乡镇商家聚合配送系统怎么搭建：四端订单与结算验收

from dataclasses import dataclass
from decimal import Decimal


class InvalidTransition(Exception):
    pass


ALLOWED = {
    ("CREATED", "PAID"),
    ("PAID", "ACCEPTED"),
    ("ACCEPTED", "READY"),
    ("READY", "PICKED_UP"),
    ("PICKED_UP", "DELIVERED"),
    ("DELIVERED", "PARTIAL_REFUNDED"),
}

EVENT_TARGET = {
    "PAY": "PAID",
    "ACCEPT": "ACCEPTED",
    "READY": "READY",
    "PICKUP": "PICKED_UP",
    "DELIVER": "DELIVERED",
    "PART_REFUND": "PARTIAL_REFUNDED",
}


@dataclass
class Order:
    order_id: str
    status: str = "CREATED"
    goods: Decimal = Decimal("30.00")
    delivery: Decimal = Decimal("5.00")
    commission: Decimal = Decimal("3.00")
    merchant: Decimal = Decimal("0.00")
    rider: Decimal = Decimal("0.00")
    platform: Decimal = Decimal("0.00")


class Service:
    def __init__(self):
        self.order = Order("O1001")
        self.event_ids = set()
        self.idem_keys = set()
        self.entries = []

    def apply(self, event_id, idem_key, event_type):
        if event_id in self.event_ids or idem_key in self.idem_keys:
            return {"applied": False, "reason": "DUPLICATE", "status": self.order.status}

        target = EVENT_TARGET[event_type]
        if (self.order.status, target) not in ALLOWED:
            raise InvalidTransition(f"{self.order.status} -> {target}")

        if target == "DELIVERED":
            merchant_amount = self.order.goods - self.order.commission
            batch = [
                ("MERCHANT", "SALE", merchant_amount),
                ("RIDER", "SALE", self.order.delivery),
                ("PLATFORM", "SALE", self.order.commission),
            ]
        elif target == "PARTIAL_REFUNDED":
            batch = [
                ("MERCHANT", "REFUND", Decimal("-3.60")),
                ("PLATFORM", "COMMISSION_REVERSAL", Decimal("-0.40")),
            ]
        else:
            batch = []

        for account, kind, amount in batch:
            self.entries.append((event_id, account, kind, amount))
            if account == "MERCHANT":
                self.order.merchant += amount
            elif account == "RIDER":
                self.order.rider += amount
            else:
                self.order.platform += amount

        self.order.status = target
        self.event_ids.add(event_id)
        self.idem_keys.add(idem_key)
        return {
            "applied": True,
            "status": target,
            "entries": len(self.entries),
            "balances": self.balances(),
        }

    def balances(self):
        return {
            "merchant": str(self.order.merchant),
            "rider": str(self.order.rider),
            "platform": str(self.order.platform),
        }


if __name__ == "__main__":
    service = Service()
    steps = [
        ("e1", "k1", "PAY"),
        ("e2", "k2", "ACCEPT"),
        ("e3", "k3", "READY"),
        ("e4", "k4", "PICKUP"),
        ("e5", "k5", "DELIVER"),
    ]
    for step in steps:
        service.apply(*step)

    print(service.apply("e5", "k5", "DELIVER"))
    print(service.apply("e6", "k6", "PART_REFUND"))

    try:
        service.apply("e7", "k7", "DELIVER")
    except InvalidTransition as exc:
        print("INVALID", exc)

    assert service.order.merchant == Decimal("23.40")
    assert service.order.rider == Decimal("5.00")
    assert service.order.platform == Decimal("2.60")
    assert service.order.merchant + service.order.rider + service.order.platform == Decimal("31.00")