校园外卖小程序选SaaS还是自研：用订单状态机与异常验收判断

FLOW = {
    'CREATED': {'PAID', 'CLOSED'},
    'PAID': {'ACCEPTED', 'REFUNDING'},
    'ACCEPTED': {'COOKED', 'REFUNDING'},
    'COOKED': {'PICKED_UP'},
    'PICKED_UP': {'HUB_RECEIVED'},
    'HUB_RECEIVED': {'SORTED'},
    'SORTED': {'DELIVERED'},
    'DELIVERED': {'SETTLED'},
    'REFUNDING': {'CLOSED'},
    'SETTLED': set(),
    'CLOSED': set(),
}

def can_move(src, dst, ctx=None):
    ctx = ctx or {}
    if dst not in FLOW.get(src, set()):
        return False
    if dst == 'PAID' and not ctx.get('paid'):
        return False
    return True

def move(src, dst, ctx=None):
    if not can_move(src, dst, ctx):
        raise ValueError(f'illegal transition: {src} -> {dst}')
    return dst

def apply_batch(order_states, target, ctx=None):
    applied, skipped = [], []
    for order_no, src in order_states.items():
        try:
            move(src, target, ctx)
            applied.append(order_no)
        except ValueError as exc:
            skipped.append({'order_no': order_no, 'reason': str(exc)})
    return {'applied': applied, 'skipped': skipped}

def money(n):
    return round(n + 1e-9, 2)

def settle(order):
    base = order['goods'] + order['packing'] - order['discount']
    if base < 0:
        raise ValueError('优惠金额超过商品与包装金额')
    commission = money(base * order['commission_rate'])
    merchant = money(base - commission)
    platform = money(commission + order['delivery'] - order['rider_fee'])
    user_paid = money(order['goods'] + order['packing'] + order['delivery'] - order['discount'])
    return {'user_paid': user_paid, 'merchant': merchant,
            'rider': money(order['rider_fee']), 'platform': platform}

print(can_move('CREATED', 'PAID', {'paid': True}))
print(can_move('PAID', 'PAID'))
print(can_move('HUB_RECEIVED', 'DELIVERED'))
print(apply_batch({'A1001': 'HUB_RECEIVED', 'A1002': 'COOKED'}, 'SORTED'))
print(settle({'goods': 20, 'packing': 1, 'delivery': 3, 'discount': 2,
              'commission_rate': 0.08, 'rider_fee': 4}))