const { Op } = require('sequelize');
const { Bill } = require('../models');

const generateBillNo = () => {
  const date = new Date();
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, '0');
  const day = String(date.getDate()).padStart(2, '0');
  const ms = String(date.getTime()).slice(-6);
  const random = Math.floor(Math.random() * 1000).toString().padStart(3, '0');
  return `B${year}${month}${day}${ms}${random}`;
};

const toNumber = (value) => {
  const parsed = parseFloat(value);
  return Number.isFinite(parsed) ? parsed : 0;
};

const billMonthOf = (date) => {
  if (!date) return null;
  if (typeof date === 'string') return date.substring(0, 7);
  return new Date(date).toISOString().substring(0, 7);
};

const createRentalBill = async ({
  rentalId,
  roomId,
  renterId,
  type = 'income',
  category,
  amount,
  billDate,
  billMonth,
  settlementType = 'normal',
  sourceEventId = null,
  sourceType = null,
  sourceId = null,
  remark,
  tenantId,
  createBy,
  transaction
}) => {
  const receivableAmount = toNumber(amount);
  if (receivableAmount <= 0) return null;

  return Bill.create({
    billNo: generateBillNo(),
    rentalId,
    roomId,
    renterId,
    type,
    category,
    receivableAmount,
    receivedAmount: 0,
    status: 'unpaid',
    billDate: billDate || new Date(),
    billMonth: billMonth || billMonthOf(billDate),
    settlementType,
    sourceEventId,
    sourceType,
    sourceId,
    remark,
    tenantId,
    createBy,
    updateBy: createBy
  }, { transaction });
};

const createInitialBills = async ({ rental, renterName = '', settlementType = 'normal', sourceEventId = null, transaction }) => {
  const bills = [];
  const label = settlementType === 'renew' ? '续租' : settlementType === 'change_room' ? '换房' : '租约';
  const operatorId = rental.createBy || rental.updateBy;

  const rentBill = await createRentalBill({
    rentalId: rental.id,
    roomId: rental.roomId,
    renterId: rental.renterId,
    category: 'rent',
    amount: rental.rent,
    billDate: rental.startDate,
    settlementType,
    sourceEventId,
    remark: `${label}首期租金 - ${renterName}`,
    tenantId: rental.tenantId,
    createBy: operatorId,
    transaction
  });
  if (rentBill) bills.push(rentBill);

  const depositBill = await createRentalBill({
    rentalId: rental.id,
    roomId: rental.roomId,
    renterId: rental.renterId,
    category: 'deposit',
    amount: rental.deposit,
    billDate: rental.startDate,
    settlementType,
    sourceEventId,
    remark: `${label}押金 - ${renterName}`,
    tenantId: rental.tenantId,
    createBy: operatorId,
    transaction
  });
  if (depositBill) bills.push(depositBill);

  return bills;
};

const createDepositDiffBill = async ({ rental, oldDeposit, newDeposit, renterName = '', settlementType, transaction }) => {
  const diff = toNumber(newDeposit) - toNumber(oldDeposit);
  if (diff === 0) return null;

  return createRentalBill({
    rentalId: rental.id,
    roomId: rental.roomId,
    renterId: rental.renterId,
    type: diff > 0 ? 'income' : 'expense',
    category: 'deposit',
    amount: Math.abs(diff),
    billDate: rental.startDate,
    settlementType,
    sourceEventId: rental.prevRentalId || null,
    remark: diff > 0 ? `补交押金 - ${renterName}` : `退还押金差额 - ${renterName}`,
    tenantId: rental.tenantId,
    createBy: rental.createBy || rental.updateBy,
    transaction
  });
};

const syncEditableInitialBills = async ({ rental, oldRental, renterName = '', operatorId, transaction }) => {
  const activeInitialBills = await Bill.findAll({
    where: {
      rentalId: rental.id,
      tenantId: rental.tenantId,
      settlementType: 'normal',
      category: { [Op.in]: ['rent', 'deposit'] },
      status: 'unpaid',
      isDeleted: 0
    },
    transaction
  });

  for (const bill of activeInitialBills) {
    if (bill.category === 'rent') {
      await bill.update({
        roomId: rental.roomId,
        renterId: rental.renterId,
        receivableAmount: rental.rent,
        billDate: rental.startDate,
        billMonth: billMonthOf(rental.startDate),
        remark: `租约首期租金 - ${renterName}`,
        updateBy: operatorId
      }, { transaction });
    }

    if (bill.category === 'deposit') {
      const deposit = toNumber(rental.deposit);
      if (deposit > 0) {
        await bill.update({
          roomId: rental.roomId,
          renterId: rental.renterId,
          receivableAmount: deposit,
          billDate: rental.startDate,
          billMonth: billMonthOf(rental.startDate),
          remark: `租约押金 - ${renterName}`,
          updateBy: operatorId
        }, { transaction });
      } else {
        await bill.update({ status: 'cancelled', isDeleted: 1, updateBy: operatorId }, { transaction });
      }
    }
  }

  const hasDepositBill = activeInitialBills.some(bill => bill.category === 'deposit');
  if (!hasDepositBill && toNumber(oldRental.deposit) <= 0 && toNumber(rental.deposit) > 0) {
    await createRentalBill({
      rentalId: rental.id,
      roomId: rental.roomId,
      renterId: rental.renterId,
      category: 'deposit',
      amount: rental.deposit,
      billDate: rental.startDate,
      settlementType: 'normal',
      remark: `租约押金 - ${renterName}`,
      tenantId: rental.tenantId,
      createBy: operatorId,
      transaction
    });
  }
};

const cancelUnpaidBillsForRental = async ({ rentalId, tenantId, operatorId, transaction }) => {
  return Bill.update(
    { status: 'cancelled', isDeleted: 1, updateBy: operatorId },
    {
      where: {
        rentalId,
        tenantId,
        status: 'unpaid',
        isDeleted: 0
      },
      transaction
    }
  );
};

const assertRentalCanBeDeleted = async ({ rentalId, tenantId, transaction }) => {
  const bills = await Bill.findAll({
    where: {
      rentalId,
      tenantId,
      status: { [Op.ne]: 'cancelled' },
      isDeleted: 0
    },
    attributes: ['id', 'status', 'category', 'receivedAmount'],
    transaction
  });

  if (bills.length === 0) return;

  const paidLike = bills.filter(bill => ['paid', 'partial'].includes(bill.status) || toNumber(bill.receivedAmount) > 0);
  if (paidLike.length === 0) return;

  const error = new Error(
    paidLike.length > 0
      ? '该租约已有收款记录，不能删除。请办理退租或作废未收账单，并保留历史流水。'
      : `该租约下有 ${bills.length} 笔有效未收账单，请先作废账单或办理退租后再删除。`
  );
  error.statusCode = 400;
  throw error;
};

const validatePaymentAmount = (bill, amount) => {
  if (bill.status === 'paid') {
    const error = new Error('该账单已收清，无法继续收款');
    error.statusCode = 400;
    throw error;
  }
  if (bill.status === 'cancelled') {
    const error = new Error('该账单已取消，无法收款');
    error.statusCode = 400;
    throw error;
  }

  const receivableAmount = toNumber(bill.receivableAmount);
  const currentReceived = toNumber(bill.receivedAmount);
  const paymentAmount = toNumber(amount);
  const remainingAmount = receivableAmount - currentReceived;

  if (paymentAmount <= 0) {
    const error = new Error('支付金额必须大于0');
    error.statusCode = 400;
    throw error;
  }
  if (paymentAmount > remainingAmount) {
    const error = new Error(`支付金额不能超过剩余应收金额 ¥${remainingAmount.toFixed(2)}`);
    error.statusCode = 400;
    throw error;
  }

  const newReceivedAmount = currentReceived + paymentAmount;
  return {
    paymentAmount,
    newReceivedAmount,
    newStatus: newReceivedAmount >= receivableAmount ? 'paid' : 'partial'
  };
};

module.exports = {
  generateBillNo,
  billMonthOf,
  createRentalBill,
  createInitialBills,
  createDepositDiffBill,
  syncEditableInitialBills,
  cancelUnpaidBillsForRental,
  assertRentalCanBeDeleted,
  validatePaymentAmount
};