(random.uniform(0.2, 1.0))
+    except Exception as e:
+        print(f"[WS Error] {e}")
+
+
+def run_websocket_load():
+    asyncio.run(simulate_websocket_load(random.choice(["general", "orders", "support", "promo"])))
+
+
+if __name__ == "__main__":
+    print("Started")
+
+    for _ in range(8):
+        threading.Thread(target=simulate_http_load, daemon=True).start()
+
+    for _ in range(4):
+        threading.Thread(target=run_websocket_load, daemon=True).start()
+
+    try:
+        while True:
+            time.sleep(2)
+    except KeyboardInterrupt:
+        print("Stopped")
diff --git a/hw4/test_db.py b/hw4/test_db.py
new file mode 100644
index 00000000..9138df32
--- /dev/null
+++ b/hw4/test_db.py
@@ -0,0 +1,13 @@
+import asyncio
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy import text
+
+DATABASE_URL = "postgresql+asyncpg://shop_user:shop_pass@localhost:5432/shop_db"
+engine = create_async_engine(DATABASE_URL)
+
+async def test_db():
+    async with engine.begin() as conn:
+        result = await conn.execute(text("SELECT 1;"))
+        print(result.fetchall())
+
+asyncio.run(test_db())
diff --git a/hw4/tx_demos/README.md b/hw4/tx_demos/README.md
new file mode 100644
index 00000000..b761192c
--- /dev/null
+++ b/hw4/tx_demos/README.md
@@ -0,0 +1,44 @@
+# HW4
+
+## Запуск проекта
+
+```bash
+docker compose up -d
+```
+
+## Структура базы данных 
+
+Таблицы:
+
+- carts (хранит корзины пользователей): id, price
+- items (хранит товары): id, name, price, deleted
+- cart_items (связывает корзины и товары многие ко многим): id, cart_id, item_id. quantity
+
+## Демонстрации транзакционных аномалий (dirty read, non-repeatable read, phantom)
+
+### Dirty read
+
+```bash
+python tx_demos/demo_dirty_read.py
+```
+
+В PostgreSQL не возникает даже при READ UNCOMMITTED, так как этот уровень фактически работает как READ COMMITTED. \
+Невозможно прочитать неподтверждённые изменения другой транзакции.
+
+### Non-repeatable read
+
+```bash
+python tx_demos/non_repeatable_read.py
+```
+
+Возможно при READ COMMITTED, потому что между двумя чтениями другая транзакция может изменить данные и зафиксировать изменения. \
+Данные, считанные повторно, могут измениться.
+
+### Phantom read
+
+```bash
+python tx_demos/demo_phantom_read.py
+```
+
+Возможно при REPEATABLE READ, но предотвращается при SERIALIZABLE. \
+Между двумя одинаковыми запросами может появиться (или исчезнуть) новая строка, удовлетворяющая условию выборки.
\ No newline at end of file
diff --git a/hw4/tx_demos/__init__.py b/hw4/tx_demos/__init__.py
new file mode 100644
index 00000000..8538f779
--- /dev/null
+++ b/hw4/tx_demos/__init__.py
@@ -0,0 +1 @@
+# package marker for tx_demos
diff --git a/hw4/tx_demos/db_setup.py b/hw4/tx_demos/db_setup.py
new file mode 100644
index 00000000..19840159
--- /dev/null
+++ b/hw4/tx_demos/db_setup.py
@@ -0,0 +1,79 @@
+import asyncio
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import create_async_engine
+
+DATABASE_URL = "postgresql+asyncpg://shop_user:shop_pass@localhost:5432/shop_db"
+engine = create_async_engine(DATABASE_URL)
+
+
+async def create_tables():
+    async with engine.begin() as conn:
+        await conn.execute(
+            text(
+                """
+                CREATE TABLE IF NOT EXISTS carts (
+                    id SERIAL PRIMARY KEY,
+                    price FLOAT DEFAULT 0.0
+                );
+                """
+            )
+        )
+
+        await conn.execute(
+            text(
+                """
+                CREATE TABLE IF NOT EXISTS items (
+                    id SERIAL PRIMARY KEY,
+                    name TEXT NOT NULL,
+                    price FLOAT NOT NULL,
+                    deleted BOOLEAN DEFAULT FALSE
+                );
+                """
+            )
+        )
+
+        await conn.execute(
+            text(
+                """
+                CREATE TABLE IF NOT EXISTS cart_items (
+                    id SERIAL PRIMARY KEY,
+                    cart_id INTEGER REFERENCES carts(id) ON DELETE CASCADE,
+                    item_id INTEGER REFERENCES items(id),
+                    quantity INTEGER DEFAULT 1
+                );
+                """
+            )
+        )
+
+
+async def seed_default():
+    async with engine.begin() as conn:
+        await conn.execute(
+            text(
+                """
+                INSERT INTO carts (price) VALUES (100.0)
+                ON CONFLICT DO NOTHING;
+                """
+            )
+        )
+
+        await conn.execute(
+            text(
+                """
+                INSERT INTO items (name, price, deleted)
+                VALUES ('Item A', 10.0, FALSE),
+                       ('Item B', 20.0, FALSE)
+                ON CONFLICT DO NOTHING;
+                """
+            )
+        )
+
+
+async def prepare():
+    await create_tables()
+    await seed_default()
+
+
+if __name__ == "__main__":
+    asyncio.run(prepare())
+    print("Done.")
diff --git a/hw4/tx_demos/demo_dirty_read.py b/hw4/tx_demos/demo_dirty_read.py
new file mode 100644
index 00000000..0fd32410
--- /dev/null
+++ b/hw4/tx_demos/demo_dirty_read.py
@@ -0,0 +1,49 @@
+import asyncio
+from sqlalchemy import text
+from tx_demos.db_setup import prepare, engine
+
+
+async def dirty_read_demo(isolation_level: str):
+    async with engine.connect() as conn1:
+        trans1 = await conn1.begin()
+        try:
+            await conn1.execute(text(f"SET TRANSACTION ISOLATION LEVEL {isolation_level}"))
+            print(f"[T1] Установлен уровень изоляции: {isolation_level}. Обновляю carts.price -> 999 (без фиксации)")
+            await conn1.execute(text("UPDATE carts SET price = 999 WHERE id = 1"))
+
+            async with engine.connect() as conn2:
+                trans2 = await conn2.begin()
+                try:
+                    await conn2.execute(text(f"SET TRANSACTION ISOLATION LEVEL {isolation_level}"))
+                    print("[T2] Выполняю чтение значения price для корзины с id = 1")
+                    res = await conn2.execute(text("SELECT price FROM carts WHERE id = 1"))
+                    row = res.first()
+                    print(f"[T2] Получено значение price: {row[0] if row else 'нет данных'}")
+                    await trans2.commit()
+                    print("[T2] Транзакция зафиксирована")
+                except Exception as e:
+                    await trans2.rollback()
+                    print(f"[T2] Ошибка: {e}. Транзакция отменена")
+
+            print("[T1] Отменяю изменения, фиксации не будет")
+            await trans1.rollback()
+        except Exception as e:
+            print(f"[T1] Ошибка: {e}. Транзакция отменена")
+            await trans1.rollback()
+
+
+async def main():
+    print("Подготовка базы данных: создание таблиц и тестовых данных")
+    await prepare()
+
+    print("\n=== Демонстрация dirty read (READ UNCOMMITTED) ===")
+    await dirty_read_demo("READ UNCOMMITTED")
+
+    print("\n=== Демонстрация без dirty read (READ COMMITTED) ===")
+    await dirty_read_demo("READ COMMITTED")
+
+    print("\nЗавершено")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())
diff --git a/hw4/tx_demos/demo_non_repeatable_read.py b/hw4/tx_demos/demo_non_repeatable_read.py
new file mode 100644
index 00000000..9041497b
--- /dev/null
+++ b/hw4/tx_demos/demo_non_repeatable_read.py
@@ -0,0 +1,60 @@
+import asyncio
+from sqlalchemy import text
+from tx_demos.db_setup import prepare, engine
+
+
+async def non_repeatable_demo(isolation_level: str):
+    async with engine.connect() as conn1:
+        trans1 = await conn1.begin()
+        try:
+            await conn1.execute(text(f"SET TRANSACTION ISOLATION LEVEL {isolation_level}"))
+            print(f"\n=== Уровень изоляции: {isolation_level} ===")
+            print("[T1] Первое чтение значения price из таблицы carts")
+
+            res1 = await conn1.execute(text("SELECT price FROM carts WHERE id = 1"))
+            r1 = res1.first()[0]
+            print(f"[T1] Результат первого чтения: {r1}")
+
+            async with engine.connect() as conn2:
+                trans2 = await conn2.begin()
+                try:
+                    print("[T2] Обновляю carts.price -> 200 и фиксирую изменения")
+                    await conn2.execute(text("UPDATE carts SET price = 200 WHERE id = 1"))
+                    await trans2.commit()
+                    print("[T2] Транзакция зафиксирована")
+                except Exception as e:
+                    await trans2.rollback()
+                    print(f"[T2] Ошибка: {e}. Транзакция отменена")
+
+            print("[T1] Второе чтение значения price после фиксации изменений во второй транзакции")
+            res2 = await conn1.execute(text("SELECT price FROM carts WHERE id = 1"))
+            r2 = res2.first()[0]
+            print(f"[T1] Результат второго чтения: {r2}")
+
+            if r1 != r2:
+                print("[T1] Обнаружено non repeatable read (значение изменилось между запросами)")
+            else:
+                print("[T1] Значение не изменилось. Non repeatable read не произошло")
+
+            await trans1.commit()
+            print("[T1] Транзакция зафиксирована")
+        except Exception as e:
+            await trans1.rollback()
+            print(f"[T1] Ошибка: {e}. Транзакция отменена")
+
+
+async def main_async():
+    print("Подготовка базы данных: создание таблиц и тестовых данных")
+    await prepare()
+
+    print("\n--- Демонстрация non repeatable read (READ COMMITTED) ---")
+    await non_repeatable_demo("READ COMMITTED")
+
+    print("\n--- Демонстрация предотвращения non repeatable read (REPEATABLE READ) ---")
+    await non_repeatable_demo("REPEATABLE READ")
+
+    print("\nЗавершено")
+
+
+if __name__ == "__main__":
+    asyncio.run(main_async())
diff --git a/hw4/tx_demos/demo_phantom_read.py b/hw4/tx_demos/demo_phantom_read.py
new file mode 100644
index 00000000..a55f1497
--- /dev/null
+++ b/hw4/tx_demos/demo_phantom_read.py
@@ -0,0 +1,65 @@
+import asyncio
+from sqlalchemy import text
+from tx_demos.db_setup import prepare, engine
+
+
+async def phantom_demo(isolation_level: str):
+    async with engine.connect() as conn1:
+        trans1 = await conn1.begin()
+        try:
+            await conn1.execute(text(f"SET TRANSACTION ISOLATION LEVEL {isolation_level}"))
+            print(f"\n=== Уровень изоляции: {isolation_level} ===")
+
+            print("[T1] Выполняю первый подсчет записей, где deleted = FALSE")
+            res1 = await conn1.execute(text("SELECT COUNT(*) FROM items WHERE deleted = FALSE"))
+            c1 = res1.first()[0]
+            print(f"[T1] Количество записей при первом чтении: {c1}")
+
+            async with engine.connect() as conn2:
+                trans2 = await conn2.begin()
+                try:
+                    print("[T2] Добавляю новую запись (deleted = FALSE) и фиксирую изменения")
+                    await conn2.execute(
+                        text("INSERT INTO items (name, price, deleted) VALUES ('PhantomItem', 50.0, FALSE)")
+                    )
+                    await trans2.commit()
+                    print("[T2] Транзакция зафиксирована")
+                except Exception as e:
+                    await trans2.rollback()
+                    print(f"[T2] Ошибка: {e}. Транзакция отменена")
+
+            print("[T1] Повторяю подсчет записей, где deleted = FALSE, после фиксации второй транзакции")
+            res2 = await conn1.execute(text("SELECT COUNT(*) FROM items WHERE deleted = FALSE"))
+            c2 = res2.first()[0]
+            print(f"[T1] Количество записей при втором чтении: {c2}")
+
+            if c1 != c2:
+                print("[T1] Обнаружено phantom read (в результате появилась новая запись)")
+            else:
+                print("[T1] Phantom read не зафиксировано, результаты совпадают")
+
+            await trans1.commit()
+            print("[T1] Транзакция зафиксирована")
+        except Exception as e:
+            await trans1.rollback()
+            print(f"[T1] Ошибка: {e}. Транзакция отменена")
+
+
+async def main():
+    print("Подготовка базы данных: создание таблиц и начальных данных")
+    await prepare()
+
+    print("\n--- Демонстрация phantom read (READ COMMITTED) ---")
+    await phantom_demo("READ COMMITTED")
+
+    print("\n--- Демонстрация предотвращения phantom read (REPEATABLE READ) ---")
+    await phantom_demo("REPEATABLE READ")
+
+    print("\n--- Полная изоляция (SERIALIZABLE) ---")
+    await phantom_demo("SERIALIZABLE")
+
+    print("\nЗавершено")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())
diff --git a/hw5/__init__.py b/hw5/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/requirements.txt b/hw5/requirements.txt
new file mode 100644
index 00000000..49106c6e
--- /dev/null
+++ b/hw5/requirements.txt
@@ -0,0 +1,7 @@
+fastapi>=0.117.1
+uvicorn>=0.24.0
+
+pytest>=7.4.0
+pytest-asyncio>=0.21.0
+httpx>=0.27.2
+Faker>=37.8.0
diff --git a/hw5/shop_api/__init__.py b/hw5/shop_api/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/shop_api/main.py b/hw5/shop_api/main.py
new file mode 100644
index 00000000..952e76fc
--- /dev/null
+++ b/hw5/shop_api/main.py
@@ -0,0 +1,9 @@
+from fastapi import FastAPI
+from shop_api.routers import items, carts, chat
+
+
+app = FastAPI(title="Shop API")
+
+app.include_router(items.router)
+app.include_router(carts.router)
+app.include_router(chat.router)
\ No newline at end of file
diff --git a/hw5/shop_api/models/__init__.py b/hw5/shop_api/models/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/shop_api/routers/__init__.py b/hw5/shop_api/routers/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/shop_api/routers/carts.py b/hw5/shop_api/routers/carts.py
new file mode 100644
index 00000000..39a179be
--- /dev/null
+++ b/hw5/shop_api/routers/carts.py
@@ -0,0 +1,58 @@
+from fastapi import APIRouter, HTTPException, Query, Path, Response
+from shop_api.schemas.cart import Cart
+from shop_api.utils.cart_utils import compute_cart
+from shop_api.storage.memory import _carts, _items, _lock, _next_cart_id
+from typing import Optional, List
+
+
+router = APIRouter(prefix="/cart", tags=["carts"])
+
+@router.post("/", status_code=201)
+def create_cart(response: Response):
+    global _next_cart_id
+    with _lock:
+        cid = _next_cart_id
+        _next_cart_id += 1
+        _carts[cid] = {}
+    response.headers["Location"] = f"/cart/{cid}"
+    return {"id": cid}
+
+@router.get("/{id}", response_model=Cart)
+def get_cart(id: int = Path(..., gt=0)):
+    try:
+        return compute_cart(id)
+    except KeyError:
+        raise HTTPException(status_code=404, detail="cart not found")
+
+@router.get("/", response_model=List[Cart])
+def list_carts(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    min_quantity: Optional[int] = Query(None, ge=0),
+    max_quantity: Optional[int] = Query(None, ge=0),
+):
+    carts = []
+    for cid in sorted(_carts.keys()):
+        cart = compute_cart(cid)
+        total_qty = sum(i.quantity for i in cart.items)
+        if min_quantity is not None and total_qty < min_quantity:
+            continue
+        if max_quantity is not None and total_qty > max_quantity:
+            continue
+        if min_price is not None and cart.price < min_price:
+            continue
+        if max_price is not None and cart.price > max_price:
+            continue
+        carts.append(cart)
+    return carts[offset: offset + limit]
+
+@router.post("/{cart_id}/add/{item_id}", response_model=Cart)
+def add_item(cart_id: int, item_id: int):
+    if cart_id not in _carts:
+        raise HTTPException(status_code=404, detail="cart not found")
+    if item_id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    _carts[cart_id][item_id] = _carts[cart_id].get(item_id, 0) + 1
+    return compute_cart(cart_id)
diff --git a/hw5/shop_api/routers/chat.py b/hw5/shop_api/routers/chat.py
new file mode 100644
index 00000000..0dcf6da9
--- /dev/null
+++ b/hw5/shop_api/routers/chat.py
@@ -0,0 +1,30 @@
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+from collections import defaultdict
+import random
+import string
+from typing import Dict, List
+
+router = APIRouter(prefix="/chat", tags=["chat"])
+
+chat_rooms: Dict[str, List[WebSocket]] = defaultdict(list)
+usernames: Dict[WebSocket, str] = {}
+
+def random_username() -> str:
+    return ''.join(random.choices(string.ascii_letters + string.digits, k=8))
+
+@router.websocket("/{chat_name}")
+async def websocket_chat(websocket: WebSocket, chat_name: str):
+    await websocket.accept()
+    username = random_username()
+    usernames[websocket] = username
+    chat_rooms[chat_name].append(websocket)
+    try:
+        while True:
+            data = await websocket.receive_text()
+            message = f"{username} :: {data}"
+            for ws in chat_rooms[chat_name]:
+                if ws != websocket:
+                    await ws.send_text(message)
+    except WebSocketDisconnect:
+        chat_rooms[chat_name].remove(websocket)
+        del usernames[websocket]
diff --git a/hw5/shop_api/routers/items.py b/hw5/shop_api/routers/items.py
new file mode 100644
index 00000000..3942bd8b
--- /dev/null
+++ b/hw5/shop_api/routers/items.py
@@ -0,0 +1,81 @@
+from fastapi import APIRouter, HTTPException, Query, Response
+from shop_api.schemas.item import Item, ItemCreate
+from shop_api.storage.memory import _items, _lock, _next_item_id
+from typing import Optional, List
+
+
+router = APIRouter(prefix="/item", tags=["items"])
+
+@router.post("/", response_model=Item, status_code=201)
+def create_item(item: ItemCreate):
+    global _next_item_id
+    with _lock:
+        iid = _next_item_id
+        _next_item_id += 1
+        new_item = Item(id=iid, name=item.name, price=item.price)
+        _items[iid] = new_item
+    return new_item
+
+@router.get("/{id}", response_model=Item)
+def get_item(id: int):
+    item = _items.get(id)
+    if not item or item.deleted:
+        raise HTTPException(status_code=404, detail="item not found")
+    return item
+
+@router.get("/", response_model=List[Item])
+def list_items(
+    offset: int = Query(0, ge=0),
+    limit: int = Query(10, gt=0),
+    min_price: Optional[float] = Query(None, ge=0),
+    max_price: Optional[float] = Query(None, ge=0),
+    show_deleted: bool = Query(False),
+):
+    items = []
+    for it in _items.values():
+        if not show_deleted and it.deleted:
+            continue
+        if min_price is not None and it.price < min_price:
+            continue
+        if max_price is not None and it.price > max_price:
+            continue
+        items.append(it)
+    return items[offset: offset + limit]
+
+@router.put("/{id}", response_model=Item)
+def replace_item(id: int, item: ItemCreate):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    existing = _items[id]
+    existing.name = item.name
+    existing.price = item.price
+    _items[id] = existing
+    return existing
+
+@router.patch("/{id}", response_model=Item)
+def patch_item(id: int, patch: dict):
+    if id not in _items:
+        raise HTTPException(status_code=404, detail="item not found")
+    item = _items[id]
+    if item.deleted:
+        return Response(status_code=304)
+    allowed_keys = {"name", "price"}
+    if not set(patch.keys()).issubset(allowed_keys):
+        raise HTTPException(status_code=422)
+    if "price" in patch:
+        price = patch["price"]
+        if price is not None and price < 0:
+            raise HTTPException(status_code=422)
+        item.price = price
+    if "name" in patch:
+        item.name = patch["name"]
+    _items[id] = item
+    return item
+
+@router.delete("/{id}")
+def delete_item(id: int):
+    item = _items.get(id)
+    if not item:
+        return {"status": "ok"}
+    item.deleted = True
+    return {"status": "ok"}
\ No newline at end of file
diff --git a/hw5/shop_api/schemas/__init__.py b/hw5/shop_api/schemas/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/shop_api/schemas/cart.py b/hw5/shop_api/schemas/cart.py
new file mode 100644
index 00000000..4e3ed90c
--- /dev/null
+++ b/hw5/shop_api/schemas/cart.py
@@ -0,0 +1,14 @@
+from pydantic import BaseModel
+from typing import List
+
+
+class CartItem(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+class Cart(BaseModel):
+    id: int
+    items: List[CartItem]
+    price: float
\ No newline at end of file
diff --git a/hw5/shop_api/schemas/item.py b/hw5/shop_api/schemas/item.py
new file mode 100644
index 00000000..53021cde
--- /dev/null
+++ b/hw5/shop_api/schemas/item.py
@@ -0,0 +1,18 @@
+from pydantic import BaseModel, Field
+from typing import Optional
+
+
+class ItemBase(BaseModel):
+    name: str
+    price: float = Field(..., ge=0)
+
+class ItemCreate(ItemBase):
+    pass
+
+class Item(ItemBase):
+    id: int
+    deleted: bool = False
+
+class ItemPatch(BaseModel):
+    name: Optional[str]
+    price: Optional[float]
\ No newline at end of file
diff --git a/hw5/shop_api/storage/__init__.py b/hw5/shop_api/storage/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw5/shop_api/storage/memory.py b/hw5/shop_api/storage/memory.py
new file mode 100644
index 00000000..e769f81d
--- /dev/null
+++ b/hw5/shop_api/storage/memory.py
@@ -0,0 +1,9 @@
+from typing import Dict
+from threading import Lock
+from shop_api.schemas.item import Item
+
+_items: Dict[int, Item] = {}
+_carts: Dict[int, Dict[int, int]] = {}
+_next_item_id = 1
+_next_cart_id = 1
+_lock = Lock()
diff --git a/hw5/shop_api/utils/cart_utils.py b/hw5/shop_api/utils/cart_utils.py
new file mode 100644
index 00000000..b0c65c2e
--- /dev/null
+++ b/hw5/shop_api/utils/cart_utils.py
@@ -0,0 +1,20 @@
+from shop_api.schemas.cart import Cart, CartItem
+from shop_api.storage.memory import _carts, _items
+
+
+def compute_cart(cart_id: int) -> Cart:
+    if cart_id not in _carts:
+        raise KeyError
+    bag = _carts[cart_id]
+    items_out = []
+    total = 0.0
+    for iid, qty in bag.items():
+        item = _items.get(iid)
+        if item is None:
+            name, available = "", False
+        else:
+            name, available = item.name, not item.deleted
+        items_out.append(CartItem(id=iid, name=name, quantity=qty, available=available))
+        if item and not item.deleted:
+            total += item.price * qty
+    return Cart(id=cart_id, items=items_out, price=total)
\ No newline at end of file
diff --git a/hw5/tests/test_carts.py b/hw5/tests/test_carts.py
new file mode 100644
index 00000000..c6358576
--- /dev/null
+++ b/hw5/tests/test_carts.py
@@ -0,0 +1,137 @@
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from shop_api.routers import carts
+from shop_api.storage import memory
+from shop_api.schemas.cart import Cart, CartItem
+
+app = FastAPI()
+app.include_router(carts.router)
+client = TestClient(app)
+
+
+@pytest.fixture(autouse=True)
+def setup_memory(monkeypatch):
+    class DummyLock:
+        def __enter__(self):
+            return self
+        def __exit__(self, exc_type, exc_val, exc_tb):
+            pass
+
+    monkeypatch.setattr(memory, "_lock", DummyLock())
+
+    memory._carts.clear()
+    memory._items.clear()
+    memory._next_cart_id = 1
+    memory._next_item_id = 1
+
+    memory._items[1] = type("Item", (), {"name": "Item1", "price": 10.0, "deleted": False})()
+    yield
+    memory._carts.clear()
+    memory._items.clear()
+    memory._next_cart_id = 1
+    memory._next_item_id = 1
+
+
+def mock_compute_cart(cart_id: int):
+    if cart_id not in memory._carts:
+        raise KeyError
+    bag = memory._carts[cart_id]
+    items_out = []
+    total = 0.0
+    for iid, qty in bag.items():
+        item = memory._items[iid]
+        items_out.append(CartItem(
+            id=iid,
+            name=item.name,
+            quantity=qty,
+            available=not item.deleted
+        ))
+        if not item.deleted:
+            total += item.price * qty
+    return Cart(id=cart_id, items=items_out, price=total)
+
+
+def test_create_cart():
+    response = client.post("/cart/")
+    assert response.status_code == 201
+    data = response.json()
+    assert "id" in data
+    assert response.headers["Location"] == f"/cart/{data['id']}"
+    assert data["id"] in memory._carts
+
+
+def test_get_cart_success(monkeypatch):
+    memory._carts[1] = {}
+    monkeypatch.setattr("shop_api.utils.cart_utils.compute_cart", mock_compute_cart)
+    response = client.get("/cart/1")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["id"] == 1
+    assert isinstance(data["items"], list)
+    assert data["price"] == 0.0
+
+
+def test_get_cart_not_found():
+    response = client.get("/cart/999")
+    assert response.status_code == 404
+    assert response.json() == {"detail": "cart not found"}
+
+
+def test_list_carts_filters(monkeypatch):
+    memory._carts[1] = {1: 2}
+    memory._carts[2] = {1: 5}
+    monkeypatch.setattr("shop_api.utils.cart_utils.compute_cart", mock_compute_cart)
+
+    resp = client.get("/cart/")
+    assert resp.status_code == 200
+    assert len(resp.json()) == 2
+
+    resp = client.get("/cart/?min_price=30")
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["id"] == 2
+
+    resp = client.get("/cart/?max_price=20")
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["id"] == 1
+
+    resp = client.get("/cart/?min_quantity=3")
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["id"] == 2
+
+    resp = client.get("/cart/?max_quantity=3")
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["id"] == 1
+
+    resp = client.get("/cart/?offset=1&limit=1")
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["id"] == 2
+
+
+def test_add_item_success(monkeypatch):
+    memory._carts[1] = {}
+    monkeypatch.setattr("shop_api.utils.cart_utils.compute_cart", mock_compute_cart)
+    response = client.post("/cart/1/add/1")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["id"] == 1
+    assert data["items"][0]["quantity"] == 1
+    assert memory._carts[1][1] == 1
+
+
+def test_add_item_cart_not_found():
+    response = client.post("/cart/999/add/1")
+    assert response.status_code == 404
+    assert response.json() == {"detail": "cart not found"}
+
+
+def test_add_item_item_not_found():
+    memory._carts[1] = {}
+    response = client.post("/cart/1/add/999")
+    assert response.status_code == 404
+    assert response.json() == {"detail": "item not found"}
diff --git a/hw5/tests/test_chat_ws.py b/hw5/tests/test_chat_ws.py
new file mode 100644
index 00000000..3fa82f4a
--- /dev/null
+++ b/hw5/tests/test_chat_ws.py
@@ -0,0 +1,63 @@
+import pytest
+from fastapi import FastAPI, WebSocketDisconnect
+from fastapi.testclient import TestClient
+from shop_api.routers import chat
+
+app = FastAPI()
+app.include_router(chat.router)
+client = TestClient(app)
+
+
+@pytest.fixture(autouse=True)
+def reset_chat_rooms():
+    chat.chat_rooms.clear()
+    chat.usernames.clear()
+    yield
+    chat.chat_rooms.clear()
+    chat.usernames.clear()
+
+
+def test_random_username_length():
+    username = chat.random_username()
+    assert len(username) == 8
+    assert username.isalnum()
+
+
+def test_websocket_connect_and_disconnect():
+    with client.websocket_connect("/chat/room1") as ws:
+        ws.send_text("test")
+    assert chat.chat_rooms.get("room1") == []
+    assert len(chat.usernames) == 0
+
+
+def test_websocket_send_receive_between_two_clients():
+    with client.websocket_connect("/chat/roomX") as ws1, \
+         client.websocket_connect("/chat/roomX") as ws2:
+
+        ws1.send_text("Hello")
+        msg = ws2.receive_text()
+        assert " :: Hello" in msg
+
+        ws2.send_text("Hi there")
+        msg2 = ws1.receive_text()
+        assert " :: Hi there" in msg2
+
+    assert chat.chat_rooms.get("roomX") == []
+    assert len(chat.usernames) == 0
+
+
+def test_websocket_multiple_messages_and_disconnect():
+    with client.websocket_connect("/chat/roomY") as ws1, \
+         client.websocket_connect("/chat/roomY") as ws2:
+
+        ws1.send_text("First")
+        ws2.send_text("Second")
+
+        msg2 = ws2.receive_text()
+        assert " :: First" in msg2
+
+        msg1 = ws1.receive_text()
+        assert " :: Second" in msg1
+
+    assert chat.chat_rooms.get("roomY") == []
+    assert len(chat.usernames) == 0
diff --git a/hw5/tests/test_fastapi.py b/hw5/tests/test_fastapi.py
new file mode 100644
index 00000000..aa0d0148
--- /dev/null
+++ b/hw5/tests/test_fastapi.py
@@ -0,0 +1,20 @@
+from fastapi.testclient import TestClient
+from shop_api import main
+
+client = TestClient(main.app)
+
+
+def test_app_exists():
+    assert main.app is not None
+
+
+def test_routers_included():
+    route_paths = [route.path for route in main.app.routes]
+    assert "/item/" in route_paths or any(p.startswith("/item") for p in route_paths)
+    assert "/cart/" in route_paths or any(p.startswith("/cart") for p in route_paths)
+    assert "/chat/" in route_paths or any(p.startswith("/chat") for p in route_paths)
+
+
+def test_main_app_root_status():
+    response = client.get("/")
+    assert response.status_code in (404, 200)
diff --git a/hw5/tests/test_items.py b/hw5/tests/test_items.py
new file mode 100644
index 00000000..2893873d
--- /dev/null
+++ b/hw5/tests/test_items.py
@@ -0,0 +1,142 @@
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from shop_api.routers import items
+from shop_api.storage import memory
+
+app = FastAPI()
+app.include_router(items.router)
+client = TestClient(app)
+
+@pytest.fixture(autouse=True)
+def setup_memory(monkeypatch):
+    class DummyLock:
+        def __enter__(self):
+            return self
+        def __exit__(self, exc_type, exc_val, exc_tb):
+            pass
+
+    monkeypatch.setattr(memory, "_lock", DummyLock())
+
+    memory._items.clear()
+    memory._next_item_id = 1
+
+
+def test_create_item():
+    payload = {"name": "TestItem", "price": 100.0}
+    resp = client.post("/item/", json=payload)
+    assert resp.status_code == 201
+    data = resp.json()
+    assert data["id"] == 1
+    assert data["name"] == "TestItem"
+    assert data["price"] == 100.0
+    assert 1 in memory._items
+
+
+def test_get_item_success():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "Item1", "price": 10.0, "deleted": False})()
+    resp = client.get("/item/1")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["id"] == 1
+    assert data["name"] == "Item1"
+
+
+def test_get_item_not_found():
+    resp = client.get("/item/999")
+    assert resp.status_code == 404
+    assert resp.json() == {"detail": "item not found"}
+
+    memory._items[1] = type("Item", (), {"id": 1, "name": "Item1", "price": 10.0, "deleted": True})()
+    resp = client.get("/item/1")
+    assert resp.status_code == 404
+
+
+def test_list_items_filters():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "A", "price": 10, "deleted": False})()
+    memory._items[2] = type("Item", (), {"id": 2, "name": "B", "price": 20, "deleted": False})()
+    memory._items[3] = type("Item", (), {"id": 3, "name": "C", "price": 30, "deleted": True})()
+
+    resp = client.get("/item/")
+    data = resp.json()
+    assert len(data) == 2
+
+    resp = client.get("/item/?show_deleted=true")
+    data = resp.json()
+    assert len(data) == 3
+
+    resp = client.get("/item/?min_price=15")
+    data = resp.json()
+    assert all(d["price"] >= 15 for d in data)
+
+    resp = client.get("/item/?max_price=15")
+    data = resp.json()
+    assert all(d["price"] <= 15 for d in data)
+
+    resp = client.get("/item/?offset=1&limit=1")
+    data = resp.json()
+    assert len(data) == 1
+
+
+def test_replace_item_success():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "Old", "price": 10.0, "deleted": False})()
+    payload = {"name": "NewName", "price": 99.0}
+    resp = client.put("/item/1", json=payload)
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["name"] == "NewName"
+    assert data["price"] == 99.0
+
+
+def test_replace_item_not_found():
+    payload = {"name": "X", "price": 1.0}
+    resp = client.put("/item/999", json=payload)
+    assert resp.status_code == 404
+
+
+def test_patch_item_success():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "Old", "price": 10.0, "deleted": False})()
+    resp = client.patch("/item/1", json={"name": "New"})
+    assert resp.status_code == 200
+    assert memory._items[1].name == "New"
+
+    resp = client.patch("/item/1", json={"price": 50})
+    assert resp.status_code == 200
+    assert memory._items[1].price == 50
+
+    resp = client.patch("/item/1", json={"name": "Final", "price": 100})
+    assert resp.status_code == 200
+    assert memory._items[1].name == "Final"
+    assert memory._items[1].price == 100
+
+
+def test_patch_item_not_found():
+    resp = client.patch("/item/999", json={"name": "X"})
+    assert resp.status_code == 404
+
+
+def test_patch_item_deleted():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "X", "price": 10.0, "deleted": True})()
+    resp = client.patch("/item/1", json={"name": "Y"})
+    assert resp.status_code == 304
+
+
+def test_patch_item_invalid_field():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "X", "price": 10.0, "deleted": False})()
+    resp = client.patch("/item/1", json={"invalid": 123})
+    assert resp.status_code == 422
+
+    resp = client.patch("/item/1", json={"price": -10})
+    assert resp.status_code == 422
+
+
+def test_delete_item():
+    memory._items[1] = type("Item", (), {"id": 1, "name": "X", "price": 10.0, "deleted": False})()
+    resp = client.delete("/item/1")
+    assert resp.status_code == 200
+    assert resp.json() == {"status": "ok"}
+    assert memory._items[1].deleted is True
+
+    resp = client.delete("/item/999")
+    assert resp.status_code == 200
+    assert resp.json() == {"status": "ok"}