// /components/payments/paymentService.js
'use strict';

const Payment = require('./paymentModel');
const Transaction = require('./transactionModel');
const AppError = require('../../utils/AppError');
const eventEmitter = require('../../events/eventEmitter');
const EVENT_NAMES = require('../../constants/eventNames');
const { calculateMeta, escapeRegex, getSearchTerm } = require('../../utils/pagination');
const User = require('../users/userModel');
const Course = require('../courses/courseModel');
const Class = require('../classes/classModel');
const Session = require('../sessions/sessionModel');
const { sendInvoiceCreatedSms } = require('../../utils/senders/smsMessages');
const { buildClassScheduleContext } = require('../../utils/classSchedule');
const { parseImportDate } = require('../../utils/jalaliDate');
const { pickNotifyFlags, omitNotifyFields } = require('../../utils/notifyFlags');
const {
  getPayableAmount,
  normalizeDiscount,
  sanitizeNotes,
  isPaidTransaction,
  sumPaidTransactions
} = require('../../utils/paymentAmount');
const logger = require('../../utils/logger');

const PAYMENT_METHODS = new Set(['online', 'card', 'cash']);

const populatePayment = (query) => query
  .populate({ path: 'user', select: 'name phoneNumber' })
  .populate({ path: 'classes', select: 'name tuitionFee' })
  .populate({ path: 'course', select: 'title price' })
  .populate({ path: 'transactions', options: { sort: { dueDate: 1, date: 1, createdAt: 1 } } });

const attachTransactions = async (payments) => {
  const list = Array.isArray(payments) ? payments : [payments];
  const ids = list.map((item) => item._id).filter(Boolean);
  if (!ids.length) return payments;

  const transactions = await Transaction.find({ payment: { $in: ids } })
    .sort({ dueDate: 1, date: 1, createdAt: 1 })
    .lean();
  const byPayment = new Map();
  for (const trx of transactions) {
    const key = String(trx.payment);
    if (!byPayment.has(key)) byPayment.set(key, []);
    byPayment.get(key).push(trx);
  }
  for (const payment of list) {
    payment.transactions = byPayment.get(String(payment._id)) || [];
  }
  return payments;
};

const refreshPaymentTotals = async (payment) => {
  const transactions = await Transaction.find({ payment: payment._id }).lean();
  payment.paidAmount = sumPaidTransactions(transactions);
  const pending = transactions
    .filter((trx) => !isPaidTransaction(trx))
    .sort((a, b) => new Date(a.dueDate || 0) - new Date(b.dueDate || 0));
  payment.dueDate = pending[0]?.dueDate || payment.dueDate;
  await payment.save();
  return payment;
};

const emitPaymentStatusChangedIfNeeded = (payment, previousStatus, actorId = null) => {
  if (payment.status === previousStatus) return;
  eventEmitter.emit(EVENT_NAMES.PAYMENT_STATUS_CHANGED, {
    paymentId: payment._id,
    userId: payment.user,
    oldStatus: previousStatus,
    newStatus: payment.status,
    actorId
  });
};

const reconcilePendingTransactions = async (payment, { adjustAmount = true } = {}) => {
  const transactions = await Transaction.find({ payment: payment._id }).lean();
  const remaining = getPayableAmount(payment) - sumPaidTransactions(transactions);
  const pending = await Transaction.find({ payment: payment._id, status: 'pending' }).sort({ dueDate: 1 });

  if (remaining <= 0) {
    await Transaction.deleteMany({ payment: payment._id, status: 'pending' });
    return;
  }

  if (pending.length) {
    if (adjustAmount) {
      const pendingTotal = pending.reduce((sum, row) => sum + row.amount, 0);
      if (pendingTotal !== remaining) {
        pending[0].amount = remaining;
        await pending[0].save();
      }
    }
    if (pending.length > 1) {
      await Transaction.deleteMany({ _id: { $in: pending.slice(1).map((row) => row._id) } });
    }
    return;
  }

  await Transaction.create(buildTransactionPayload(payment, {
    amount: remaining,
    status: 'pending',
    dueDate: payment.dueDate || new Date()
  }));
};

const buildTransactionPayload = (payment, trxData, actorId = null) => {
  const status = trxData.status === 'pending' ? 'pending' : (trxData.status === 'paid' || trxData.date ? 'paid' : 'pending');
  const paidDate = parseDate(trxData.date) || (status === 'paid' ? new Date() : undefined);
  const dueDate = parseDate(trxData.dueDate) || paidDate || parseDate(payment.dueDate) || new Date();
  const payload = {
    payment: payment._id,
    user: payment.user,
    amount: Number(trxData.amount) || 0,
    receiptNumber: trxData.receiptNumber != null && trxData.receiptNumber !== ''
      ? String(trxData.receiptNumber)
      : '',
    notes: sanitizeNotes(trxData.notes),
    recordedBy: actorId || trxData.recordedBy,
    date: status === 'paid' ? paidDate : undefined,
    dueDate,
    status
  };
  if (PAYMENT_METHODS.has(trxData.method)) payload.method = trxData.method;
  else if (status === 'paid') payload.method = 'card';
  return payload;
};

const parseDate = (value) => {
  if (!value) return null;
  if (value instanceof Date) {
    return Number.isNaN(value.getTime()) ? null : value;
  }
  const parsed = parseImportDate(value);
  return parsed && !Number.isNaN(parsed.getTime()) ? parsed : null;
};

const createTransactionsForPayment = async (payment, transactions, actorId = null) => {
  const rows = Array.isArray(transactions) ? transactions : [];
  const created = [];
  for (const trx of rows) {
    const payload = buildTransactionPayload(payment, trx, actorId);
    if (!payload.amount) continue;
    created.push(await Transaction.create(payload));
  }
  return created;
};

const getAllPayments = async (query) => {
  const page = parseInt(query.page) || 1;
  const limit = Math.min(parseInt(query.limit) || 20, 200);
  const skip = (page - 1) * limit;

  const filter = {};
  if (query.userId) filter.user = query.userId;
  if (query.status) filter.status = query.status;

  const searchTerm = getSearchTerm(query);
  if (searchTerm) {
    const searchRegex = new RegExp(escapeRegex(searchTerm), 'i');
    const matchedUsers = await User.find({
      $or: [
        { name: searchRegex },
        { phoneNumber: searchRegex },
        { nationalIdCode: searchRegex }
      ]
    }).select('_id').lean();

    filter.$or = [
      { notes: searchRegex },
      { status: searchRegex },
      { user: { $in: matchedUsers.map((u) => u._id) } }
    ];
  }

  const [items, total] = await Promise.all([
    Payment.find(filter)
      .populate({ path: 'user', select: 'name' })
      .populate({ path: 'classes', select: 'name' })
      .populate({ path: 'course', select: 'title' })
      .skip(skip).limit(limit).sort({ createdAt: -1 }).lean(),
    Payment.countDocuments(filter)
  ]);

  await attachTransactions(items);
  return { data: items, meta: calculateMeta(total, page, limit) };
};

const getPaymentById = async (id) => {
  const payment = await populatePayment(Payment.findById(id)).lean();
  if (!payment) throw new AppError('PAYMENT_NOT_FOUND');
  if (!Array.isArray(payment.transactions)) payment.transactions = [];
  return payment;
};

const createPayment = async (body, actorId = null) => {
  const notify = pickNotifyFlags(body);
  const payload = omitNotifyFields(body);
  const incomingTransactions = Array.isArray(payload.transactions) ? payload.transactions : null;
  delete payload.transactions;

  const payment = await Payment.create({
    ...payload,
    discount: normalizeDiscount(payload.discount, payload.amount),
    notes: sanitizeNotes(payload.notes),
    paidAmount: payload.paidAmount || 0
  });

  if (incomingTransactions?.length) {
    await createTransactionsForPayment(payment, incomingTransactions, actorId);
  } else if (payment.dueDate && getPayableAmount(payment) > 0) {
    await Transaction.create(buildTransactionPayload(payment, {
      amount: getPayableAmount(payment),
      status: 'pending',
      dueDate: payment.dueDate
    }, actorId));
  }

  await refreshPaymentTotals(payment);

  if (actorId) {
    eventEmitter.emit(EVENT_NAMES.PAYMENT_CREATED, {
      paymentId: payment._id,
      userId: payment.user,
      actorId
    });
  }

  if (notify.sms) {
    try {
      const user = await User.findById(payment.user).select('name phoneNumber').lean();
      if (user?.phoneNumber) {
        let courseName = '';
        let schedule = { classStartDate: '', classDays: '', courseTime: '' };
        if (payment.course) {
          const course = await Course.findById(payment.course).select('title').lean();
          if (course?.title) courseName = course.title;
        }
        if (payment.classes && payment.classes.length > 0) {
          const cls = await Class.findById(payment.classes[0]).populate('course', 'title').lean();
          if (!courseName) {
            if (cls?.course?.title) {
              courseName = cls.course.title;
            } else if (cls?.name) {
              courseName = cls.name;
            }
          }
          if (cls) {
            const sessions = await Session.find({ class: cls._id })
              .select('day startTime endTime')
              .sort({ day: 1 })
              .lean();
            schedule = buildClassScheduleContext(cls, sessions);
          }
        }

        await sendInvoiceCreatedSms(user.phoneNumber, {
          fullName: user.name || '',
          amount: getPayableAmount(payment),
          course: courseName || '-',
          ...schedule
        }, user._id);
      }
    } catch (err) {
      logger.error(`[createPayment] Invoice SMS failed for payment ${payment._id}: ${err.message}`);
    }
  }

  return getPaymentById(payment._id);
};

const updatePayment = async (id, body, actorId = null) => {
  const payment = await Payment.findById(id);
  if (!payment) throw new AppError('PAYMENT_NOT_FOUND');

  const previousStatus = payment.status;
  const incomingTransactions = Array.isArray(body.transactions) ? body.transactions : null;
  const payload = { ...body };
  delete payload.transactions;

  Object.assign(payment, payload);
  if (body.discount !== undefined) {
    payment.discount = normalizeDiscount(body.discount, payment.amount);
  }
  if (body.notes !== undefined) {
    payment.notes = sanitizeNotes(body.notes);
  }
  await payment.save();

  if (incomingTransactions) {
    await Transaction.deleteMany({ payment: payment._id });
    await createTransactionsForPayment(payment, incomingTransactions, actorId);
    await refreshPaymentTotals(payment);
  }

  emitPaymentStatusChangedIfNeeded(payment, previousStatus, actorId);

  return getPaymentById(payment._id);
};

const deletePayment = async (id) => {
  const payment = await Payment.findByIdAndDelete(id);
  if (!payment) throw new AppError('PAYMENT_NOT_FOUND');
  await Transaction.deleteMany({ payment: id });
  return null;
};

const searchPayments = async (query) => getAllPayments(query);

const addTransaction = async (paymentId, trxData, actorId = null) => {
  const payment = await Payment.findById(paymentId);
  if (!payment) throw new AppError('PAYMENT_NOT_FOUND');

  const previousStatus = payment.status;
  const payload = buildTransactionPayload(payment, { ...trxData, status: trxData.status || 'paid' }, actorId);
  if (!payload.amount) throw new AppError('VALIDATION_FAILED', { amount: 'Amount is required' }, 'مبلغ تراکنش الزامی است.');
  await Transaction.create(payload);

  await reconcilePendingTransactions(payment);
  await refreshPaymentTotals(payment);

  eventEmitter.emit(EVENT_NAMES.PAYMENT_TRANSACTION_ADDED, {
    paymentId: payment._id,
    userId: payment.user,
    actorId
  });
  emitPaymentStatusChangedIfNeeded(payment, previousStatus, actorId);

  return getPaymentById(paymentId);
};

const updateTransaction = async (transactionId, body, actorId = null) => {
  const trx = await Transaction.findById(transactionId);
  if (!trx) throw new AppError('TRANSACTION_NOT_FOUND');

  const payment = await Payment.findById(trx.payment);
  if (!payment) throw new AppError('PAYMENT_NOT_FOUND');

  const previousStatus = payment.status;
  const merged = {
    amount: body.amount !== undefined ? body.amount : trx.amount,
    status: body.status !== undefined ? body.status : trx.status,
    method: body.method !== undefined ? body.method : trx.method,
    receiptNumber: body.receiptNumber !== undefined ? body.receiptNumber : trx.receiptNumber,
    notes: body.notes !== undefined ? body.notes : trx.notes,
    dueDate: body.dueDate !== undefined ? body.dueDate : trx.dueDate,
    date: body.date !== undefined ? body.date : trx.date
  };

  const payload = buildTransactionPayload(payment, merged, actorId);
  trx.amount = payload.amount;
  trx.status = payload.status;
  trx.receiptNumber = payload.receiptNumber;
  trx.notes = payload.notes;
  trx.dueDate = payload.dueDate;
  if (payload.status === 'paid') {
    trx.method = payload.method;
    trx.date = payload.date;
  } else {
    trx.method = undefined;
    trx.date = undefined;
    trx.receiptNumber = '';
  }
  if (actorId) trx.recordedBy = actorId;

  await trx.save();
  // Preserve admin-edited amounts; only reconcile balance when recording new payments.
  await reconcilePendingTransactions(payment, { adjustAmount: false });
  await refreshPaymentTotals(payment);
  emitPaymentStatusChangedIfNeeded(payment, previousStatus, actorId);

  return getPaymentById(payment._id);
};

const getMyPayments = async (userId, query = {}) => {
  return getAllPayments({ ...query, userId });
};

module.exports = {
  getAllPayments,
  getPaymentById,
  createPayment,
  updatePayment,
  deletePayment,
  searchPayments,
  addTransaction,
  updateTransaction,
  getMyPayments,
  createTransactionsForPayment,
  refreshPaymentTotals,
  buildTransactionPayload,
  reconcilePendingTransactions,
  // Aliases for older call sites
  getAll: getAllPayments,
  getOne: getPaymentById,
  create: createPayment,
  recordTransaction: addTransaction,
  remove: deletePayment
};