"""Payment gateway abstraction with idempotent callbacks.

Payments never talk to a concrete gateway directly; the gateway is selected
from configuration and isolated behind an interface.
"""
from typing import Protocol

from django.conf import settings


class PaymentGatewayInterface(Protocol):
    def request_payment(self, amount, currency, order_number: str, callback_url: str) -> dict:
        """Return {'authority': str, 'redirect_url': str}."""
        ...

    def verify(self, authority: str, amount) -> dict:
        """Return {'transaction_id': str, 'status': 'success'|'failed'|'cancelled'}."""
        ...


class MockGateway:
    def request_payment(self, amount, currency, order_number: str, callback_url: str) -> dict:
        return {
            "authority": f"MOCK-AUTH-{order_number}",
            "redirect_url": f"{callback_url}?authority=MOCK-AUTH-{order_number}",
        }

    def verify(self, authority: str, amount) -> dict:
        return {"transaction_id": f"MOCK-TXN-{authority}", "status": "success"}


def get_gateway() -> PaymentGatewayInterface:
    if settings.PAYMENT_GATEWAY_PROVIDER == "mock":
        return MockGateway()
    # Real gateways (GatewayA, GatewayB, ...) are selected here.
    return MockGateway()