add complex reducer logic for remove cart item

src/store/CartProvider.js

@@ -33,7 +33,34 @@ const cartReducer = (state, action) => {
     }
 
     return { items: updatedItems, totalAmount: updatedTotalAmount };
-  } else if (action.type === "REMOVE_ITEM") {
+  }
+
+  if (action.type === "REMOVE_ITEM") {
+    const existingCartItemIndex = state.items.findIndex(
+      (item) => item.id === action.id
+    );
+
+    const existingCartItem = state.items[existingCartItemIndex];
+
+    let updatedTotalAmount = state.totalAmount;
+    if (existingCartItem) {
+      updatedTotalAmount = state.totalAmount - existingCartItem.price;
+    }
+
+    let updatedItems;
+    if (existingCartItem.amount === 1) {
+      // remove the item from array because this is the last item
+      updatedItems = state.items.filter((item) => item.id !== action.id);
+    } else {
+      const updatedItem = {
+        ...existingCartItem,
+        amount: existingCartItem.amount - 1,
+      };
+      updatedItems = [...state.items];
+      updatedItems[existingCartItemIndex] = updatedItem;
+    }
+
+    return { items: updatedItems, totalAmount: updatedTotalAmount };
   }
   return defaultCartState;
 };