initial_commit

umkm/checkout.py

@@ -0,0 +1,60 @@
+"""Modul prosedural validasi checkout (FR-ORD-02, FR-ORD-03, FR-ORD-08).
+
+Harga diambil dari katalog, bukan dari input klien. Satu order hanya boleh
+berisi produk dari satu toko. Keranjang kosong mengembalikan total 0; penolakan
+keranjang kosong menjadi tanggung jawab pemanggil.
+"""
+
+from dataclasses import dataclass
+
+
+class CheckoutError(Exception):
+    """Kelas dasar semua kegagalan validasi checkout."""
+
+
+class ProductNotFoundError(CheckoutError):
+    pass
+
+
+class InvalidQuantityError(CheckoutError):
+    pass
+
+
+class MultiShopError(CheckoutError):
+    pass
+
+
+class InsufficientStockError(CheckoutError):
+    pass
+
+
+@dataclass(frozen=True)
+class CartItem:
+    product_id: str
+    quantity: int
+
+
+@dataclass(frozen=True)
+class CheckoutSummary:
+    shop_id: str | None
+    total_amount: int
+
+
+def validate_checkout(items, products):
+    """Validasi keranjang terhadap katalog lalu hitung total dalam rupiah."""
+    shop_id = None
+    total = 0
+    for item in items:
+        product = products.get(item.product_id)
+        if product is None:
+            raise ProductNotFoundError(item.product_id)
+        if item.quantity <= 0:
+            raise InvalidQuantityError(item.product_id)
+        if shop_id is None:
+            shop_id = product.shop_id
+        elif product.shop_id != shop_id:
+            raise MultiShopError(item.product_id)
+        if product.available < item.quantity:
+            raise InsufficientStockError(item.product_id)
+        total += product.price * item.quantity
+    return CheckoutSummary(shop_id, total)