// /components/dashboard/dashboardService.js
'use strict';

const User = require('../users/userModel');
const Professor = require('../professors/professorModel');
const Course = require('../courses/courseModel');
const Session = require('../sessions/sessionModel');

/**
 * Returns aggregated statistics for the admin dashboard
 */
const getAdminStats = async () => {
  const [
    totalUsers,
    activeUsers,
    totalProfessors,
    activeProfessors,
    totalCourses,
    totalSessions,
    recentSessions
  ] = await Promise.all([
    User.countDocuments({}),
    User.countDocuments({ isActive: true }),
    Professor.countDocuments({}),
    Professor.countDocuments({ isActive: true }),
    Course.countDocuments({}),
    Session.countDocuments({}),
    Session.find({})
      .sort({ day: -1 })
      .limit(8)
      .populate('course', 'title type')
      .populate('class', 'name')
      .populate('professor', 'name surname')
      .lean()
  ]);

  // Daily enrollment trend (last 14 days via User.createdAt)
  const daysBack = 13;
  const rangeStart = new Date();
  rangeStart.setHours(0, 0, 0, 0);
  rangeStart.setDate(rangeStart.getDate() - daysBack);

  const dailyUsersRaw = await User.aggregate([
    { $match: { createdAt: { $gte: rangeStart } } },
    {
      $group: {
        _id: {
          year: { $year: '$createdAt' },
          month: { $month: '$createdAt' },
          day: { $dayOfMonth: '$createdAt' }
        },
        count: { $sum: 1 }
      }
    },
    { $sort: { '_id.year': 1, '_id.month': 1, '_id.day': 1 } }
  ]);

  // Fill every day in the range so the chart stays continuous
  const dailyUsers = [];
  for (let i = 0; i <= daysBack; i += 1) {
    const date = new Date(rangeStart);
    date.setDate(rangeStart.getDate() + i);
    const year = date.getFullYear();
    const month = date.getMonth() + 1;
    const day = date.getDate();
    const match = dailyUsersRaw.find(
      (item) => item._id.year === year && item._id.month === month && item._id.day === day
    );
    dailyUsers.push({
      _id: { year, month, day },
      date: date.toISOString(),
      count: match ? match.count : 0
    });
  }

  // Daily sessions trend (same window)
  const dailySessionsRaw = await Session.aggregate([
    { $match: { createdAt: { $gte: rangeStart } } },
    {
      $group: {
        _id: {
          year: { $year: '$createdAt' },
          month: { $month: '$createdAt' },
          day: { $dayOfMonth: '$createdAt' }
        },
        count: { $sum: 1 }
      }
    },
    { $sort: { '_id.year': 1, '_id.month': 1, '_id.day': 1 } }
  ]);

  const dailySessions = dailyUsers.map((day) => {
    const match = dailySessionsRaw.find(
      (item) =>
        item._id.year === day._id.year &&
        item._id.month === day._id.month &&
        item._id.day === day._id.day
    );
    return {
      _id: day._id,
      date: day.date,
      count: match ? match.count : 0
    };
  });

  return {
    totals: {
      users: totalUsers,
      activeUsers,
      professors: totalProfessors,
      activeProfessors,
      courses: totalCourses,
      sessions: totalSessions
    },
    recentSessions,
    charts: {
      dailyUsers,
      dailySessions
    }
  };
};

module.exports = { getAdminStats };