// /components/financialReports/financialReportService.js
'use strict';

const Class = require('../classes/classModel');
const Session = require('../sessions/sessionModel');
const Payment = require('../payments/paymentModel');
const Transaction = require('../payments/transactionModel');
const AppError = require('../../utils/AppError');
const { resolveDateRange, isWithinRange } = require('../../utils/financialRange');
const {
  getPayableAmount,
  isPaidTransaction,
  isActiveTransaction
} = require('../../utils/paymentAmount');
const {
  resolveSessionDurationHours,
  calculateSessionDurationHours,
  calculateBaseShare,
  calculateExtraExpenses,
  calculateProfessorPayout,
  calculateNetProfit,
  calculatePendingReceivables,
  calculateOverpaidAmount,
  calculateStudentRevenuePerSession
} = require('../../utils/professorShare');
const { sumExpensesInRange } = require('../expenses/expenseService');

const normalizeId = (value) => {
  if (value == null) return '';
  if (typeof value === 'object' && value._id != null) return String(value._id);
  return String(value);
};

/** Revenue collected/owed for a set of classIds, derived from Payment records (one payment ~ one class enrollment). */
const getRevenueByClass = async (classIds) => {
  const payments = await Payment.find({ classes: { $in: classIds }, isDeleted: { $ne: true } })
    .select('classes amount discount paidAmount')
    .lean();

  const byClass = new Map(classIds.map((id) => [String(id), { expectedRevenue: 0, actualReceivedRevenue: 0 }]));
  for (const payment of payments) {
    const payable = getPayableAmount(payment);
    const paid = Math.max(0, Number(payment.paidAmount) || 0);
    for (const classRef of payment.classes || []) {
      const key = String(classRef);
      if (!byClass.has(key)) continue;
      const entry = byClass.get(key);
      entry.expectedRevenue += payable;
      entry.actualReceivedRevenue += paid;
    }
  }
  return byClass;
};

const getSessionCountsByClass = async (classIds) => {
  const sessions = await Session.find({ class: { $in: classIds }, isDeleted: { $ne: true } }).select('class status').lean();
  const byClass = new Map(classIds.map((id) => [String(id), { total: 0, held: 0, scheduled: 0, cancelled: 0 }]));
  for (const session of sessions) {
    const key = String(session.class);
    if (!byClass.has(key)) continue;
    const entry = byClass.get(key);
    entry.total += 1;
    if (session.status === 'held') entry.held += 1;
    else if (session.status === 'cancelled') entry.cancelled += 1;
    else entry.scheduled += 1;
  }
  return byClass;
};

/**
 * Per-Class Report (Lifetime): aggregates all sessions, student payments (received vs.
 * pending), professor payout (share + expenses), and net class profit.
 */
const getClassReport = async (classId) => {
  const cls = await Class.findById(classId)
    .populate({ path: 'course', select: 'title hoursPerSection sectionCount' })
    .populate({ path: 'professor', select: 'name surname' })
    .lean();
  if (!cls) throw new AppError('CLASS_NOT_FOUND');

  const [revenueByClass, sessionCountsByClass] = await Promise.all([
    getRevenueByClass([cls._id]),
    getSessionCountsByClass([cls._id])
  ]);

  const revenue = revenueByClass.get(String(cls._id)) || { expectedRevenue: 0, actualReceivedRevenue: 0 };
  const sessionCounts = sessionCountsByClass.get(String(cls._id)) || { total: 0, held: 0, scheduled: 0, cancelled: 0 };

  const sessionDurationHours = resolveSessionDurationHours(cls);
  const payout = calculateProfessorPayout({
    payoutType: cls.payoutType,
    payoutPercentage: cls.payoutPercentage,
    payoutHourlyRate: cls.payoutHourlyRate,
    revenue: revenue.actualReceivedRevenue,
    sessionDurationHours,
    sessionsCount: sessionCounts.held,
    extraExpensePerSession: cls.extraExpensePerSession
  });

  const netProfit = calculateNetProfit({
    totalIncome: revenue.actualReceivedRevenue,
    professorTotalPayout: payout.totalPayout
  });

  return {
    class: {
      _id: cls._id,
      name: cls.name,
      course: cls.course,
      professor: cls.professor,
      numberOfSessions: cls.numberOfSessions,
      studentsCount: (cls.students || []).length,
      payoutType: cls.payoutType,
      payoutPercentage: cls.payoutPercentage,
      payoutHourlyRate: cls.payoutHourlyRate,
      extraExpensePerSession: cls.extraExpensePerSession,
      sessionDurationHours
    },
    sessions: {
      planned: cls.numberOfSessions ?? sessionCounts.total,
      held: sessionCounts.held,
      scheduled: sessionCounts.scheduled,
      cancelled: sessionCounts.cancelled
    },
    revenue: {
      expectedRevenue: revenue.expectedRevenue,
      actualReceivedRevenue: revenue.actualReceivedRevenue,
      pendingReceivables: calculatePendingReceivables(revenue.expectedRevenue, revenue.actualReceivedRevenue),
      overpaidAmount: calculateOverpaidAmount(revenue.expectedRevenue, revenue.actualReceivedRevenue)
    },
    professorPayout: payout,
    netProfit
  };
};

/**
 * Per-Session Report: evaluates one specific session — student revenue attributable to
 * this session, the professor's session-level share/expenses, and the session net margin.
 */
const getSessionReport = async (sessionId) => {
  const session = await Session.findById(sessionId)
    .populate({
      path: 'class',
      populate: [
        { path: 'course', select: 'title hoursPerSection sectionCount' },
        { path: 'professor', select: 'name surname' }
      ]
    })
    .lean();
  if (!session) throw new AppError('SESSION_NOT_FOUND');

  const cls = session.class;
  if (!cls) throw new AppError('CLASS_NOT_FOUND');

  const studentsCount = (cls.students || []).length;
  const plannedSessions = cls.numberOfSessions || (await Session.countDocuments({ class: cls._id }));

  const revenueByClass = await getRevenueByClass([cls._id]);
  const revenue = revenueByClass.get(String(cls._id)) || { expectedRevenue: 0, actualReceivedRevenue: 0 };

  // Prefer real payment data (handles per-student discounts); fall back to the class tuition when no payments exist yet.
  const finalTuitionFee = cls.hasDiscount ? Math.max(0, (cls.tuitionFee || 0) - (cls.discount || 0)) : (cls.tuitionFee || 0);
  const assignedTuitionPerStudent = studentsCount > 0 && revenue.expectedRevenue > 0
    ? revenue.expectedRevenue / studentsCount
    : finalTuitionFee;

  const studentRevenuePerSession = calculateStudentRevenuePerSession(assignedTuitionPerStudent, plannedSessions);
  const sessionIncome = studentRevenuePerSession * studentsCount;

  const sessionDurationHours = calculateSessionDurationHours(session.startTime, session.endTime)
    || resolveSessionDurationHours(cls);

  const sessionShare = calculateBaseShare({
    payoutType: cls.payoutType,
    payoutPercentage: cls.payoutPercentage,
    revenue: sessionIncome,
    payoutHourlyRate: cls.payoutHourlyRate,
    sessionDurationHours,
    sessionsCount: 1
  });
  const sessionExtraExpense = calculateExtraExpenses({
    extraExpensePerSession: cls.extraExpensePerSession,
    sessionsCount: 1
  });

  const sessionNetMargin = calculateNetProfit({
    totalIncome: sessionIncome,
    professorTotalPayout: sessionShare + sessionExtraExpense
  });

  return {
    session: {
      _id: session._id,
      topic: session.topic,
      day: session.day,
      startTime: session.startTime,
      endTime: session.endTime,
      status: session.status
    },
    class: {
      _id: cls._id,
      name: cls.name,
      course: cls.course,
      professor: cls.professor,
      studentsCount,
      plannedSessions
    },
    financials: {
      studentRevenuePerSession,
      sessionIncome,
      sessionDurationHours,
      professorSessionShare: sessionShare,
      sessionExtraExpense,
      sessionTotalPayout: sessionShare + sessionExtraExpense,
      sessionNetMargin
    }
  };
};

/**
 * Date-Range / Monthly Report: sessions held across all active classes within [start, end],
 * combined with general institutional expenses recorded in that same window.
 */
const getRangeReport = async (query = {}) => {
  const { start, end } = resolveDateRange(query);

  const classFilter = { isActive: { $ne: false }, isDeleted: { $ne: true } };
  if (query.classId) classFilter._id = query.classId;

  const classes = await Class.find(classFilter)
    .populate({ path: 'course', select: 'title hoursPerSection' })
    .populate({ path: 'professor', select: 'name surname' })
    .lean();
  const classIds = classes.map((c) => c._id);

  if (!classIds.length) {
    const generalExpenses = await sumExpensesInRange(start, end);
    return {
      range: { start, end },
      classes: [],
      totals: {
        totalReceived: 0,
        totalOutstanding: 0,
        totalProfessorPayouts: 0,
        generalExpenses,
        netProfit: -generalExpenses
      }
    };
  }

  const sessions = await Session.find({ class: { $in: classIds }, day: { $gte: start, $lte: end }, isDeleted: { $ne: true } })
    .select('class status day')
    .lean();

  const heldByClass = new Map();
  for (const session of sessions) {
    if (session.status !== 'held') continue;
    const key = String(session.class);
    heldByClass.set(key, (heldByClass.get(key) || 0) + 1);
  }

  const payments = await Payment.find({ classes: { $in: classIds }, isDeleted: { $ne: true } }).select('_id classes').lean();
  const paymentClassByPaymentId = new Map();
  const paymentIds = [];
  for (const payment of payments) {
    paymentIds.push(payment._id);
    const matchedClassId = (payment.classes || []).map(normalizeId).find((id) => classIds.some((c) => String(c) === id));
    paymentClassByPaymentId.set(String(payment._id), matchedClassId);
  }

  const transactions = paymentIds.length
    ? await Transaction.find({ payment: { $in: paymentIds } }).select('payment amount status date dueDate').lean()
    : [];

  const receivedByClass = new Map();
  const outstandingByClass = new Map();
  for (const trx of transactions) {
    const classKey = paymentClassByPaymentId.get(String(trx.payment));
    if (!classKey) continue;

    if (isPaidTransaction(trx) && isWithinRange(trx.date, start, end)) {
      receivedByClass.set(classKey, (receivedByClass.get(classKey) || 0) + (Number(trx.amount) || 0));
    } else if (isActiveTransaction(trx) && !isPaidTransaction(trx) && isWithinRange(trx.dueDate, start, end)) {
      outstandingByClass.set(classKey, (outstandingByClass.get(classKey) || 0) + (Number(trx.amount) || 0));
    }
  }

  const classRows = classes.map((cls) => {
    const key = String(cls._id);
    const sessionsHeldInRange = heldByClass.get(key) || 0;
    const receivedInRange = receivedByClass.get(key) || 0;
    const outstandingInRange = outstandingByClass.get(key) || 0;
    const sessionDurationHours = resolveSessionDurationHours(cls);

    const payout = calculateProfessorPayout({
      payoutType: cls.payoutType,
      payoutPercentage: cls.payoutPercentage,
      payoutHourlyRate: cls.payoutHourlyRate,
      revenue: receivedInRange,
      sessionDurationHours,
      sessionsCount: sessionsHeldInRange,
      extraExpensePerSession: cls.extraExpensePerSession
    });

    return {
      class: {
        _id: cls._id,
        name: cls.name,
        course: cls.course,
        professor: cls.professor
      },
      sessionsHeldInRange,
      receivedInRange,
      outstandingInRange,
      professorPayout: payout
    };
  });

  const generalExpenses = await sumExpensesInRange(start, end);
  const totalReceived = classRows.reduce((sum, row) => sum + row.receivedInRange, 0);
  const totalOutstanding = classRows.reduce((sum, row) => sum + row.outstandingInRange, 0);
  const totalProfessorPayouts = classRows.reduce((sum, row) => sum + row.professorPayout.totalPayout, 0);
  const netProfit = totalReceived - totalProfessorPayouts - generalExpenses;

  return {
    range: { start, end },
    classes: classRows,
    totals: {
      totalReceived,
      totalOutstanding,
      totalProfessorPayouts,
      generalExpenses,
      netProfit
    }
  };
};

module.exports = {
  getClassReport,
  getSessionReport,
  getRangeReport
};