预算不多，校园外卖系统怎么做：先租SaaS再验订单异常

const 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: [],
  CLOSED: []
};

function canMove(from, to, ctx = {}) {
  if (!FLOW[from] || !FLOW[from].includes(to)) return false;
  if (to === 'PAID' && ctx.paid !== true) return false;
  return true;
}

function money(n) {
  return Number(n.toFixed(2));
}

function settle(order) {
  const base = order.goods + order.packing - order.discount;
  if (base < 0) throw new Error('优惠金额超过商品与包装金额');
  const commission = money(base * order.commissionRate);
  const merchant = money(base - commission);
  const platform = money(commission + order.delivery - order.riderFee);
  const userPaid = money(order.goods + order.packing + order.delivery - order.discount);
  return { userPaid, merchant, rider: money(order.riderFee), platform };
}

const transitions = [
  ['CREATED', 'PAID', { paid: true }],
  ['PAID', 'PAID', {}],
  ['HUB_RECEIVED', 'DELIVERED', {}],
  ['SORTED', 'DELIVERED', {}]
];

for (const [from, to, ctx] of transitions) {
  console.log(`${from}->${to}:`, canMove(from, to, ctx));
}

const normal = { goods: 20, packing: 1, delivery: 3, discount: 2, commissionRate: 0.08, riderFee: 4 };
console.log('normal:', settle(normal));

try {
  settle({ goods: 10, packing: 1, delivery: 3, discount: 30, commissionRate: 0.08, riderFee: 4 });
} catch (e) {
  console.log('abnormal:', e.message);
}