// Timetable group and entry data access helpers.

const { fetchPagedRows, validateMaxLength } = require('./utils');

const NAME_MAX_LENGTH = 255;
const DESCRIPTION_MAX_LENGTH = 255;
const DEFAULT_TIME_ZONE = 'Europe/London';

function normalizeTimeZone(value, fallback) {
  const raw = String(value || '').trim();
  if (!raw) {
    return String(fallback || DEFAULT_TIME_ZONE).trim() || DEFAULT_TIME_ZONE;
  }

  try {
    new Intl.DateTimeFormat('en-GB', { timeZone: raw }).format(new Date());
    return raw;
  } catch (_error) {
    const error = new Error('Timetable time zone is invalid.');
    error.statusCode = 400;
    throw error;
  }
}

function normalizeDisplayMode(value) {
  const mode = String(value || 'upcoming').trim().toLowerCase();
  if (mode === 'current' || mode === 'both') {
    return mode;
  }
  return 'upcoming';
}

async function fetchTimetablesData(pool) {
  const [timetableGroups] = await pool.query(`
    SELECT g.id, g.name, g.short_description, g.timezone, g.created_at, g.modified_at, g.created_by, g.modified_by,
           (SELECT COUNT(*) FROM i_timetable_entries e WHERE e.schedule_group_id = g.id) AS entry_count,
           (SELECT MIN(e.start_datetime) FROM i_timetable_entries e WHERE e.schedule_group_id = g.id AND e.start_datetime IS NOT NULL) AS next_start_datetime
    FROM i_timetable_groups g
    ORDER BY g.modified_at DESC, g.id DESC
  `);
  const [timetableEntries] = await pool.query(`
    SELECT id, schedule_group_id, title, short_description, start_datetime, end_datetime, created_at, modified_at, created_by, modified_by
    FROM i_timetable_entries
    ORDER BY schedule_group_id ASC, start_datetime ASC, id ASC
  `);

  const entriesByGroupId = new Map();
  timetableEntries.forEach(function (entry) {
    const groupId = Number(entry.schedule_group_id);
    if (!entriesByGroupId.has(groupId)) {
      entriesByGroupId.set(groupId, []);
    }
    entriesByGroupId.get(groupId).push(entry);
  });

  const groups = timetableGroups.map(function (group) {
    return Object.assign({}, group, {
      entries: entriesByGroupId.get(Number(group.id)) || []
    });
  });

  return {
    timetableGroups: groups,
    timetableEntries: timetableEntries
  };
}

async function fetchTimetableGroupsPage(pool, page, pageSize, searchTerm, sortKey, sortDirection) {
  const paged = await fetchPagedRows(pool, {
    selectSql: `SELECT g.id, g.name, g.short_description, g.timezone, g.created_at, g.modified_at, g.created_by, g.modified_by,
        (SELECT COUNT(*) FROM i_timetable_entries e WHERE e.schedule_group_id = g.id) AS entry_count,
        (SELECT MIN(e.start_datetime) FROM i_timetable_entries e WHERE e.schedule_group_id = g.id AND e.start_datetime IS NOT NULL) AS next_start_datetime
      FROM i_timetable_groups g
    ORDER BY g.modified_at DESC, g.id DESC`,
      countSql: 'SELECT COUNT(*) AS count FROM i_timetable_groups',
    searchColumns: ['g.name', 'g.short_description'],
    searchTerm: searchTerm,
    sortColumns: {
      name: 'g.name',
      description: 'g.short_description',
      timezone: 'g.timezone',
      entries: 'entry_count',
      next_start: 'next_start_datetime',
      created: 'g.created_at',
      modified: 'g.modified_at'
    },
    sortKey: sortKey,
    sortDirection: sortDirection,
    page: page,
    pageSize: pageSize
  });

  return Object.assign({ timetableGroups: paged.rows }, paged);
}

async function fetchTimetableGroupById(pool, id) {
  const [rows] = await pool.query(
    'SELECT id, name, short_description, timezone, created_at, modified_at, created_by, modified_by FROM i_timetable_groups WHERE id = ?',
    [id]
  );

  return rows[0] || null;
}

async function fetchTimetableEntriesByGroupId(pool, timetableGroupId) {
  const [rows] = await pool.query(
    `SELECT id, schedule_group_id, title, short_description, start_datetime, end_datetime, created_at, modified_at, created_by, modified_by
     FROM i_timetable_entries
     WHERE schedule_group_id = ?
     ORDER BY start_datetime ASC, id ASC`,
    [timetableGroupId]
  );

  return rows;
}

function buildTimetableGroupPayload(req, existingTimetableGroup) {
  const fallback = existingTimetableGroup || {};
  const name = validateMaxLength(req.body.name || fallback.name || '', NAME_MAX_LENGTH, 'Timetable group name');
  const shortDescription = validateMaxLength(req.body.short_description || req.body.shortDescription || fallback.short_description || '', DESCRIPTION_MAX_LENGTH, 'Timetable group description');
  const timezone = normalizeTimeZone(req.body.timezone || req.body.time_zone || fallback.timezone || DEFAULT_TIME_ZONE, fallback.timezone || DEFAULT_TIME_ZONE);

  if (!name) {
    const error = new Error('Timetable group name is required.');
    error.statusCode = 400;
    throw error;
  }

  return {
    name: name,
    shortDescription: shortDescription,
    timezone: timezone
  };
}

module.exports = {
  normalizeDisplayMode,
  fetchTimetablesData,
  fetchTimetableGroupsPage,
  fetchTimetableGroupById,
  fetchTimetableEntriesByGroupId,
  buildTimetableGroupPayload,
  normalizeTimeZone
};