feat(orders): implement timezone-aware timestamp handling

backend/DTOs/ReplenishmentOrder/ReplenishmentOrderDTO.cs

@@ -4,7 +4,7 @@ public class ReplenishmentOrderResponseDto
 {
     public Guid OrderId { get; set; }
     public string Isbn { get; set; }
-    public DateOnly OrderDate { get; set; }
+    public DateTime OrderDate { get; set; }
     public int Quantity { get; set; }
     public string Status { get; set; }
 }

backend/Migrations/004_DateToTimestamp.sql

@@ -0,0 +1,19 @@
+-- Migration to change DATE columns to TIMESTAMPTZ for timezone support
+-- This ensures proper handling of timezone offsets in frontend/backend
+-- TIMESTAMPTZ stores timestamps in UTC internally and converts based on timezone
+
+-- Alter customer_order table
+ALTER TABLE customer_order 
+ALTER COLUMN order_date TYPE TIMESTAMPTZ 
+USING order_date::TIMESTAMPTZ;
+
+ALTER TABLE customer_order 
+ALTER COLUMN order_date SET DEFAULT CURRENT_TIMESTAMP;
+
+-- Alter replenishment_order table
+ALTER TABLE replenishment_order 
+ALTER COLUMN order_date TYPE TIMESTAMPTZ 
+USING order_date::TIMESTAMPTZ;
+
+ALTER TABLE replenishment_order 
+ALTER COLUMN order_date SET DEFAULT CURRENT_TIMESTAMP;

backend/Models/ReplenishmentOrder.cs

@@ -4,7 +4,7 @@ public class ReplenishmentOrder
 {
     public Guid OrderId { get; set; }
     public string Isbn { get; set; }
-    public DateOnly OrderDate { get; set; }
+    public DateTime OrderDate { get; set; }
     public int Quantity { get; set; }
     public string Status { get; set; }
 }

backend/Program.cs

@@ -17,6 +17,9 @@
 var builder = WebApplication.CreateBuilder(args);
 Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
 
+// Configure Npgsql to read timestamps as UTC
+AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", false);
+
 // Load DB Connection
 var connectionString = Environment.GetEnvironmentVariable("CONNECTION_STRING");
 if (string.IsNullOrEmpty(connectionString))
@@ -41,6 +44,8 @@
     .AddJsonOptions(options =>
     {
         options.JsonSerializerOptions.PropertyNamingPolicy = System.Text.Json.JsonNamingPolicy.CamelCase;
+        // Ensure DateTime values are serialized as UTC with 'Z' suffix
+        options.JsonSerializerOptions.Converters.Add(new System.Text.Json.Serialization.JsonStringEnumConverter());
     });
 
 
@@ -96,7 +101,7 @@
             ValidIssuer = cfg["Jwt:Issuer"],
             ValidAudience = cfg["Jwt:Audience"],
             IssuerSigningKey = new SymmetricSecurityKey(
                 Encoding.UTF8.GetBytes(cfg["Jwt:Key"])
             )
         };
     });

backend/Repositories/CustomerOrder/CustomerOrderRepository.cs

@@ -28,12 +28,18 @@ INSERT INTO customer_order_item(order_id, isbn, quantity, price)
     public async Task<IEnumerable<CustomerOrder>> GetOrdersAsync(Guid userId)
     {
         const string sql = @"
-            SELECT order_id as OrderId, u_id as UserId, order_date::timestamp as OrderDate, total_price as TotalPrice 
+            SELECT order_id as OrderId, u_id as UserId, order_date AT TIME ZONE 'UTC' as OrderDate, total_price as TotalPrice 
             FROM customer_order 
             WHERE u_id = @UserId 
             ORDER BY order_date DESC;
         ";
-        return (await _db.QueryAsync<CustomerOrder>(sql, new { UserId = userId })).ToList();
+        var orders = await _db.QueryAsync<CustomerOrder>(sql, new { UserId = userId });
+        // Ensure DateTime is marked as UTC
+        foreach (var order in orders)
+        {
+            order.OrderDate = DateTime.SpecifyKind(order.OrderDate, DateTimeKind.Utc);
+        }
+        return orders.ToList();
     }
 
     public async Task<IEnumerable<CustomerOrderItem>> GetOrderItemsAsync(Guid orderId)

backend/Repositories/ReplenishmentOrder/ReplenishmentOrderRepository.cs

@@ -15,17 +15,28 @@ public ReplenishmentOrderRepository(IDbConnection db)
 
     public async Task<IEnumerable<ReplenishmentOrder>> GetAllAsync()
     {
-        return await _db.QueryAsync<ReplenishmentOrder>(
+        var orders = await _db.QueryAsync<ReplenishmentOrder>(
             "SELECT * FROM replenishment_order ORDER BY order_date DESC;"
         );
+        // Ensure DateTime is marked as UTC
+        foreach (var order in orders)
+        {
+            order.OrderDate = DateTime.SpecifyKind(order.OrderDate, DateTimeKind.Utc);
+        }
+        return orders;
     }
 
     public async Task<ReplenishmentOrder?> GetByIdAsync(Guid orderId)
     {
-        return await _db.QuerySingleOrDefaultAsync<ReplenishmentOrder>(
+        var order = await _db.QuerySingleOrDefaultAsync<ReplenishmentOrder>(
             "SELECT * FROM replenishment_order WHERE order_id = @OrderId;",
             new { OrderId = orderId }
         );
+        if (order != null)
+        {
+            order.OrderDate = DateTime.SpecifyKind(order.OrderDate, DateTimeKind.Utc);
+        }
+        return order;
     }
 
     public async Task ConfirmAsync(Guid orderId)

frontend/app/admin/home/page.tsx

@@ -125,10 +125,14 @@ export default function AdminDashboard() {
 
   const formatDate = (dateString: string) => {
     const date = new Date(dateString);
-    return date.toLocaleDateString("en-US", {
+    return date.toLocaleString(undefined, {
       year: "numeric",
       month: "short",
       day: "numeric",
+      hour: "2-digit",
+      minute: "2-digit",
+      timeZoneName: "short",
+      timeZone: Intl.DateTimeFormat().resolvedOptions().timeZone,
     });
   };
 

frontend/app/admin/publisher-orders/page.tsx

@@ -91,10 +91,14 @@ export default function PublisherOrdersPage() {
 
   const formatDate = (dateString: string) => {
     const date = new Date(dateString);
-    return date.toLocaleDateString("en-US", {
+    return date.toLocaleString(undefined, {
       year: "numeric",
       month: "long",
       day: "numeric",
+      hour: "2-digit",
+      minute: "2-digit",
+      timeZoneName: "short",
+      timeZone: Intl.DateTimeFormat().resolvedOptions().timeZone,
     });
   };
 

frontend/app/user/orders/page.tsx

@@ -64,21 +64,25 @@ export default function OrdersPage() {
 
   const formatDate = (dateString: string) => {
     const date = new Date(dateString);
-    return date.toLocaleDateString("en-US", {
+    return date.toLocaleDateString(undefined, {
       year: "numeric",
       month: "long",
       day: "numeric",
+      timeZone: Intl.DateTimeFormat().resolvedOptions().timeZone,
     });
   };
 
   const formatDateTime = (dateString: string) => {
     const date = new Date(dateString);
-    return date.toLocaleString("en-US", {
+    return date.toLocaleString(undefined, {
       year: "numeric",
       month: "long",
       day: "numeric",
       hour: "2-digit",
       minute: "2-digit",
+      second: "2-digit",
+      timeZoneName: "short",
+      timeZone: Intl.DateTimeFormat().resolvedOptions().timeZone,
     });
   };