// /components/sessions/sessionService.js

const Session = require('./sessionModel');
const Course = require('../courses/courseModel');
const Class = require('../classes/classModel');
const Professor = require('../professors/professorModel');
const AppError = require('../../utils/AppError');
const eventEmitter = require('../../events/eventEmitter');
const EVENT_NAMES = require('../../constants/eventNames');
const { parsePaginationAndSort, buildFilterQuery, calculateMeta } = require('../../utils/pagination');

const STATUS_MAP = {
  scheduled: 'scheduled',
  held: 'held',
  cancelled: 'cancelled',
  Scheduled: 'scheduled',
  Held: 'held',
  Cancelled: 'cancelled',
  canceled: 'cancelled',
  Canceled: 'cancelled'
};

const normalizeSessionPayload = (data) => {
  const payload = { ...data };

  if (payload.date && !payload.day) {
    payload.day = payload.date;
  }
  delete payload.date;

  if (payload.status) {
    payload.status = STATUS_MAP[payload.status] || payload.status;
  }

  return payload;
};

const createSession = async (data, actorId = null) => {
  // Support bulk create from dashboard: { sessions: [...], courseId, professorId, classId }
  if (Array.isArray(data.sessions)) {
    const created = [];
    for (const item of data.sessions) {
      const session = await createSession({
        ...item,
        course: item.course || data.courseId || data.course,
        class: item.class || data.classId || data.class,
        professor: item.professor || data.professorId || data.professor
      }, actorId);
      created.push(session);
    }
    return created;
  }

  const payload = normalizeSessionPayload(data);

  if (!payload.day) {
    throw new AppError('VALIDATION_FAILED', { day: 'Date is required' }, 'تاریخ جلسه الزامی است.');
  }
  if (!payload.startTime || !payload.endTime) {
    throw new AppError('VALIDATION_FAILED', { time: 'Start and end time are required' }, 'ساعت شروع و پایان الزامی است.');
  }

  const course = await Course.findById(payload.course);
  if (!course) throw new AppError('COURSE_NOT_FOUND');

  const classItem = await Class.findById(payload.class);
  if (!classItem) throw new AppError('NOT_FOUND', null, 'کلاس یافت نشد.');

  const professor = await Professor.findById(payload.professor);
  if (!professor) throw new AppError('PROFESSOR_NOT_FOUND');

  const session = await Session.create(payload);
  eventEmitter.emit(EVENT_NAMES.SESSION_CREATED, {
    sessionId: session._id,
    courseId: session.course,
    classId: session.class,
    actorId
  });
  return session;
};

const getSessionById = async (id) => {
  const session = await Session.findById(id)
    .populate('course', 'title type')
    .populate({
      path: 'class',
      select: 'name students capacity',
      populate: { path: 'students', select: 'name nationalIdCode phoneNumber gender' }
    })
    .populate('professor', 'name surname email phoneNumber')
    .populate('attendanceList.user', 'name username nationalIdCode');
  if (!session) {
    throw new AppError('SESSION_NOT_FOUND');
  }
  return session;
};

const startOfToday = () => {
  const d = new Date();
  d.setHours(0, 0, 0, 0);
  return d;
};

/** Upcoming soonest first, then most recent past — nearest attendance date. */
const sortByClosestAttendance = (sessions) => {
  const today = startOfToday().getTime();
  return [...sessions].sort((a, b) => {
    const da = new Date(a.day || a.date || 0).getTime();
    const db = new Date(b.day || b.date || 0).getTime();
    const aUpcoming = da >= today;
    const bUpcoming = db >= today;
    if (aUpcoming && bUpcoming) return da - db;
    if (!aUpcoming && !bUpcoming) return db - da;
    return aUpcoming ? -1 : 1;
  });
};

const populateSessionList = (query) =>
  query
    .populate('course', 'title type')
    .populate('class', 'name')
    .populate('professor', 'name surname');

const getAllSessions = async (queryParams) => {
  const { page, limit, skip } = parsePaginationAndSort(queryParams, 'day', 'asc');
  const filter = buildFilterQuery(queryParams, ['topic', 'place', 'note'], [
    'page',
    'limit',
    'sortBy',
    'sortOrder',
    'q',
    'lang',
    'courseId',
    'classId',
    'professorId',
    'class' // handled below so we always cast consistently
  ]);

  if (queryParams.courseId) filter.course = queryParams.courseId;
  const classFilter = queryParams.classId || queryParams.class;
  if (classFilter) {
    filter.class = classFilter;
  }
  if (queryParams.professorId) filter.professor = queryParams.professorId;

  if (filter.status) {
    filter.status = STATUS_MAP[filter.status] || filter.status;
  }

  const [matched, totalCount] = await Promise.all([
    populateSessionList(Session.find(filter)).lean(),
    Session.countDocuments(filter)
  ]);

  const sessions = sortByClosestAttendance(matched).slice(skip, skip + limit);
  const meta = calculateMeta(totalCount, page, limit);
  return { data: sessions, meta };
};

const updateSession = async (id, updateData, actorId = null) => {
  const session = await Session.findById(id);
  if (!session) {
    throw new AppError('SESSION_NOT_FOUND');
  }

  const payload = normalizeSessionPayload(updateData);

  if (payload.day === null || payload.day === '') {
    throw new AppError('VALIDATION_FAILED', { day: 'Date is required' }, 'تاریخ جلسه الزامی است.');
  }

  if (payload.status === 'cancelled' && session.status !== 'cancelled') {
    eventEmitter.emit(EVENT_NAMES.SESSION_CANCELLED, {
      sessionId: session._id,
      courseId: session.course,
      topic: payload.topic || session.topic,
      actorId
    });
  }

  Object.assign(session, payload);
  await session.save();
  return getSessionById(session._id);
};

const deleteSession = async (id) => {
  const session = await Session.findById(id);
  if (!session) {
    throw new AppError('SESSION_NOT_FOUND');
  }
  await Session.findByIdAndDelete(id);
  return null;
};

const normalizeIds = (ids) => {
  if (!Array.isArray(ids)) return [];
  return [...new Set(ids.map((id) => String(id || '').trim()).filter(Boolean))];
};

const bulkDeleteSessions = async (ids) => {
  const sessionIds = normalizeIds(ids);
  if (!sessionIds.length) {
    throw new AppError('VALIDATION_FAILED', { ids: 'Required' }, 'هیچ جلسه‌ای انتخاب نشده است.');
  }

  const result = await Session.deleteMany({ _id: { $in: sessionIds } });
  return { deletedCount: result.deletedCount || 0 };
};

const bulkUpdateSessionStatus = async (ids, status, actorId = null) => {
  const sessionIds = normalizeIds(ids);
  if (!sessionIds.length) {
    throw new AppError('VALIDATION_FAILED', { ids: 'Required' }, 'هیچ جلسه‌ای انتخاب نشده است.');
  }

  const normalizedStatus = STATUS_MAP[status] || status;
  if (!['scheduled', 'held', 'cancelled'].includes(normalizedStatus)) {
    throw new AppError('VALIDATION_FAILED', { status: 'Invalid' }, 'وضعیت جلسه نامعتبر است.');
  }

  const sessions = await Session.find({ _id: { $in: sessionIds } });
  let updatedCount = 0;

  for (const session of sessions) {
    const previousStatus = session.status;
    session.status = normalizedStatus;
    await session.save();
    updatedCount += 1;

    if (normalizedStatus === 'cancelled' && previousStatus !== 'cancelled') {
      eventEmitter.emit(EVENT_NAMES.SESSION_CANCELLED, {
        sessionId: session._id,
        courseId: session.course,
        classId: session.class,
        actorId
      });
    }
  }

  return { updatedCount, status: normalizedStatus };
};

const searchSessions = async (queryParams) => {
  return getAllSessions(queryParams);
};

const updateSessionAttendance = async (sessionId, attendanceList, recordedBy = null) => {
  const session = await Session.findById(sessionId);
  if (!session) throw new AppError('SESSION_NOT_FOUND');

  const list = Array.isArray(attendanceList) ? attendanceList : [];

  session.attendanceList = list.map((record) => ({
    user: record.user || record.userId,
    status: record.status || 'present',
    note: record.note || '',
    recordedBy
  }));

  await session.save();

  eventEmitter.emit(EVENT_NAMES.ATTENDANCE_RECORDED, {
    sessionId: session._id,
    recordCount: list.length,
    recordedBy
  });

  return getSessionById(sessionId);
};

const getMySessions = async (userId, queryParams) => {
  const userClasses = await Class.find({ students: userId }).select('_id');
  const classIds = userClasses.map((c) => c._id);

  const filter = { class: { $in: classIds } };

  const { page, limit, skip } = parsePaginationAndSort(queryParams, 'day', 'asc');
  const [matched, totalCount] = await Promise.all([
    populateSessionList(Session.find(filter)).lean(),
    Session.countDocuments(filter)
  ]);

  const sessions = sortByClosestAttendance(matched).slice(skip, skip + limit);
  const meta = calculateMeta(totalCount, page, limit);
  return { data: sessions, meta };
};

module.exports = {
  createSession,
  getSessionById,
  getAllSessions,
  updateSession,
  deleteSession,
  bulkDeleteSessions,
  bulkUpdateSessionStatus,
  searchSessions,
  updateSessionAttendance,
  getMySessions
};