Add OtpDialogService for mobile-friendly OTP authentication dialog

src/FrontOffice.Main/Utilities/CartService.cs

@@ -0,0 +1,61 @@
+namespace FrontOffice.Main.Utilities;
+
+public record CartItem(long ProductId, string Title, string ImageUrl, long UnitPrice, int Quantity)
+{
+    public long LineTotal => UnitPrice * Quantity;
+}
+
+public class CartService
+{
+    private readonly List<CartItem> _items = new();
+    public event Action? OnChange;
+
+    public IReadOnlyList<CartItem> Items => _items.AsReadOnly();
+    public long Total => _items.Sum(i => i.LineTotal);
+    public int Count => _items.Sum(i => i.Quantity);
+
+    public void Add(Product product, int quantity = 1)
+    {
+        if (quantity <= 0) return;
+        var existing = _items.FirstOrDefault(i => i.ProductId == product.Id);
+        if (existing is null)
+        {
+            _items.Add(new CartItem(product.Id, product.Title, product.ImageUrl, product.Price, quantity));
+        }
+        else
+        {
+            var idx = _items.IndexOf(existing);
+            _items[idx] = existing with { Quantity = existing.Quantity + quantity };
+        }
+        Notify();
+    }
+
+    public void UpdateQuantity(long productId, int quantity)
+    {
+        var existing = _items.FirstOrDefault(i => i.ProductId == productId);
+        if (existing is null) return;
+        if (quantity <= 0)
+        {
+            Remove(productId);
+            return;
+        }
+        var idx = _items.IndexOf(existing);
+        _items[idx] = existing with { Quantity = quantity };
+        Notify();
+    }
+
+    public void Remove(long productId)
+    {
+        _items.RemoveAll(i => i.ProductId == productId);
+        Notify();
+    }
+
+    public void Clear()
+    {
+        _items.Clear();
+        Notify();
+    }
+
+    private void Notify() => OnChange?.Invoke();
+}
+