diff --git a/hw1/app.py b/hw1/app.py
index 6107b870..2c38fecf 100644
--- a/hw1/app.py
+++ b/hw1/app.py
@@ -1,6 +1,39 @@
+import ast
+import http.client
+import math
 from typing import Any, Awaitable, Callable
 
 
+async def compute_fibonacci(num: int) -> int:
+    start = [0, 1]
+    for i in range(2, num + 1):
+        start.append(start[i - 1] + start[i - 2])
+    return start[num]
+
+
+async def compute_factorial(num: int) -> int:
+    return math.factorial(num)
+
+
+async def compute_mean(values: list[float]) -> float:
+    return sum(values) / len(values)
+
+
+async def send_error(send: Callable[[dict[str, Any]], Awaitable[None]], status: int) -> None:
+    await send({"type": "http.response.start", "status": status, "headers": []})
+    await send({"type": "http.response.body", "body": b"Error"})
+
+
+async def handle_lifespan(receive, send):
+    while True:
+        message = await receive()
+        if message["type"] == "lifespan.startup":
+            await send({"type": "lifespan.startup.complete"})
+        elif message["type"] == "lifespan.shutdown":
+            await send({"type": "lifespan.shutdown.complete"})
+            break
+
+
 async def application(
     scope: dict[str, Any],
     receive: Callable[[], Awaitable[dict[str, Any]]],
@@ -12,7 +45,73 @@ async def application(
         receive: Корутина для получения сообщений от клиента
         send: Корутина для отправки сообщений клиенту
     """
-    # TODO: Ваша реализация здесь
+    if scope["type"] == "lifespan":
+        await handle_lifespan(receive, send)
+
+    if scope["path"].startswith("/fibonacci/"):
+        await receive()
+        path: str = scope["path"]
+        path = path.rpartition("/")[2]
+        try:
+            num = int(path)
+        except ValueError:
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        if num < 0:
+            await send_error(send, http.client.BAD_REQUEST)
+            return
+        result = await compute_fibonacci(num)
+        await send({"type": "http.response.start", "status": 200, "headers": [[b"content-type", b"application/json"]]})
+        await send({"type": "http.response.body", "body": f'{{"result": {result}}}'.encode()})
+        return
+
+    if scope["path"] == "/factorial":
+        await receive()
+        query_string = scope["query_string"].decode()
+        if not query_string or "n=" not in query_string:
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        num_str = query_string.rpartition("=")[2]
+        if not num_str:
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        try:
+            num = int(num_str)
+        except ValueError:
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        if num < 0:
+            await send_error(send, http.client.BAD_REQUEST)
+            return
+        result = await compute_factorial(num)
+        await send({"type": "http.response.start", "status": 200, "headers": [[b"content-type", b"application/json"]]})
+        await send({"type": "http.response.body", "body": f'{{"result": {result}}}'.encode()})
+        return
+
+    if scope["path"] == "/mean":
+        body = await receive()
+        body_str = body["body"].decode()
+        if not body_str:
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        try:
+            lst = ast.literal_eval(body_str)
+        except (ValueError, SyntaxError):
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        if not isinstance(lst, list):
+            await send_error(send, http.client.UNPROCESSABLE_ENTITY)
+            return
+        if len(lst) == 0:
+            await send_error(send, http.client.BAD_REQUEST)
+            return
+        result = await compute_mean(lst)
+        await send({"type": "http.response.start", "status": 200, "headers": [[b"content-type", b"application/json"]]})
+        await send({"type": "http.response.body", "body": f'{{"result": {result}}}'.encode()})
+        return
+    await receive()
+    await send_error(send, http.client.NOT_FOUND)
+
 
 if __name__ == "__main__":
     import uvicorn
diff --git a/hw2/hw/shop_api/api/__init__.py b/hw2/hw/shop_api/api/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/api/cart_routes.py b/hw2/hw/shop_api/api/cart_routes.py
new file mode 100644
index 00000000..3e2d2e70
--- /dev/null
+++ b/hw2/hw/shop_api/api/cart_routes.py
@@ -0,0 +1,117 @@
+from http import HTTPStatus
+from typing import Annotated
+
+from fastapi import APIRouter, HTTPException, Query, Response
+from pydantic import NonNegativeFloat, NonNegativeInt, PositiveInt
+
+from shop_api.store.queries import (
+    add_cart,
+    add_item_to_cart,
+    get_cart,
+    get_carts,
+    get_item,
+)
+
+from .contracts import CartIdResponse, CartResponse
+
+router = APIRouter(prefix="/cart")
+
+
+@router.post(
+    "",
+    status_code=HTTPStatus.CREATED,
+)
+async def post_cart(response: Response) -> CartIdResponse:
+    entity = add_cart()
+    response.headers["location"] = f"/cart/{entity.id}"
+    return CartIdResponse(id=entity.id)
+
+
+@router.get(
+    "/{id}",
+    responses={
+        HTTPStatus.OK: {
+            "description": "Successfully returned requested cart",
+        },
+        HTTPStatus.NOT_FOUND: {
+            "description": "Cart not found",
+        },
+    },
+)
+async def get_cart_by_id(id: int) -> CartResponse:
+    entity = get_cart(id)
+    
+    if not entity:
+        raise HTTPException(
+            HTTPStatus.NOT_FOUND,
+            f"Cart with id={id} not found",
+        )
+    
+    items_dict = {}
+    for cart_item in entity.info.items:
+        item_entity = get_item(cart_item.id, include_deleted=True)
+        if item_entity:
+            items_dict[cart_item.id] = item_entity
+    
+    return CartResponse.from_entity(entity, items_dict)
+
+
+@router.get("")
+async def get_cart_list(
+    offset: Annotated[NonNegativeInt, Query()] = 0,
+    limit: Annotated[PositiveInt, Query()] = 10,
+    min_price: Annotated[NonNegativeFloat | None, Query()] = None,
+    max_price: Annotated[NonNegativeFloat | None, Query()] = None,
+    min_quantity: Annotated[NonNegativeInt | None, Query()] = None,
+    max_quantity: Annotated[NonNegativeInt | None, Query()] = None,
+) -> list[CartResponse]:
+    entities = get_carts(
+        offset=offset,
+        limit=limit,
+        min_price=min_price,
+        max_price=max_price,
+        min_quantity=min_quantity,
+        max_quantity=max_quantity,
+    )
+    
+    all_item_ids = set()
+    for cart_entity in entities:
+        for cart_item in cart_entity.info.items:
+            all_item_ids.add(cart_item.id)
+    
+    items_dict = {}
+    for item_id in all_item_ids:
+        item_entity = get_item(item_id, include_deleted=True)
+        if item_entity:
+            items_dict[item_id] = item_entity
+    
+    return [CartResponse.from_entity(e, items_dict) for e in entities]
+
+
+@router.post(
+    "/{cart_id}/add/{item_id}",
+    responses={
+        HTTPStatus.OK: {
+            "description": "Successfully added item to cart",
+        },
+        HTTPStatus.NOT_FOUND: {
+            "description": "Cart or item not found",
+        },
+    },
+)
+async def add_item_to_cart_handler(cart_id: int, item_id: int) -> CartResponse:
+    entity = add_item_to_cart(cart_id, item_id)
+    
+    if not entity:
+        raise HTTPException(
+            HTTPStatus.NOT_FOUND,
+            f"Cart with id={cart_id} or item with id={item_id} not found",
+        )
+    
+    items_dict = {}
+    for cart_item in entity.info.items:
+        item_entity = get_item(cart_item.id, include_deleted=True)
+        if item_entity:
+            items_dict[cart_item.id] = item_entity
+    
+    return CartResponse.from_entity(entity, items_dict)
diff --git a/hw2/hw/shop_api/api/chat_routes.py b/hw2/hw/shop_api/api/chat_routes.py
new file mode 100644
index 00000000..a8631b3a
--- /dev/null
+++ b/hw2/hw/shop_api/api/chat_routes.py
@@ -0,0 +1,19 @@
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+
+from shop_api.websocket_chat import chat_manager
+
+router = APIRouter()
+
+
+@router.websocket("/chat/{chat_name}")
+async def chat_endpoint(websocket: WebSocket, chat_name: str):
+    room = chat_manager.get_room(chat_name)
+    await room.connect(websocket)
+    
+    try:
+        while True:
+            message = await websocket.receive_text()
+            await room.broadcast(message, websocket)
+    except WebSocketDisconnect:
+        await room.disconnect(websocket)
+
diff --git a/hw2/hw/shop_api/api/contracts.py b/hw2/hw/shop_api/api/contracts.py
new file mode 100644
index 00000000..5d658020
--- /dev/null
+++ b/hw2/hw/shop_api/api/contracts.py
@@ -0,0 +1,89 @@
+from __future__ import annotations
+
+from pydantic import BaseModel, ConfigDict, NonNegativeFloat
+
+from shop_api.store.models import (
+    CartEntity,
+    CartItemInfo,
+    ItemEntity,
+    ItemInfo,
+    PatchItemInfo,
+)
+
+
+class ItemResponse(BaseModel):
+    id: int
+    name: str
+    price: float
+    deleted: bool = False
+
+    @staticmethod
+    def from_entity(entity: ItemEntity) -> ItemResponse:
+        return ItemResponse(
+            id=entity.id,
+            name=entity.info.name,
+            price=entity.info.price,
+            deleted=entity.info.deleted,
+        )
+
+
+class ItemRequest(BaseModel):
+    name: str
+    price: NonNegativeFloat
+
+    def as_item_info(self) -> ItemInfo:
+        return ItemInfo(name=self.name, price=self.price, deleted=False)
+
+
+class PatchItemRequest(BaseModel):
+    name: str | None = None
+    price: NonNegativeFloat | None = None
+
+    model_config = ConfigDict(extra="forbid")
+
+    def as_patch_item_info(self) -> PatchItemInfo:
+        return PatchItemInfo(name=self.name, price=self.price)
+
+
+class CartItemResponse(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+    @staticmethod
+    def from_cart_item_info(info: CartItemInfo) -> CartItemResponse:
+        return CartItemResponse(
+            id=info.id,
+            name=info.name,
+            quantity=info.quantity,
+            available=info.available,
+        )
+
+
+class CartResponse(BaseModel):
+    id: int
+    items: list[CartItemResponse]
+    price: float
+
+    @staticmethod
+    def from_entity(entity: CartEntity, items_dict: dict[int, ItemEntity]) -> CartResponse:
+        cart_items = [
+            CartItemResponse.from_cart_item_info(item) 
+            for item in entity.info.items
+        ]
+        
+        total_price = 0.0
+        for item in entity.info.items:
+            if item.id in items_dict and item.available:
+                total_price += items_dict[item.id].info.price * item.quantity
+        
+        return CartResponse(
+            id=entity.id,
+            items=cart_items,
+            price=total_price,
+        )
+
+
+class CartIdResponse(BaseModel):
+    id: int
diff --git a/hw2/hw/shop_api/api/item_routes.py b/hw2/hw/shop_api/api/item_routes.py
new file mode 100644
index 00000000..962e7f5f
--- /dev/null
+++ b/hw2/hw/shop_api/api/item_routes.py
@@ -0,0 +1,122 @@
+from http import HTTPStatus
+from typing import Annotated
+
+from fastapi import APIRouter, HTTPException, Query, Response
+from pydantic import NonNegativeFloat, NonNegativeInt, PositiveInt
+
+from shop_api.store.queries import (
+    add_item,
+    delete_item,
+    get_item,
+    get_items,
+    patch_item,
+    update_item,
+)
+
+from .contracts import ItemRequest, ItemResponse, PatchItemRequest
+
+router = APIRouter(prefix="/item")
+
+
+@router.post(
+    "",
+    status_code=HTTPStatus.CREATED,
+)
+async def post_item(item_data: ItemRequest, response: Response) -> ItemResponse:
+    entity = add_item(item_data.as_item_info())
+    response.headers["location"] = f"/item/{entity.id}"
+    return ItemResponse.from_entity(entity)
+
+
+@router.get(
+    "/{id}",
+    responses={
+        HTTPStatus.OK: {
+            "description": "Successfully returned requested item",
+        },
+        HTTPStatus.NOT_FOUND: {
+            "description": "Item not found",
+        },
+    },
+)
+async def get_item_by_id(id: int) -> ItemResponse:
+    entity = get_item(id, include_deleted=False)
+    
+    if not entity:
+        raise HTTPException(
+            HTTPStatus.NOT_FOUND,
+            f"Item with id={id} not found",
+        )
+    
+    return ItemResponse.from_entity(entity)
+
+
+@router.get("")
+async def get_item_list(
+    offset: Annotated[NonNegativeInt, Query()] = 0,
+    limit: Annotated[PositiveInt, Query()] = 10,
+    min_price: Annotated[NonNegativeFloat | None, Query()] = None,
+    max_price: Annotated[NonNegativeFloat | None, Query()] = None,
+    show_deleted: Annotated[bool, Query()] = False,
+) -> list[ItemResponse]:
+    entities = get_items(
+        offset=offset,
+        limit=limit,
+        min_price=min_price,
+        max_price=max_price,
+        show_deleted=show_deleted,
+    )
+    
+    return [ItemResponse.from_entity(e) for e in entities]
+
+
+@router.put(
+    "/{id}",
+    responses={
+        HTTPStatus.OK: {
+            "description": "Successfully updated item",
+        },
+        HTTPStatus.NOT_MODIFIED: {
+            "description": "Item not found",
+        },
+    },
+)
+async def put_item(id: int, item_data: ItemRequest) -> ItemResponse:
+    entity = update_item(id, item_data.as_item_info())
+    
+    if entity is None:
+        raise HTTPException(
+            HTTPStatus.NOT_MODIFIED,
+            f"Item with id={id} not found",
+        )
+    
+    return ItemResponse.from_entity(entity)
+
+
+@router.patch(
+    "/{id}",
+    responses={
+        HTTPStatus.OK: {
+            "description": "Successfully patched item",
+        },
+        HTTPStatus.NOT_MODIFIED: {
+            "description": "Item not found or deleted",
+        },
+    },
+)
+async def patch_item_handler(id: int, patch_data: PatchItemRequest) -> ItemResponse:
+    entity = patch_item(id, patch_data.as_patch_item_info())
+    
+    if entity is None:
+        raise HTTPException(
+            HTTPStatus.NOT_MODIFIED,
+            f"Item with id={id} not found or is deleted",
+        )
+    
+    return ItemResponse.from_entity(entity)
+
+
+@router.delete("/{id}")
+async def delete_item_handler(id: int) -> Response:
+    delete_item(id)
+    return Response(status_code=HTTPStatus.OK)
diff --git a/hw2/hw/shop_api/main.py b/hw2/hw/shop_api/main.py
index f60a8c60..16366e67 100644
--- a/hw2/hw/shop_api/main.py
+++ b/hw2/hw/shop_api/main.py
@@ -1,3 +1,11 @@
 from fastapi import FastAPI
 
+from shop_api.api.cart_routes import router as cart_router
+from shop_api.api.chat_routes import router as chat_router
+from shop_api.api.item_routes import router as item_router
+
 app = FastAPI(title="Shop API")
+
+app.include_router(item_router)
+app.include_router(cart_router)
+app.include_router(chat_router)
diff --git a/hw2/hw/shop_api/store/__init__.py b/hw2/hw/shop_api/store/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/hw2/hw/shop_api/store/models.py b/hw2/hw/shop_api/store/models.py
new file mode 100644
index 00000000..b44a6bbb
--- /dev/null
+++ b/hw2/hw/shop_api/store/models.py
@@ -0,0 +1,33 @@
+from pydantic import BaseModel
+
+
+class ItemInfo(BaseModel):
+    name: str
+    price: float
+    deleted: bool = False
+
+
+class ItemEntity(BaseModel):
+    id: int
+    info: ItemInfo
+
+
+class PatchItemInfo(BaseModel):
+    name: str | None = None
+    price: float | None = None
+
+
+class CartItemInfo(BaseModel):
+    id: int
+    name: str
+    quantity: int
+    available: bool
+
+
+class CartInfo(BaseModel):
+    items: list[CartItemInfo] = []
+
+
+class CartEntity(BaseModel):
+    id: int
+    info: CartInfo
diff --git a/hw2/hw/shop_api/store/queries.py b/hw2/hw/shop_api/store/queries.py
new file mode 100644
index 00000000..51545c9f
--- /dev/null
+++ b/hw2/hw/shop_api/store/queries.py
@@ -0,0 +1,172 @@
+from typing import Iterable
+
+from .models import (
+    CartEntity,
+    CartInfo,
+    CartItemInfo,
+    ItemEntity,
+    ItemInfo,
+    PatchItemInfo,
+)
+
+_items = dict[int, ItemInfo]()
+_carts = dict[int, CartInfo]()
+
+
+def int_id_generator() -> Iterable[int]:
+    i = 0
+    while True:
+        yield i
+        i += 1
+
+
+_item_id_generator = int_id_generator()
+_cart_id_generator = int_id_generator()
+
+
+def add_item(info: ItemInfo) -> ItemEntity:
+    _id = next(_item_id_generator)
+    _items[_id] = info
+    return ItemEntity(id=_id, info=info)
+
+
+def get_item(item_id: int, include_deleted: bool = False) -> ItemEntity | None:
+    if item_id not in _items:
+        return None
+    
+    info = _items[item_id]
+    if not include_deleted and info.deleted:
+        return None
+    
+    return ItemEntity(id=item_id, info=info)
+
+
+def get_items(
+    offset: int = 0,
+    limit: int = 10,
+    min_price: float | None = None,
+    max_price: float | None = None,
+    show_deleted: bool = False,
+) -> list[ItemEntity]:
+    result = []
+    
+    for item_id, info in _items.items():
+        if not show_deleted and info.deleted:
+            continue
+        
+        if min_price is not None and info.price < min_price:
+            continue
+        if max_price is not None and info.price > max_price:
+            continue
+        
+        result.append(ItemEntity(id=item_id, info=info))
+    
+    return result[offset:offset + limit]
+
+
+def update_item(item_id: int, info: ItemInfo) -> ItemEntity | None:
+    if item_id not in _items:
+        return None
+    
+    _items[item_id] = info
+    return ItemEntity(id=item_id, info=info)
+
+
+def patch_item(item_id: int, patch_info: PatchItemInfo) -> ItemEntity | None:
+    if item_id not in _items:
+        return None
+    
+    info = _items[item_id]
+    
+    if info.deleted:
+        return None
+    
+    if patch_info.name is not None:
+        info.name = patch_info.name
+    
+    if patch_info.price is not None:
+        info.price = patch_info.price
+    
+    return ItemEntity(id=item_id, info=info)
+
+
+def delete_item(item_id: int) -> None:
+    if item_id in _items:
+        _items[item_id].deleted = True
+
+
+def add_cart() -> CartEntity:
+    _id = next(_cart_id_generator)
+    info = CartInfo(items=[])
+    _carts[_id] = info
+    return CartEntity(id=_id, info=info)
+
+
+def get_cart(cart_id: int) -> CartEntity | None:
+    if cart_id not in _carts:
+        return None
+    
+    return CartEntity(id=cart_id, info=_carts[cart_id])
+
+
+def get_carts(
+    offset: int = 0,
+    limit: int = 10,
+    min_price: float | None = None,
+    max_price: float | None = None,
+    min_quantity: int | None = None,
+    max_quantity: int | None = None,
+) -> list[CartEntity]:
+    result = []
+    
+    for cart_id, info in _carts.items():
+        total_price = 0.0
+        total_quantity = 0
+        
+        for cart_item in info.items:
+            total_quantity += cart_item.quantity
+            
+            item_entity = get_item(cart_item.id, include_deleted=True)
+            if item_entity and cart_item.available:
+                total_price += item_entity.info.price * cart_item.quantity
+        
+        if min_price is not None and total_price < min_price:
+            continue
+        if max_price is not None and total_price > max_price:
+            continue
+        
+        if min_quantity is not None and total_quantity < min_quantity:
+            continue
+        if max_quantity is not None and total_quantity > max_quantity:
+            continue
+        
+        result.append(CartEntity(id=cart_id, info=info))
+    
+    return result[offset:offset + limit]
+
+
+def add_item_to_cart(cart_id: int, item_id: int) -> CartEntity | None:
+    if cart_id not in _carts:
+        return None
+    
+    cart_info = _carts[cart_id]
+    
+    item_entity = get_item(item_id, include_deleted=True)
+    if not item_entity:
+        return None
+    
+    for cart_item in cart_info.items:
+        if cart_item.id == item_id:
+            cart_item.quantity += 1
+            cart_item.available = not item_entity.info.deleted
+            return CartEntity(id=cart_id, info=cart_info)
+    
+    cart_item = CartItemInfo(
+        id=item_id,
+        name=item_entity.info.name,
+        quantity=1,
+        available=not item_entity.info.deleted,
+    )
+    cart_info.items.append(cart_item)
+    
+    return CartEntity(id=cart_id, info=cart_info)
diff --git a/hw2/hw/shop_api/websocket_chat.py b/hw2/hw/shop_api/websocket_chat.py
new file mode 100644
index 00000000..2646360b
--- /dev/null
+++ b/hw2/hw/shop_api/websocket_chat.py
@@ -0,0 +1,55 @@
+import random
+from collections import defaultdict
+
+from fastapi import WebSocket
+
+
+class ChatRoom:
+    def __init__(self):
+        self.connections: dict[WebSocket, str] = {}
+    
+    async def connect(self, ws: WebSocket) -> str:
+        await ws.accept()
+        username = self._generate_username()
+        self.connections[ws] = username
+        return username
+    
+    async def disconnect(self, ws: WebSocket) -> None:
+        if ws in self.connections:
+            del self.connections[ws]
+    
+    async def broadcast(self, message: str, sender_ws: WebSocket) -> None:
+        username = self.connections.get(sender_ws, "Unknown")
+        formatted_message = f"{username} :: {message}"
+        
+        for ws in self.connections:
+            await ws.send_text(formatted_message)
+    
+    def _generate_username(self) -> str:
+        adjectives = [
+            "Happy", "Brave", "Calm", "Dreamy", "Eager",
+            "Fancy", "Gentle", "Jolly", "Kind", "Lively",
+            "Mighty", "Nice", "Proud", "Quick", "Smart",
+            "Swift", "Wise", "Witty", "Young", "Zesty"
+        ]
+        
+        nouns = [
+            "Panda", "Tiger", "Eagle", "Dolphin", "Fox",
+            "Wolf", "Bear", "Lion", "Owl", "Hawk",
+            "Dragon", "Phoenix", "Unicorn", "Griffin", "Raven",
+            "Falcon", "Panther", "Lynx", "Otter", "Shark"
+        ]
+        
+        return f"{random.choice(adjectives)}{random.choice(nouns)}"
+
+
+class ChatManager:
+    def __init__(self):
+        self.rooms: dict[str, ChatRoom] = defaultdict(ChatRoom)
+    
+    def get_room(self, chat_name: str) -> ChatRoom:
+        return self.rooms[chat_name]
+
+
+chat_manager = ChatManager()
+
diff --git a/lecture4/.gitignore b/lecture4/.gitignore
new file mode 100644
index 00000000..79f7a6f7
--- /dev/null
+++ b/lecture4/.gitignore
@@ -0,0 +1,5 @@
+vendor
+docs
+internal/repository/db.go
+internal/repository/models.go
+internal/repository/queries.sql.go
diff --git a/lecture4/Dockerfile b/lecture4/Dockerfile
new file mode 100644
index 00000000..06ff8ef9
--- /dev/null
+++ b/lecture4/Dockerfile
@@ -0,0 +1,29 @@
+FROM golang:1.24-alpine AS builder
+
+WORKDIR /app
+
+COPY go.mod ./
+RUN go mod download
+
+COPY . .
+
+RUN go run github.com/sqlc-dev/sqlc/cmd/sqlc@latest generate
+
+RUN go run github.com/swaggo/swag/cmd/swag@latest init -g cmd/app/main.go
+
+RUN go mod tidy
+
+RUN CGO_ENABLED=0 GOOS=linux go build -o main ./cmd/app
+
+FROM alpine:latest
+
+WORKDIR /app
+
+RUN apk --no-cache add ca-certificates
+
+COPY --from=builder /app/main .
+
+EXPOSE 8080
+
+CMD ["./main"]
+
diff --git a/lecture4/cmd/app/main.go b/lecture4/cmd/app/main.go
new file mode 100644
index 00000000..86153e06
--- /dev/null
+++ b/lecture4/cmd/app/main.go
@@ -0,0 +1,72 @@
+package main
+
+import (
+	"database/sql"
+	"log"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	_ "github.com/lib/pq"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	swaggerFiles "github.com/swaggo/files"
+	ginSwagger "github.com/swaggo/gin-swagger"
+	"lecture4/internal/api"
+	"lecture4/internal/config"
+
+	_ "lecture4/docs"
+)
+
+// @title Shop API
+// @version 1.0
+// @description REST API для интернет магазина с товарами и корзинами
+// @host localhost:8080
+// @BasePath /
+func main() {
+	cfg := config.Load()
+
+	// Подключение к базе данных с retry логикой
+	var db *sql.DB
+	var err error
+	for i := 0; i < 10; i++ {
+		db, err = sql.Open("postgres", cfg.DatabaseURL)
+		if err == nil {
+			err = db.Ping()
+			if err == nil {
+				break
+			}
+		}
+		log.Printf("Failed to connect to database, retrying in 2 seconds... (%d/10)", i+1)
+		time.Sleep(2 * time.Second)
+	}
+	if err != nil {
+		log.Fatalf("Failed to connect to database after 10 attempts: %v", err)
+	}
+	defer db.Close()
+
+	log.Println("Successfully connected to database")
+
+	router := gin.Default()
+
+	router.GET("/metrics", gin.WrapH(promhttp.Handler()))
+
+	router.GET("/swagger/*any", ginSwagger.WrapHandler(swaggerFiles.Handler))
+
+	handler := api.NewHandler(db)
+
+	router.POST("/item", handler.PostItem)
+	router.GET("/item/:id", handler.GetItemByID)
+	router.GET("/item", handler.GetItems)
+	router.PUT("/item/:id", handler.PutItem)
+	router.PATCH("/item/:id", handler.PatchItem)
+	router.DELETE("/item/:id", handler.DeleteItem)
+
+	router.POST("/cart", handler.PostCart)
+	router.GET("/cart/:id", handler.GetCartByID)
+	router.GET("/cart", handler.GetCarts)
+	router.POST("/cart/:cart_id/add/:item_id", handler.AddItemToCart)
+
+	log.Printf("Starting server on port %s", cfg.Port)
+	if err := router.Run(":" + cfg.Port); err != nil {
+		log.Fatalf("Failed to start server: %v", err)
+	}
+}
diff --git a/lecture4/ddoser.py b/lecture4/ddoser.py
new file mode 100644
index 00000000..b238885e
--- /dev/null
+++ b/lecture4/ddoser.py
@@ -0,0 +1,157 @@
+from concurrent.futures import ThreadPoolExecutor, as_completed
+
+import requests
+from faker import Faker
+
+faker = Faker()
+
+
+def create_items():
+    """Создает товары в магазине"""
+    for _ in range(500):
+        product_name = faker.word().capitalize() + " " + faker.word()
+        price = round(faker.random.uniform(10.0, 9999.99), 2)
+        
+        response = requests.post(
+            "http://localhost:8080/item",
+            json={
+                "name": product_name,
+                "price": price,
+            },
+        )
+        print(f"Create item: {response.status_code}")
+
+
+def get_items():
+    """Получает список товаров"""
+    for _ in range(500):
+        offset = faker.random_int(0, 50)
+        limit = faker.random_int(5, 50)
+        
+        response = requests.get(
+            "http://localhost:8080/item",
+            params={
+                "offset": offset,
+                "limit": limit,
+            },
+        )
+        print(f"Get items: {response.status_code}")
+
+
+def get_item_by_id():
+    """Получает товар по ID"""
+    for _ in range(500):
+        item_id = faker.random_int(1, 100)
+        
+        response = requests.get(
+            f"http://localhost:8080/item/{item_id}",
+        )
+        print(f"Get item {item_id}: {response.status_code}")
+
+
+def update_items():
+    """Обновляет товары"""
+    for _ in range(300):
+        item_id = faker.random_int(1, 50)
+        product_name = faker.word().capitalize() + " Updated"
+        price = round(faker.random.uniform(10.0, 9999.99), 2)
+        
+        response = requests.put(
+            f"http://localhost:8080/item/{item_id}",
+            json={
+                "name": product_name,
+                "price": price,
+            },
+        )
+        print(f"Update item {item_id}: {response.status_code}")
+
+
+def create_carts():
+    """Создает корзины"""
+    for _ in range(300):
+        response = requests.post(
+            "http://localhost:8080/cart",
+        )
+        print(f"Create cart: {response.status_code}")
+
+
+def get_carts():
+    """Получает список корзин"""
+    for _ in range(300):
+        offset = faker.random_int(0, 50)
+        limit = faker.random_int(5, 30)
+        
+        response = requests.get(
+            "http://localhost:8080/cart",
+            params={
+                "offset": offset,
+                "limit": limit,
+            },
+        )
+        print(f"Get carts: {response.status_code}")
+
+
+def add_items_to_cart():
+    """Добавляет товары в корзины"""
+    for _ in range(400):
+        cart_id = faker.random_int(1, 100)
+        item_id = faker.random_int(1, 100)
+        
+        response = requests.post(
+            f"http://localhost:8080/cart/{cart_id}/add/{item_id}",
+        )
+        print(f"Add item {item_id} to cart {cart_id}: {response.status_code}")
+
+
+def get_cart_by_id():
+    """Получает корзину по ID"""
+    for _ in range(400):
+        cart_id = faker.random_int(1, 100)
+        
+        response = requests.get(
+            f"http://localhost:8080/cart/{cart_id}",
+        )
+        print(f"Get cart {cart_id}: {response.status_code}")
+
+
+if __name__ == "__main__":
+    with ThreadPoolExecutor(max_workers=20) as executor:
+        futures = {}
+
+        # Создание товаров
+        for i in range(10):
+            futures[executor.submit(create_items)] = f"create-items-{i}"
+
+        # Получение списков товаров
+        for i in range(10):
+            futures[executor.submit(get_items)] = f"get-items-{i}"
+
+        # Получение товаров по ID
+        for i in range(10):
+            futures[executor.submit(get_item_by_id)] = f"get-item-by-id-{i}"
+
+        # Обновление товаров
+        for i in range(5):
+            futures[executor.submit(update_items)] = f"update-items-{i}"
+
+        # Создание корзин
+        for i in range(8):
+            futures[executor.submit(create_carts)] = f"create-carts-{i}"
+
+        # Получение списков корзин
+        for i in range(8):
+            futures[executor.submit(get_carts)] = f"get-carts-{i}"
+
+        # Добавление товаров в корзины
+        for i in range(12):
+            futures[executor.submit(add_items_to_cart)] = f"add-items-to-cart-{i}"
+
+        # Получение корзин по ID
+        for i in range(12):
+            futures[executor.submit(get_cart_by_id)] = f"get-cart-by-id-{i}"
+
+        for future in as_completed(futures):
+            print(f"✓ Completed {futures[future]}")
+
+    print("\n🎯 DDoS test completed!")
+
diff --git a/lecture4/docker-compose.shop.yml b/lecture4/docker-compose.shop.yml
new file mode 100644
index 00000000..efa57a00
--- /dev/null
+++ b/lecture4/docker-compose.shop.yml
@@ -0,0 +1,61 @@
+services:
+  postgres:
+    build:
+      context: ./migrations
+      dockerfile: Dockerfile
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: shop
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    ports:
+      - "5433:5432"
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+    restart: always
+
+  app:
+    build:
+      context: .
+      dockerfile: ./Dockerfile
+    environment:
+      DATABASE_URL: postgres://postgres:postgres@postgres:5432/shop?sslmode=disable
+      PORT: "8080"
+    ports:
+      - "8080:8080"
+    depends_on:
+      postgres:
+        condition: service_healthy
+    restart: always
+
+  prometheus:
+    build:
+      context: ./settings/prometheus
+      dockerfile: Dockerfile
+    volumes:
+      - prometheus_data:/prometheus
+    ports:
+      - "9090:9090"
+    restart: always
+
+  grafana:
+    image: grafana/grafana:latest
+    ports:
+      - "3000:3000"
+    environment:
+      GF_SECURITY_ADMIN_USER: admin
+      GF_SECURITY_ADMIN_PASSWORD: admin
+    volumes:
+      - grafana_data:/var/lib/grafana
+      - ./settings/grafana/provisioning:/etc/grafana/provisioning:ro
+    restart: always
+
+volumes:
+  postgres_data:
+  prometheus_data:
+  grafana_data:
+
diff --git a/lecture4/go.mod b/lecture4/go.mod
new file mode 100644
index 00000000..be32c00a
--- /dev/null
+++ b/lecture4/go.mod
@@ -0,0 +1,59 @@
+module lecture4
+
+go 1.24
+
+require (
+	github.com/gin-gonic/gin v1.10.0
+	github.com/lib/pq v1.10.9
+	github.com/prometheus/client_golang v1.20.5
+	github.com/swaggo/files v1.0.1
+	github.com/swaggo/gin-swagger v1.6.0
+	github.com/swaggo/swag v1.16.4
+)
+
+require (
+	github.com/KyleBanks/depth v1.2.1 // indirect
+	github.com/PuerkitoBio/purell v1.1.1 // indirect
+	github.com/PuerkitoBio/urlesc v0.0.0-20170810143723-de5bf2ad4578 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/bytedance/sonic v1.11.6 // indirect
+	github.com/bytedance/sonic/loader v0.1.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/cloudwego/base64x v0.1.4 // indirect
+	github.com/cloudwego/iasm v0.2.0 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.3 // indirect
+	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/go-openapi/jsonpointer v0.19.5 // indirect
+	github.com/go-openapi/jsonreference v0.19.6 // indirect
+	github.com/go-openapi/spec v0.20.4 // indirect
+	github.com/go-openapi/swag v0.19.15 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-playground/validator/v10 v10.20.0 // indirect
+	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/josharian/intern v1.0.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/compress v1.17.9 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	github.com/mailru/easyjson v0.7.6 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.2 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.55.0 // indirect
+	github.com/prometheus/procfs v0.15.1 // indirect
+	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
+	github.com/ugorji/go/codec v1.2.12 // indirect
+	golang.org/x/arch v0.8.0 // indirect
+	golang.org/x/crypto v0.24.0 // indirect
+	golang.org/x/net v0.26.0 // indirect
+	golang.org/x/sys v0.22.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d // indirect
+	google.golang.org/protobuf v1.34.2 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/lecture4/go.sum b/lecture4/go.sum
new file mode 100644
index 00000000..faf66918
--- /dev/null
+++ b/lecture4/go.sum
@@ -0,0 +1,191 @@
+github.com/KyleBanks/depth v1.2.1 h1:5h8fQADFrWtarTdtDudMmGsC7GPbOAu6RVB3ffsVFHc=
+github.com/KyleBanks/depth v1.2.1/go.mod h1:jzSb9d0L43HxTQfT+oSA1EEp2q+ne2uh6XgeJcm8brE=
+github.com/PuerkitoBio/purell v1.1.1 h1:WEQqlqaGbrPkxLJWfBwQmfEAE1Z7ONdDLqrN38tNFfI=
+github.com/PuerkitoBio/purell v1.1.1/go.mod h1:c11w/QuzBsJSee3cPx9rAFu61PvFxuPbtSwDGJws/X0=
+github.com/PuerkitoBio/urlesc v0.0.0-20170810143723-de5bf2ad4578 h1:d+Bc7a5rLufV/sSk/8dngufqelfh6jnri85riMAaF/M=
+github.com/PuerkitoBio/urlesc v0.0.0-20170810143723-de5bf2ad4578/go.mod h1:uGdkoq3SwY9Y+13GIhn11/XLaGBb4BfwItxLd5jeuXE=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/bytedance/sonic v1.11.6 h1:oUp34TzMlL+OY1OUWxHqsdkgC/Zfc85zGqw9siXjrc0=
+github.com/bytedance/sonic v1.11.6/go.mod h1:LysEHSvpvDySVdC2f87zGWf6CIKJcAvqab1ZaiQtds4=
+github.com/bytedance/sonic/loader v0.1.1 h1:c+e5Pt1k/cy5wMveRDyk2X4B9hF4g7an8N3zCYjJFNM=
+github.com/bytedance/sonic/loader v0.1.1/go.mod h1:ncP89zfokxS5LZrJxl5z0UJcsk4M4yY2JpfqGeCtNLU=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/cloudwego/base64x v0.1.4 h1:jwCgWpFanWmN8xoIUHa2rtzmkd5J2plF/dnLS6Xd/0Y=
+github.com/cloudwego/base64x v0.1.4/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
+github.com/cloudwego/iasm v0.2.0 h1:1KNIy1I1H9hNNFEEH3DVnI4UujN+1zjpuk6gwHLTssg=
+github.com/cloudwego/iasm v0.2.0/go.mod h1:8rXZaNYT2n95jn+zTI1sDr+IgcD2GVs0nlbbQPiEFhY=
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gabriel-vasile/mimetype v1.4.3 h1:in2uUcidCuFcDKtdcBxlR0rJ1+fsokWf+uqxgUFjbI0=
+github.com/gabriel-vasile/mimetype v1.4.3/go.mod h1:d8uq/6HKRL6CGdk+aubisF/M5GcPfT7nKyLpA0lbSSk=
+github.com/gin-contrib/gzip v0.0.6 h1:NjcunTcGAj5CO1gn4N8jHOSIeRFHIbn51z6K+xaN4d4=
+github.com/gin-contrib/gzip v0.0.6/go.mod h1:QOJlmV2xmayAjkNS2Y8NQsMneuRShOU/kjovCXNuzzk=
+github.com/gin-contrib/sse v0.1.0 h1:Y/yl/+YNO8GZSjAhjMsSuLt29uWRFHdHYUb5lYOV9qE=
+github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm+fLHvGI=
+github.com/gin-gonic/gin v1.10.0 h1:nTuyha1TYqgedzytsKYqna+DfLos46nTv2ygFy86HFU=
+github.com/gin-gonic/gin v1.10.0/go.mod h1:4PMNQiOhvDRa013RKVbsiNwoyezlm2rm0uX/T7kzp5Y=
+github.com/go-openapi/jsonpointer v0.19.3/go.mod h1:Pl9vOtqEWErmShwVjC8pYs9cog34VGT37dQOVbmoatg=
+github.com/go-openapi/jsonpointer v0.19.5 h1:gZr+CIYByUqjcgeLXnQu2gHYQC9o73G2XUeOFYEICuY=
+github.com/go-openapi/jsonpointer v0.19.5/go.mod h1:Pl9vOtqEWErmShwVjC8pYs9cog34VGT37dQOVbmoatg=
+github.com/go-openapi/jsonreference v0.19.6 h1:UBIxjkht+AWIgYzCDSv2GN+E/togfwXUJFRTWhl2Jjs=
+github.com/go-openapi/jsonreference v0.19.6/go.mod h1:diGHMEHg2IqXZGKxqyvWdfWU/aim5Dprw5bqpKkTvns=
+github.com/go-openapi/spec v0.20.4 h1:O8hJrt0UMnhHcluhIdUgCLRWyM2x7QkBXRvOs7m+O1M=
+github.com/go-openapi/spec v0.20.4/go.mod h1:faYFR1CvsJZ0mNsmsphTMSoRrNV3TEDoAM7FOEWeq8I=
+github.com/go-openapi/swag v0.19.5/go.mod h1:POnQmlKehdgb5mhVOsnJFsivZCEZ/vjK9gh66Z9tfKk=
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diff --git a/lecture4/graphana.jpg b/lecture4/graphana.jpg
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diff --git a/lecture4/graphana_ddos.jpg b/lecture4/graphana_ddos.jpg
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diff --git a/lecture4/internal/api/handlers.go b/lecture4/internal/api/handlers.go
new file mode 100644
index 00000000..c499e2a1
--- /dev/null
+++ b/lecture4/internal/api/handlers.go
@@ -0,0 +1,574 @@
+package api
+
+import (
+	"context"
+	"database/sql"
+	"net/http"
+	"strconv"
+
+	"lecture4/internal/repository"
+
+	"github.com/gin-gonic/gin"
+	"github.com/lib/pq"
+)
+
+type Handler struct {
+	queries *repository.Queries
+	db      *sql.DB
+}
+
+func NewHandler(db *sql.DB) *Handler {
+	return &Handler{
+		queries: repository.New(db),
+		db:      db,
+	}
+}
+
+// Обобщенная функция для конверсии любого типа Row с полями ID, Name, Price, Deleted в ItemResponse
+func rowToItemResponse(id int32, name string, price float64, deleted bool) ItemResponse {
+	return ItemResponse{
+		ID:      id,
+		Name:    name,
+		Price:   price,
+		Deleted: deleted,
+	}
+}
+
+// cartItemsToResponse преобразует список GetCartItemsRow в CartItemResponse
+func cartItemsToResponse(items []repository.GetCartItemsRow) []CartItemResponse {
+	result := make([]CartItemResponse, 0, len(items))
+	for _, ci := range items {
+		result = append(result, CartItemResponse{
+			ID:        ci.ItemID,
+			Name:      ci.Name,
+			Quantity:  ci.Quantity,
+			Available: !ci.Deleted,
+		})
+	}
+	return result
+}
+
+// cartItemsForCartsToResponse преобразует список GetCartItemsForCartsRow в CartItemResponse
+func cartItemsForCartsToResponse(items []repository.GetCartItemsForCartsRow) []CartItemResponse {
+	result := make([]CartItemResponse, 0, len(items))
+	for _, ci := range items {
+		result = append(result, CartItemResponse{
+			ID:        ci.ItemID,
+			Name:      ci.Name,
+			Quantity:  ci.Quantity,
+			Available: !ci.Deleted,
+		})
+	}
+	return result
+}
+
+// buildCartResponse строит полный ответ с информацией о корзине
+func (h *Handler) buildCartResponse(ctx context.Context, cartID int32) (CartResponse, error) {
+	cartItems, err := h.queries.GetCartItems(ctx, cartID)
+	if err != nil {
+		return CartResponse{}, err
+	}
+
+	totalPrice, err := h.queries.GetCartTotalPrice(ctx, cartID)
+	if err != nil {
+		return CartResponse{}, err
+	}
+
+	items := cartItemsToResponse(cartItems)
+
+	return CartResponse{
+		ID:    cartID,
+		Items: items,
+		Price: totalPrice,
+	}, nil
+}
+
+// PostItem godoc
+// @Summary Создать товар
+// @Description Создает новый товар
+// @Tags items
+// @Accept json
+// @Produce json
+// @Param item body ItemRequest true "Данные товара"
+// @Success 201 {object} ItemResponse
+// @Failure 400 {object} ErrorResponse
+// @Router /item [post]
+func (h *Handler) PostItem(c *gin.Context) {
+	var req ItemRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	item, err := h.queries.CreateItem(c.Request.Context(), repository.CreateItemParams{
+		Name:  req.Name,
+		Price: req.Price,
+	})
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.Header("Location", "/item/"+strconv.Itoa(int(item.ID)))
+	c.JSON(http.StatusCreated, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+}
+
+// GetItemByID godoc
+// @Summary Получить товар по ID
+// @Description Получает товар по его ID
+// @Tags items
+// @Produce json
+// @Param id path int true "ID товара"
+// @Success 200 {object} ItemResponse
+// @Failure 404 {object} ErrorResponse
+// @Router /item/{id} [get]
+func (h *Handler) GetItemByID(c *gin.Context) {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid item ID"})
+		return
+	}
+
+	item, err := h.queries.GetItem(c.Request.Context(), int32(id))
+	if err != nil {
+		if err == sql.ErrNoRows {
+			c.JSON(http.StatusNotFound, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	if item.Deleted {
+		c.JSON(http.StatusNotFound, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found"})
+		return
+	}
+
+	c.JSON(http.StatusOK, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+}
+
+// GetItems godoc
+// @Summary Получить список товаров
+// @Description Получает список товаров с фильтрацией и пагинацией
+// @Tags items
+// @Produce json
+// @Param offset query int false "Смещение" default(0)
+// @Param limit query int false "Лимит" default(10)
+// @Param min_price query number false "Минимальная цена"
+// @Param max_price query number false "Максимальная цена"
+// @Param show_deleted query bool false "Показывать удаленные" default(false)
+// @Success 200 {array} ItemResponse
+// @Router /item [get]
+func (h *Handler) GetItems(c *gin.Context) {
+	offset, _ := strconv.Atoi(c.DefaultQuery("offset", "0"))
+	limit, _ := strconv.Atoi(c.DefaultQuery("limit", "10"))
+	showDeleted := c.DefaultQuery("show_deleted", "false") == "true"
+
+	var minPrice, maxPrice sql.NullFloat64
+	if minPriceStr := c.Query("min_price"); minPriceStr != "" {
+		if val, err := strconv.ParseFloat(minPriceStr, 64); err == nil {
+			minPrice = sql.NullFloat64{Float64: val, Valid: true}
+		}
+	}
+	if maxPriceStr := c.Query("max_price"); maxPriceStr != "" {
+		if val, err := strconv.ParseFloat(maxPriceStr, 64); err == nil {
+			maxPrice = sql.NullFloat64{Float64: val, Valid: true}
+		}
+	}
+
+	items, err := h.queries.GetItems(c.Request.Context(), repository.GetItemsParams{
+		Limit:       int32(limit),
+		Offset:      int32(offset),
+		ShowDeleted: showDeleted,
+		MinPrice:    minPrice,
+		MaxPrice:    maxPrice,
+	})
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	result := make([]ItemResponse, 0, len(items))
+	for _, item := range items {
+		result = append(result, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
+// PutItem godoc
+// @Summary Обновить товар
+// @Description Полностью обновляет существующий товар
+// @Tags items
+// @Accept json
+// @Produce json
+// @Param id path int true "ID товара"
+// @Param item body ItemRequest true "Данные товара"
+// @Success 200 {object} ItemResponse
+// @Failure 304 {object} ErrorResponse
+// @Failure 400 {object} ErrorResponse
+// @Router /item/{id} [put]
+func (h *Handler) PutItem(c *gin.Context) {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid item ID"})
+		return
+	}
+
+	var req ItemRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	// Проверяем, существует ли товар
+	existingItem, err := h.queries.GetItem(c.Request.Context(), int32(id))
+	if err != nil {
+		if err == sql.ErrNoRows {
+			c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	if existingItem.Deleted {
+		c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found"})
+		return
+	}
+
+	item, err := h.queries.UpdateItem(c.Request.Context(), repository.UpdateItemParams{
+		ID:    int32(id),
+		Name:  req.Name,
+		Price: req.Price,
+	})
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+}
+
+// PatchItem godoc
+// @Summary Частично обновить товар
+// @Description Частично обновляет существующий товар (кроме поля deleted)
+// @Tags items
+// @Accept json
+// @Produce json
+// @Param id path int true "ID товара"
+// @Param item body PatchItemRequest true "Данные для обновления"
+// @Success 200 {object} ItemResponse
+// @Failure 304 {object} ErrorResponse
+// @Failure 400 {object} ErrorResponse
+// @Router /item/{id} [patch]
+func (h *Handler) PatchItem(c *gin.Context) {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid item ID"})
+		return
+	}
+
+	var req PatchItemRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	if req.Name != nil && req.Price != nil {
+		item, err := h.queries.PatchItemBoth(c.Request.Context(), repository.PatchItemBothParams{
+			ID:    int32(id),
+			Name:  *req.Name,
+			Price: *req.Price,
+		})
+		if err != nil {
+			if err == sql.ErrNoRows {
+				c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found or is deleted"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+	} else if req.Name != nil {
+		item, err := h.queries.PatchItemName(c.Request.Context(), repository.PatchItemNameParams{
+			ID:   int32(id),
+			Name: *req.Name,
+		})
+		if err != nil {
+			if err == sql.ErrNoRows {
+				c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found or is deleted"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+	} else if req.Price != nil {
+		item, err := h.queries.PatchItemPrice(c.Request.Context(), repository.PatchItemPriceParams{
+			ID:    int32(id),
+			Price: *req.Price,
+		})
+		if err != nil {
+			if err == sql.ErrNoRows {
+				c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found or is deleted"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, rowToItemResponse(item.ID, item.Name, item.Price, item.Deleted))
+	} else {
+		// Нет полей для обновления - возвращаем текущий товар
+		existingItem, err := h.queries.GetItem(c.Request.Context(), int32(id))
+		if err != nil {
+			if err == sql.ErrNoRows {
+				c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found or is deleted"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+			return
+		}
+		if existingItem.Deleted {
+			c.JSON(http.StatusNotModified, ErrorResponse{Message: "Item with id=" + c.Param("id") + " not found or is deleted"})
+			return
+		}
+		c.JSON(http.StatusOK, rowToItemResponse(existingItem.ID, existingItem.Name, existingItem.Price, existingItem.Deleted))
+	}
+}
+
+// DeleteItem godoc
+// @Summary Удалить товар
+// @Description Помечает товар как удаленный
+// @Tags items
+// @Param id path int true "ID товара"
+// @Success 200
+// @Router /item/{id} [delete]
+func (h *Handler) DeleteItem(c *gin.Context) {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid item ID"})
+		return
+	}
+
+	err = h.queries.DeleteItem(c.Request.Context(), int32(id))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.Status(http.StatusOK)
+}
+
+// PostCart godoc
+// @Summary Создать корзину
+// @Description Создает новую пустую корзину
+// @Tags carts
+// @Produce json
+// @Success 201 {object} CartIdResponse
+// @Router /cart [post]
+func (h *Handler) PostCart(c *gin.Context) {
+	cart, err := h.queries.CreateCart(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.Header("Location", "/cart/"+strconv.Itoa(int(cart.ID)))
+	c.JSON(http.StatusCreated, CartIdResponse{ID: cart.ID})
+}
+
+// GetCartByID godoc
+// @Summary Получить корзину по ID
+// @Description Получает корзину по её ID с расчетом общей стоимости
+// @Tags carts
+// @Produce json
+// @Param id path int true "ID корзины"
+// @Success 200 {object} CartResponse
+// @Failure 404 {object} ErrorResponse
+// @Router /cart/{id} [get]
+func (h *Handler) GetCartByID(c *gin.Context) {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid cart ID"})
+		return
+	}
+
+	cart, err := h.queries.GetCart(c.Request.Context(), int32(id))
+	if err != nil {
+		if err == sql.ErrNoRows {
+			c.JSON(http.StatusNotFound, ErrorResponse{Message: "Cart with id=" + c.Param("id") + " not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	cartResponse, err := h.buildCartResponse(c.Request.Context(), cart.ID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, cartResponse)
+}
+
+// GetCarts godoc
+// @Summary Получить список корзин
+// @Description Получает список корзин с фильтрацией и пагинацией
+// @Tags carts
+// @Produce json
+// @Param offset query int false "Смещение" default(0)
+// @Param limit query int false "Лимит" default(10)
+// @Param min_price query number false "Минимальная цена"
+// @Param max_price query number false "Максимальная цена"
+// @Param min_quantity query int false "Минимальное количество товаров"
+// @Param max_quantity query int false "Максимальное количество товаров"
+// @Success 200 {array} CartResponse
+// @Router /cart [get]
+func (h *Handler) GetCarts(c *gin.Context) {
+	offset, _ := strconv.Atoi(c.DefaultQuery("offset", "0"))
+	limit, _ := strconv.Atoi(c.DefaultQuery("limit", "10"))
+
+	var minPrice, maxPrice sql.NullFloat64
+	var minQuantity, maxQuantity sql.NullInt32
+
+	if minPriceStr := c.Query("min_price"); minPriceStr != "" {
+		if val, err := strconv.ParseFloat(minPriceStr, 64); err == nil {
+			minPrice = sql.NullFloat64{Float64: val, Valid: true}
+		}
+	}
+	if maxPriceStr := c.Query("max_price"); maxPriceStr != "" {
+		if val, err := strconv.ParseFloat(maxPriceStr, 64); err == nil {
+			maxPrice = sql.NullFloat64{Float64: val, Valid: true}
+		}
+	}
+	if minQtyStr := c.Query("min_quantity"); minQtyStr != "" {
+		if val, err := strconv.Atoi(minQtyStr); err == nil {
+			minQuantity = sql.NullInt32{Int32: int32(val), Valid: true}
+		}
+	}
+	if maxQtyStr := c.Query("max_quantity"); maxQtyStr != "" {
+		if val, err := strconv.Atoi(maxQtyStr); err == nil {
+			maxQuantity = sql.NullInt32{Int32: int32(val), Valid: true}
+		}
+	}
+
+	carts, err := h.queries.GetAllCartsWithStats(c.Request.Context(), repository.GetAllCartsWithStatsParams{
+		Limit:       int32(limit),
+		Offset:      int32(offset),
+		MinPrice:    minPrice,
+		MaxPrice:    maxPrice,
+		MinQuantity: minQuantity,
+		MaxQuantity: maxQuantity,
+	})
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	cartIDs := make([]int32, len(carts))
+	for i, cart := range carts {
+		cartIDs[i] = cart.ID
+	}
+
+	var allCartItems []repository.GetCartItemsForCartsRow
+	if len(cartIDs) > 0 {
+		allCartItems, err = h.queries.GetCartItemsForCarts(c.Request.Context(), cartIDs)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+			return
+		}
+	}
+
+	// Группируем товары по корзинам
+	cartItemsMap := make(map[int32][]repository.GetCartItemsForCartsRow)
+	for _, ci := range allCartItems {
+		cartItemsMap[ci.CartID] = append(cartItemsMap[ci.CartID], ci)
+	}
+
+	result := make([]CartResponse, 0, len(carts))
+	for _, cart := range carts {
+		items := cartItemsForCartsToResponse(cartItemsMap[cart.ID])
+
+		result = append(result, CartResponse{
+			ID:    cart.ID,
+			Items: items,
+			Price: cart.TotalPrice,
+		})
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
+// AddItemToCart godoc
+// @Summary Добавить товар в корзину
+// @Description Добавляет товар в корзину или увеличивает его количество
+// @Tags carts
+// @Produce json
+// @Param cart_id path int true "ID корзины"
+// @Param item_id path int true "ID товара"
+// @Success 200 {object} CartResponse
+// @Failure 404 {object} ErrorResponse
+// @Router /cart/{cart_id}/add/{item_id} [post]
+func (h *Handler) AddItemToCart(c *gin.Context) {
+	cartID, err := strconv.Atoi(c.Param("cart_id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid cart ID"})
+		return
+	}
+
+	itemID, err := strconv.Atoi(c.Param("item_id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Message: "Invalid item ID"})
+		return
+	}
+
+	// Проверяем существование корзины
+	_, err = h.queries.GetCart(c.Request.Context(), int32(cartID))
+	if err != nil {
+		if err == sql.ErrNoRows {
+			c.JSON(http.StatusNotFound, ErrorResponse{Message: "Cart with id=" + c.Param("cart_id") + " or item with id=" + c.Param("item_id") + " not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	// Проверяем существование товара
+	_, err = h.queries.GetItem(c.Request.Context(), int32(itemID))
+	if err != nil {
+		if err == sql.ErrNoRows {
+			c.JSON(http.StatusNotFound, ErrorResponse{Message: "Cart with id=" + c.Param("cart_id") + " or item with id=" + c.Param("item_id") + " not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	// Добавляем товар в корзину
+	_, err = h.queries.AddItemToCart(c.Request.Context(), repository.AddItemToCartParams{
+		CartID: int32(cartID),
+		ItemID: int32(itemID),
+	})
+	if err != nil {
+		// Проверяем ошибку foreign key constraint
+		if pqErr, ok := err.(*pq.Error); ok {
+			if pqErr.Code == "23503" { // foreign_key_violation
+				c.JSON(http.StatusNotFound, ErrorResponse{Message: "Cart with id=" + c.Param("cart_id") + " or item with id=" + c.Param("item_id") + " not found"})
+				return
+			}
+		}
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	// Возвращаем обновленную корзину
+	cartResponse, err := h.buildCartResponse(c.Request.Context(), int32(cartID))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{Message: err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, cartResponse)
+}
diff --git a/lecture4/internal/api/models.go b/lecture4/internal/api/models.go
new file mode 100644
index 00000000..39f3c60a
--- /dev/null
+++ b/lecture4/internal/api/models.go
@@ -0,0 +1,46 @@
+package api
+
+// ItemRequest представляет запрос на создание или обновление товара
+type ItemRequest struct {
+	Name  string  `json:"name" binding:"required" example:"Молоко"`
+	Price float64 `json:"price" binding:"required,gte=0" example:"159.99"`
+}
+
+// PatchItemRequest представляет запрос на частичное обновление товара
+type PatchItemRequest struct {
+	Name  *string  `json:"name,omitempty" example:"Молоко обновленное"`
+	Price *float64 `json:"price,omitempty" example:"169.99"`
+}
+
+// ItemResponse представляет ответ с информацией о товаре
+type ItemResponse struct {
+	ID      int32   `json:"id" example:"1"`
+	Name    string  `json:"name" example:"Молоко"`
+	Price   float64 `json:"price" example:"159.99"`
+	Deleted bool    `json:"deleted" example:"false"`
+}
+
+// CartItemResponse представляет товар в корзине
+type CartItemResponse struct {
+	ID        int32  `json:"id" example:"1"`
+	Name      string `json:"name" example:"Молоко"`
+	Quantity  int32  `json:"quantity" example:"3"`
+	Available bool   `json:"available" example:"true"`
+}
+
+// CartResponse представляет ответ с информацией о корзине
+type CartResponse struct {
+	ID    int32              `json:"id" example:"1"`
+	Items []CartItemResponse `json:"items"`
+	Price float64            `json:"price" example:"234.40"`
+}
+
+// CartIdResponse представляет ответ с ID корзины
+type CartIdResponse struct {
+	ID int32 `json:"id" example:"1"`
+}
+
+// ErrorResponse представляет ответ с ошибкой
+type ErrorResponse struct {
+	Message string `json:"detail" example:"Item not found"`
+}
diff --git a/lecture4/internal/config/config.go b/lecture4/internal/config/config.go
new file mode 100644
index 00000000..a5e212b7
--- /dev/null
+++ b/lecture4/internal/config/config.go
@@ -0,0 +1,27 @@
+package config
+
+import (
+	"os"
+)
+
+type Config struct {
+	DatabaseURL string
+	Port        string
+}
+
+func Load() *Config {
+	databaseURL := os.Getenv("DATABASE_URL")
+	if databaseURL == "" {
+		databaseURL = "postgres://postgres:postgres@localhost:5432/shop?sslmode=disable"
+	}
+
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+
+	return &Config{
+		DatabaseURL: databaseURL,
+		Port:        port,
+	}
+}
diff --git a/lecture4/internal/repository/queries.sql b/lecture4/internal/repository/queries.sql
new file mode 100644
index 00000000..e17071dd
--- /dev/null
+++ b/lecture4/internal/repository/queries.sql
@@ -0,0 +1,111 @@
+-- Items queries
+
+-- name: CreateItem :one
+INSERT INTO items (name, price, deleted)
+VALUES (sqlc.arg('name'), sqlc.arg('price')::float8, FALSE)
+RETURNING id, name, price::float8 AS price, deleted, created_at;
+
+-- name: GetItem :one
+SELECT id, name, price::float8 AS price, deleted, created_at FROM items WHERE id = $1;
+
+-- name: GetItems :many
+SELECT id, name, price::float8 AS price, deleted, created_at FROM items
+WHERE 
+    (sqlc.arg(show_deleted)::boolean = TRUE OR deleted = FALSE)
+    AND (sqlc.narg('min_price')::float8 IS NULL OR price >= sqlc.narg('min_price'))
+    AND (sqlc.narg('max_price')::float8 IS NULL OR price <= sqlc.narg('max_price'))
+ORDER BY id
+LIMIT $1 OFFSET $2;
+
+-- name: UpdateItem :one
+UPDATE items
+SET name = sqlc.arg('name'), price = sqlc.arg('price')::float8
+WHERE id = sqlc.arg('id')
+RETURNING id, name, price::float8 AS price, deleted, created_at;
+
+-- name: PatchItemName :one
+UPDATE items
+SET name = sqlc.arg('name')
+WHERE id = sqlc.arg('id') AND deleted = FALSE
+RETURNING id, name, price::float8 AS price, deleted, created_at;
+
+-- name: PatchItemPrice :one
+UPDATE items
+SET price = sqlc.arg('price')::float8
+WHERE id = sqlc.arg('id') AND deleted = FALSE
+RETURNING id, name, price::float8 AS price, deleted, created_at;
+
+-- name: PatchItemBoth :one
+UPDATE items
+SET name = sqlc.arg('name'), price = sqlc.arg('price')::float8
+WHERE id = sqlc.arg('id') AND deleted = FALSE
+RETURNING id, name, price::float8 AS price, deleted, created_at;
+
+-- name: DeleteItem :exec
+UPDATE items
+SET deleted = TRUE
+WHERE id = $1;
+
+-- Carts queries
+
+-- name: CreateCart :one
+INSERT INTO carts DEFAULT VALUES
+RETURNING *;
+
+-- name: GetCart :one
+SELECT * FROM carts WHERE id = $1;
+
+-- name: GetCarts :many
+SELECT * FROM carts
+ORDER BY id
+LIMIT $1 OFFSET $2;
+
+-- name: GetCartItems :many
+SELECT ci.cart_id, ci.item_id, ci.quantity, i.name, i.price::float8 AS price, i.deleted
+FROM cart_items ci
+JOIN items i ON ci.item_id = i.id
+WHERE ci.cart_id = $1
+ORDER BY ci.item_id;
+
+-- name: GetCartItemsForCarts :many
+SELECT ci.cart_id, ci.item_id, ci.quantity, i.name, i.price::float8 AS price, i.deleted
+FROM cart_items ci
+JOIN items i ON ci.item_id = i.id
+WHERE ci.cart_id = ANY($1::int[])
+ORDER BY ci.cart_id, ci.item_id;
+
+-- name: AddItemToCart :one
+INSERT INTO cart_items (cart_id, item_id, quantity)
+VALUES ($1, $2, 1)
+ON CONFLICT (cart_id, item_id)
+DO UPDATE SET quantity = cart_items.quantity + 1
+RETURNING *;
+
+-- name: GetCartTotalPrice :one
+SELECT COALESCE(SUM(ci.quantity * i.price), 0)::float8 as total
+FROM cart_items ci
+JOIN items i ON ci.item_id = i.id
+WHERE ci.cart_id = $1 AND i.deleted = FALSE;
+
+-- name: GetCartTotalQuantity :one
+SELECT COALESCE(SUM(ci.quantity), 0)::int8 as total
+FROM cart_items ci
+WHERE ci.cart_id = $1;
+
+-- name: GetAllCartsWithStats :many
+SELECT 
+    c.id,
+    COALESCE(SUM(ci.quantity), 0)::int8 as total_quantity,
+    COALESCE(SUM(CASE WHEN i.deleted = FALSE THEN ci.quantity * i.price ELSE 0 END), 0)::float8 as total_price
+FROM carts c
+LEFT JOIN cart_items ci ON c.id = ci.cart_id
+LEFT JOIN items i ON ci.item_id = i.id
+GROUP BY c.id
+HAVING 
+    (sqlc.narg('min_price')::float8 IS NULL OR COALESCE(SUM(CASE WHEN i.deleted = FALSE THEN ci.quantity * i.price ELSE 0 END), 0) >= sqlc.narg('min_price'))
+    AND (sqlc.narg('max_price')::float8 IS NULL OR COALESCE(SUM(CASE WHEN i.deleted = FALSE THEN ci.quantity * i.price ELSE 0 END), 0) <= sqlc.narg('max_price'))
+    AND (sqlc.narg('min_quantity')::int IS NULL OR COALESCE(SUM(ci.quantity), 0) >= sqlc.narg('min_quantity'))
+    AND (sqlc.narg('max_quantity')::int IS NULL OR COALESCE(SUM(ci.quantity), 0) <= sqlc.narg('max_quantity'))
+ORDER BY c.id
+LIMIT $1 OFFSET $2;
+
diff --git a/lecture4/migrations/Dockerfile b/lecture4/migrations/Dockerfile
new file mode 100644
index 00000000..a0623feb
--- /dev/null
+++ b/lecture4/migrations/Dockerfile
@@ -0,0 +1,6 @@
+FROM postgres:15-alpine
+
+COPY shop_init.sql /docker-entrypoint-initdb.d/init.sql
+
+EXPOSE 5432
+
diff --git a/lecture4/migrations/shop_init.sql b/lecture4/migrations/shop_init.sql
new file mode 100644
index 00000000..77be4e62
--- /dev/null
+++ b/lecture4/migrations/shop_init.sql
@@ -0,0 +1,42 @@
+-- Создание схемы базы данных для Shop API
+DROP TABLE IF EXISTS cart_items CASCADE;
+DROP TABLE IF EXISTS carts CASCADE;
+DROP TABLE IF EXISTS items CASCADE;
+
+-- Таблица товаров
+CREATE TABLE items (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(255) NOT NULL,
+    price NUMERIC(10, 2) NOT NULL CHECK (price >= 0),
+    deleted BOOLEAN NOT NULL DEFAULT FALSE,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Таблица корзин
+CREATE TABLE carts (
+    id SERIAL PRIMARY KEY,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Таблица связи корзин и товаров
+CREATE TABLE cart_items (
+    cart_id INTEGER NOT NULL REFERENCES carts(id) ON DELETE CASCADE,
+    item_id INTEGER NOT NULL REFERENCES items(id) ON DELETE CASCADE,
+    quantity INTEGER NOT NULL CHECK (quantity > 0),
+    PRIMARY KEY (cart_id, item_id)
+);
+
+-- Индексы для оптимизации запросов
+CREATE INDEX idx_items_deleted ON items(deleted);
+CREATE INDEX idx_items_price ON items(price);
+CREATE INDEX idx_cart_items_cart_id ON cart_items(cart_id);
+CREATE INDEX idx_cart_items_item_id ON cart_items(item_id);
+
+-- Вставка тестовых данных для проверки
+INSERT INTO items (name, price, deleted) VALUES
+    ('Туалетная бумага "Поцелуй", рулон', 50.00, FALSE),
+    ('Золотая цепочка "Abendsonne"', 15000.00, FALSE),
+    ('Молоко "Буреночка" 1л.', 159.99, FALSE),
+    ('Хлеб белый', 45.50, FALSE),
+    ('Удаленный товар', 100.00, TRUE);
+
diff --git a/lecture4/requirements.txt b/lecture4/requirements.txt
new file mode 100644
index 00000000..4a296010
--- /dev/null
+++ b/lecture4/requirements.txt
@@ -0,0 +1,2 @@
+requests==2.31.0
+faker==20.1.0
diff --git a/lecture4/settings/grafana/provisioning/dashboards/shop-api.json b/lecture4/settings/grafana/provisioning/dashboards/shop-api.json
new file mode 100644
index 00000000..a7b09c5a
--- /dev/null
+++ b/lecture4/settings/grafana/provisioning/dashboards/shop-api.json
@@ -0,0 +1,419 @@
+{
+  "annotations": {
+    "list": []
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": null,
+  "links": [],
+  "liveNow": false,
+  "panels": [
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "drawStyle": "line",
+            "fillOpacity": 10,
+            "gradientMode": "none",
+            "hideFrom": {
+              "tooltip": false,
+              "viz": false,
+              "legend": false
+            },
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "never",
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          },
+          "unit": "short"
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 12,
+        "x": 0,
+        "y": 0
+      },
+      "id": 1,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "prometheus"
+          },
+          "expr": "rate(promhttp_metric_handler_requests_total[1m])",
+          "refId": "A"
+        }
+      ],
+      "title": "HTTP Requests Rate",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              },
+              {
+                "color": "yellow",
+                "value": 50
+              },
+              {
+                "color": "red",
+                "value": 80
+              }
+            ]
+          },
+          "unit": "percent"
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 12,
+        "x": 12,
+        "y": 0
+      },
+      "id": 2,
+      "options": {
+        "orientation": "auto",
+        "reduceOptions": {
+          "values": false,
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": ""
+        },
+        "showThresholdLabels": false,
+        "showThresholdMarkers": true
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "prometheus"
+          },
+          "expr": "rate(process_cpu_seconds_total[1m]) * 100",
+          "refId": "A"
+        }
+      ],
+      "title": "CPU Usage",
+      "type": "gauge"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "drawStyle": "line",
+            "fillOpacity": 10,
+            "gradientMode": "none",
+            "hideFrom": {
+              "tooltip": false,
+              "viz": false,
+              "legend": false
+            },
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "never",
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          },
+          "unit": "bytes"
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 12,
+        "x": 0,
+        "y": 8
+      },
+      "id": 3,
+      "options": {
+        "legend": {
+          "calcs": [
+            "mean",
+            "lastNotNull",
+            "max"
+          ],
+          "displayMode": "table",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "prometheus"
+          },
+          "expr": "process_resident_memory_bytes",
+          "refId": "A"
+        }
+      ],
+      "title": "Memory Usage",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "drawStyle": "line",
+            "fillOpacity": 10,
+            "gradientMode": "none",
+            "hideFrom": {
+              "tooltip": false,
+              "viz": false,
+              "legend": false
+            },
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "never",
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          },
+          "unit": "short"
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 12,
+        "x": 12,
+        "y": 8
+      },
+      "id": 4,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "prometheus"
+          },
+          "expr": "go_goroutines",
+          "refId": "A"
+        }
+      ],
+      "title": "Goroutines",
+      "type": "timeseries"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "prometheus"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          },
+          "unit": "short"
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 24,
+        "x": 0,
+        "y": 16
+      },
+      "id": 5,
+      "options": {
+        "displayMode": "gradient",
+        "minVizHeight": 10,
+        "minVizWidth": 0,
+        "orientation": "horizontal",
+        "reduceOptions": {
+          "values": false,
+          "calcs": [
+            "lastNotNull"
+          ],
+          "fields": ""
+        },
+        "showUnfilled": true
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "prometheus"
+          },
+          "expr": "sum by (code) (promhttp_metric_handler_requests_total)",
+          "refId": "A"
+        }
+      ],
+      "title": "HTTP Status Codes",
+      "type": "bargauge"
+    }
+  ],
+  "refresh": "5s",
+  "schemaVersion": 38,
+  "style": "dark",
+  "tags": [
+    "shop-api",
+    "golang"
+  ],
+  "templating": {
+    "list": []
+  },
+  "time": {
+    "from": "now-15m",
+    "to": "now"
+  },
+  "timepicker": {},
+  "timezone": "",
+  "title": "Shop API Monitoring",
+  "uid": "shop-api-dashboard",
+  "version": 1,
+  "weekStart": ""
+}
diff --git a/lecture4/settings/prometheus/Dockerfile b/lecture4/settings/prometheus/Dockerfile
new file mode 100644
index 00000000..a1e0c986
--- /dev/null
+++ b/lecture4/settings/prometheus/Dockerfile
@@ -0,0 +1,11 @@
+FROM prom/prometheus:latest
+
+COPY prometheus.yml /etc/prometheus/prometheus.yml
+
+EXPOSE 9090
+
+CMD ["--config.file=/etc/prometheus/prometheus.yml", \
+     "--storage.tsdb.path=/prometheus", \
+     "--web.console.libraries=/usr/share/prometheus/console_libraries", \
+     "--web.console.templates=/usr/share/prometheus/consoles"]
+
diff --git a/lecture4/settings/prometheus/prometheus.yml b/lecture4/settings/prometheus/prometheus.yml
new file mode 100644
index 00000000..bcde8d83
--- /dev/null
+++ b/lecture4/settings/prometheus/prometheus.yml
@@ -0,0 +1,11 @@
+global:
+  scrape_interval: 10s
+  evaluation_interval: 10s
+
+scrape_configs:
+  - job_name: shop-api
+    metrics_path: /metrics
+    static_configs:
+      - targets:
+          - app:8080
+
diff --git a/lecture4/sqlc.yaml b/lecture4/sqlc.yaml
new file mode 100644
index 00000000..ad5f458a
--- /dev/null
+++ b/lecture4/sqlc.yaml
@@ -0,0 +1,12 @@
+version: "2"
+sql:
+  - engine: "postgresql"
+    queries: "internal/repository/queries.sql"
+    schema: "migrations/shop_init.sql"
+    gen:
+      go:
+        package: "repository"
+        out: "internal/repository"
+        emit_json_tags: true
+        emit_interface: false
+        emit_exact_table_names: false