ShopProvider

The ShopProvider acts as the central hub for the e-commerce logic. It handles the local cart state, syncs with Firestore, and coordinates the checkout flow.

Architecture

Because the ShopProvider requires knowledge of the currently logged-in user (to sync cart and wishlist to Firestore), it should be provided using a ChangeNotifierProxyProvider if dependent on AuthProvider, or handle UID injection directly.

Core State

• List<ProductModel> _products: Global list of fetched products.
• List<CartItemModel> _cart: Items currently in the cart.
• List<String> _wishlist: Product IDs the user has liked.
• double _cartTotal: Computed value of the cart.

Cart Management

The cart is maintained locally for immediate UI updates, and asynchronously synced to the user's Firestore subcollection to persist across devices.

Methods

• addToCart(ProductModel product, int quantity)
• removeFromCart(String productId)
• updateQuantity(String productId, int newQuantity)
• clearCart()

When an item is added:

1. Check if it exists in _cart. If so, increment quantity.
2. If not, add as a new CartItemModel.
3. Calculate the new total.
4. Call notifyListeners().
5. Launch an async background task to update users/{uid}/cart in Firestore.

Checkout Flow

The processCheckout() method is complex and involves multiple steps:

1. Validation: Check stock levels for all items in _cart.
2. Order Creation: Generate an OrderModel.
3. Database Transaction:
   • Deduct stock from the products collection.
   • Write the order to the orders collection.
   • Clear the user's cart in Firestore.
4. Local State Clear: Call clearCart().
5. Notification: Trigger the Email Relay to send a confirmation email.

If any step fails, the transaction is rolled back, and the UI receives an error.