feat: add getTotalAmount method to Cart and refactor Purchase model to utilize it

app/Domains/Cart/Models/Cart.php

@@ -59,6 +59,18 @@ class Cart extends Model
         return $this->hasMany(CartItem::class, 'cart_id');
     }
 
+    public function getTotalAmount(): float
+    {
+        $items = $this->relationLoaded('items')
+            ? $this->getRelation('items')
+            : $this->items()->with('variant.product')->get();
+
+        return (float) $items->reduce(
+            fn (float $carry, $item): float => $carry + ((float) ($item->variant?->product?->precio ?? 0) * $item->cantidad),
+            0.0,
+        );
+    }
+
     public function addItem(int $productVariantId, int $quantity): CartItem
     {
         if ($quantity <= 0) {