const AuditTrail = require('../models/AuditTrail');
const { sanitizeText } = require('../validation/commonValidation');
const { asyncController } = require('../utils/asyncController');
const { recordAuditTrail } = require('../services/auditTrailService');

const escapeRegex = (value = '') => value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
const PAGE_ANALYTICS_EXCLUDED_MODULES = ['', 'auth', 'system'];
const SOURCE_ADMIN = 'admin';
const SOURCE_CLIENT = 'client';
const ANALYTICS_CACHE_TTL_MS = 60 * 1000;

const analyticsResponseCache = {
  visitorAnalytics: null,
  visitorAnalyticsExpiresAt: 0,
};

const invalidateAnalyticsResponseCache = () => {
  analyticsResponseCache.visitorAnalytics = null;
  analyticsResponseCache.visitorAnalyticsExpiresAt = 0;
};

const toFeatureLabel = (value = '') =>
  String(value)
    .replace(/[-_]+/g, ' ')
    .replace(/\b\w/g, (char) => char.toUpperCase())
    .trim();

const visitorKeyProjection = {
  $let: {
    vars: {
      cleanIp: { $trim: { input: { $ifNull: ['$ip', ''] } } },
      cleanActorId: { $trim: { input: { $ifNull: ['$actorId', ''] } } },
      cleanActorName: { $toLower: { $trim: { input: { $ifNull: ['$actorName', ''] } } } },
    },
    in: {
      $switch: {
        branches: [
          { case: { $ne: ['$$cleanIp', ''] }, then: { $concat: ['ip:', '$$cleanIp'] } },
          { case: { $ne: ['$$cleanActorId', ''] }, then: { $concat: ['actor:', '$$cleanActorId'] } },
          { case: { $ne: ['$$cleanActorName', ''] }, then: { $concat: ['name:', '$$cleanActorName'] } },
        ],
        default: { $concat: ['unknown:', { $toString: '$_id' }] },
      },
    },
  },
};

const toStartOfDay = (dateValue) => {
  const date = new Date(dateValue);
  date.setHours(0, 0, 0, 0);
  return date;
};

const createDateLabels = (days) => {
  const labels = [];
  const cursor = toStartOfDay(new Date());
  cursor.setDate(cursor.getDate() - (days - 1));

  for (let index = 0; index < days; index += 1) {
    labels.push(cursor.toISOString().slice(0, 10));
    cursor.setDate(cursor.getDate() + 1);
  }

  return labels;
};

const parseClientPath = (rawPath = '') => {
  const normalized = sanitizeText(rawPath);
  if (!normalized) return '';

  try {
    const base = normalized.startsWith('/') ? `https://client.local${normalized}` : normalized;
    const parsed = new URL(base);
    return sanitizeText(parsed.pathname || '/').toLowerCase() || '/';
  } catch {
    return '';
  }
};

const clientPathToModule = (path = '') => {
  switch (path) {
    case '/':
      return { module: 'welcome', label: 'Welcome Page' };
    case '/mainmenu':
      return { module: 'main-menu', label: 'Main Menu' };
    case '/announcement':
      return { module: 'announcements', label: 'Announcements' };
    case '/achievement':
      return { module: 'achievements', label: 'Achievements' };
    case '/profile':
      return { module: 'faculty', label: 'Faculty Profile' };
    case '/aboutus':
      return { module: 'about-us', label: 'About Us' };
    case '/admission':
      return { module: 'admission', label: 'Admission' };
    default: {
      const derived = path
        .replace(/^\/+/, '')
        .replace(/\/+$/, '')
        .replace(/\//g, '-')
        .toLowerCase();
      const module = derived || 'client-page';
      return { module, label: toFeatureLabel(module) };
    }
  }
};

const resolveSourceFilter = (sourceValue = '') => {
  if (sourceValue === SOURCE_CLIENT) {
    return { source: SOURCE_CLIENT };
  }
  if (sourceValue === SOURCE_ADMIN) {
    return {
      $or: [
        { source: SOURCE_ADMIN },
        { source: { $exists: false } },
      ],
    };
  }
  return null;
};

const parseBoundedInt = (value, { min, max, fallback }) => {
  const parsed = Number.parseInt(String(value ?? ''), 10);
  if (!Number.isInteger(parsed)) return fallback;
  return Math.min(Math.max(parsed, min), max);
};

const parseDateAtBoundary = (value, boundary) => {
  const normalized = sanitizeText(value);
  if (!normalized) return null;

  const suffix = boundary === 'end' ? 'T23:59:59.999Z' : 'T00:00:00.000Z';
  const date = new Date(`${normalized}${suffix}`);
  if (Number.isNaN(date.getTime())) return null;
  return date;
};

const buildAuditTrailFilter = (query = {}, { includeDateRange = false } = {}) => {
  const moduleFilter = sanitizeText(query.module).toLowerCase();
  const actionFilter = sanitizeText(query.action).toLowerCase();
  const sourceFilter = sanitizeText(query.source).toLowerCase();
  const search = sanitizeText(query.q);

  const filterClauses = [];
  if (moduleFilter) filterClauses.push({ module: moduleFilter });
  if (actionFilter) filterClauses.push({ action: actionFilter });

  const sourceClause = resolveSourceFilter(sourceFilter);
  if (sourceClause) filterClauses.push(sourceClause);

  if (search) {
    const regex = new RegExp(escapeRegex(search), 'i');
    filterClauses.push({ $or: [{ summary: regex }, { endpoint: regex }, { actorName: regex }, { ip: regex }] });
  }

  if (includeDateRange) {
    const fromDate = parseDateAtBoundary(query.from, 'start');
    const toDate = parseDateAtBoundary(query.to, 'end');
    if (fromDate || toDate) {
      const createdAt = {};
      if (fromDate) createdAt.$gte = fromDate;
      if (toDate) createdAt.$lte = toDate;
      filterClauses.push({ createdAt });
    }
  }

  return filterClauses.length === 0
    ? {}
    : filterClauses.length === 1
      ? filterClauses[0]
      : { $and: filterClauses };
};

const csvEscape = (value) => {
  const raw = String(value ?? '');
  const escaped = raw.replace(/"/g, '""');
  return `"${escaped}"`;
};

const getAuditTrails = asyncController(async (req, res) => {
  const hasPaginationQuery = req.query.page !== undefined || req.query.pageSize !== undefined;
  const legacyLimit = parseBoundedInt(req.query.limit, { min: 1, max: 1000, fallback: 120 });
  const page = parseBoundedInt(req.query.page, { min: 1, max: 5000, fallback: 1 });
  const pageSize = parseBoundedInt(req.query.pageSize, { min: 1, max: 100, fallback: 25 });
  const filter = buildAuditTrailFilter(req.query);

  const projection = 'actorName source action module summary endpoint method targetId changedFields hasFile statusCode durationMs ip createdAt';

  if (!hasPaginationQuery) {
    const trails = await AuditTrail.find(filter)
      .sort({ createdAt: -1 })
      .limit(legacyLimit)
      .select(projection)
      .lean();

    res.json(trails);
    return;
  }

  const skip = (page - 1) * pageSize;

  const [total, trails] = await Promise.all([
    AuditTrail.countDocuments(filter),
    AuditTrail.find(filter)
      .sort({ createdAt: -1 })
      .skip(skip)
      .limit(pageSize)
      .select(projection)
      .lean(),
  ]);

  res.json({
    items: trails,
    total,
    page,
    pageSize,
    totalPages: Math.max(1, Math.ceil(total / pageSize)),
  });
}, { defaultStatus: 400 });

const exportAuditTrailsCsv = asyncController(async (req, res) => {
  if (!req.query.from && !req.query.to) {
    return res.status(400).json({ success: false, message: 'A date range (from or to) is required for CSV export.' });
  }

  const filter = buildAuditTrailFilter(req.query, { includeDateRange: true });
  const projection = 'actorName source action module summary endpoint method targetId changedFields hasFile statusCode durationMs ip createdAt';

  const exportCount = await AuditTrail.countDocuments(filter);
  if (exportCount > 50000) {
    return res.status(400).json({ success: false, message: 'Export exceeds 50,000 rows. Please narrow your date range.' });
  }

  const from = (sanitizeText(req.query.from) || 'all').replace(/[^a-z0-9-]/gi, '-').slice(0, 50);
  const to = (sanitizeText(req.query.to) || 'all').replace(/[^a-z0-9-]/gi, '-').slice(0, 50);
  const filename = `audit-trails-${from}-to-${to}.csv`;

  res.setHeader('Content-Type', 'text/csv; charset=utf-8');
  res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
  res.setHeader('Cache-Control', 'no-store');

  // Add UTF-8 BOM for spreadsheet compatibility on kiosk admin workflows.
  res.write('\uFEFF');
  res.write([
    'createdAt',
    'source',
    'actorName',
    'action',
    'module',
    'summary',
    'endpoint',
    'method',
    'targetId',
    'changedFields',
    'hasFile',
    'statusCode',
    'durationMs',
    'ip',
  ].join(',') + '\n');

  const cursor = AuditTrail.find(filter)
    .sort({ createdAt: -1 })
    .select(projection)
    .lean()
    .cursor();

  for await (const item of cursor) {
    const changedFields = Array.isArray(item?.changedFields) ? item.changedFields.join('|') : '';
    const row = [
      csvEscape(item?.createdAt ? new Date(item.createdAt).toISOString() : ''),
      csvEscape(item?.source || ''),
      csvEscape(item?.actorName || ''),
      csvEscape(item?.action || ''),
      csvEscape(item?.module || ''),
      csvEscape(item?.summary || ''),
      csvEscape(item?.endpoint || ''),
      csvEscape(item?.method || ''),
      csvEscape(item?.targetId || ''),
      csvEscape(changedFields),
      csvEscape(Boolean(item?.hasFile)),
      csvEscape(item?.statusCode ?? ''),
      csvEscape(item?.durationMs ?? ''),
      csvEscape(item?.ip || ''),
    ];
    res.write(`${row.join(',')}\n`);
  }

  res.end();
}, { defaultStatus: 400 });

const getVisitorAnalytics = asyncController(async (_req, res) => {
  if (analyticsResponseCache.visitorAnalytics && analyticsResponseCache.visitorAnalyticsExpiresAt > Date.now()) {
    res.json(analyticsResponseCache.visitorAnalytics);
    return;
  }

  const todayStart = toStartOfDay(new Date());
  const sevenDaysStart = toStartOfDay(new Date());
  sevenDaysStart.setDate(sevenDaysStart.getDate() - 6);
  const dailyWindowStart = toStartOfDay(new Date());
  dailyWindowStart.setDate(dailyWindowStart.getDate() - 13);

  // source: SOURCE_CLIENT scopes exclusively to user page-view events
  const filterToday = { source: SOURCE_CLIENT, createdAt: { $gte: todayStart } };
  const filterSevenDays = { source: SOURCE_CLIENT, createdAt: { $gte: sevenDaysStart } };
  const filterDailyWindow = { source: SOURCE_CLIENT, createdAt: { $gte: dailyWindowStart } };

  const [todaysVisitorsAgg, weeklyVisitorsAgg, dailyVisitorsAgg, topPagesAgg] = await Promise.all([
    AuditTrail.aggregate([
      { $match: filterToday },
      { $project: { visitorKey: visitorKeyProjection } },
      { $group: { _id: '$visitorKey' } },
      { $count: 'count' },
    ]),
    AuditTrail.aggregate([
      { $match: filterSevenDays },
      { $project: { visitorKey: visitorKeyProjection } },
      { $group: { _id: '$visitorKey' } },
      { $count: 'count' },
    ]),
    AuditTrail.aggregate([
      { $match: filterDailyWindow },
      {
        $project: {
          day: { $dateToString: { format: '%Y-%m-%d', date: '$createdAt' } },
          visitorKey: visitorKeyProjection,
        },
      },
      { $group: { _id: { day: '$day', visitorKey: '$visitorKey' }, visitorHits: { $sum: 1 } } },
      {
        $group: {
          _id: '$_id.day',
          uniqueVisitors: { $sum: 1 },
          totalHits: { $sum: '$visitorHits' },
        },
      },
      { $sort: { _id: 1 } },
    ]),
    AuditTrail.aggregate([
      {
        $match: {
          ...filterSevenDays,
          module: {
            $exists: true,
            $nin: PAGE_ANALYTICS_EXCLUDED_MODULES,
          },
        },
      },
      {
        $project: {
          module: '$module',
          visitorKey: visitorKeyProjection,
        },
      },
      { $group: { _id: { module: '$module', visitorKey: '$visitorKey' }, hits: { $sum: 1 } } },
      {
        $group: {
          _id: '$_id.module',
          uniqueVisitors: { $sum: 1 },
          totalHits: { $sum: '$hits' },
        },
      },
      { $sort: { totalHits: -1, uniqueVisitors: -1, _id: 1 } },
      { $limit: 8 },
    ]),
  ]);

  const dailyMap = new Map(
    dailyVisitorsAgg.map((item) => [
      item?._id,
      {
        uniqueVisitors: Number(item?.uniqueVisitors || 0),
        totalHits: Number(item?.totalHits || 0),
      },
    ]),
  );

  const dailyVisitors = createDateLabels(14).map((date) => ({
    date,
    uniqueVisitors: Number(dailyMap.get(date)?.uniqueVisitors || 0),
    totalHits: Number(dailyMap.get(date)?.totalHits || 0),
  }));

  const topPages = topPagesAgg.map((item) => ({
    module: sanitizeText(item?._id),
    label: toFeatureLabel(item?._id),
    uniqueVisitors: Number(item?.uniqueVisitors || 0),
    totalHits: Number(item?.totalHits || 0),
  }));

  const todaysVisitors = Number(todaysVisitorsAgg?.[0]?.count || 0);
  const weeklyVisitors = Number(weeklyVisitorsAgg?.[0]?.count || 0);
  const totalDailyVisitors = dailyVisitors.reduce((sum, item) => sum + item.uniqueVisitors, 0);

  const topByHits = [...topPages].sort((a, b) => b.totalHits - a.totalHits)[0];
  const mostUsedFeatureRaw = topByHits?.module || '';
  const mostUsedFeatureCount = topByHits?.totalHits || 0;

  const responsePayload = {
    overview: {
      totalVisitors: weeklyVisitors,
      todaysVisitors,
      weeklyVisitors,
      avgDailyVisitors: Number((totalDailyVisitors / dailyVisitors.length).toFixed(1)),
      mostUsedFeature: mostUsedFeatureRaw ? toFeatureLabel(mostUsedFeatureRaw) : 'No feature data',
      mostUsedFeatureCount,
      hasUsageData: mostUsedFeatureCount > 0,
    },
    dailyVisitors,
    topPages,
    generatedAt: new Date().toISOString(),
  };

  analyticsResponseCache.visitorAnalytics = responsePayload;
  analyticsResponseCache.visitorAnalyticsExpiresAt = Date.now() + ANALYTICS_CACHE_TTL_MS;
  res.json(responsePayload);
}, { defaultStatus: 400 });

const logClientEvent = asyncController(async (req, res) => {
  const path = parseClientPath(req.body?.path);
  if (!path || path.startsWith('/admin')) {
    return res.status(400).json({ message: 'Invalid client path' });
  }

  const { module, label } = clientPathToModule(path);

  if (module === 'welcome') {
    return res.status(200).json({ success: true });
  }

  await recordAuditTrail({
    req,
    source: SOURCE_CLIENT,
    actor: { id: 'client', name: 'Client Visitor' },
    action: 'other',
    moduleName: module,
    summary: `Viewed ${label}`,
    endpoint: `GET ${path}`,
    method: 'GET',
    statusCode: 200,
    durationMs: 0,
  });

  invalidateAnalyticsResponseCache();

  res.status(201).json({ success: true });
}, { defaultStatus: 400 });

module.exports = { getAuditTrails, exportAuditTrailsCsv, getVisitorAnalytics, logClientEvent };