/**
 * Analytics Tracking Middleware
 * Privacy-respecting visitor tracking (no cookies, hashed identifiers)
 */

const crypto = require('crypto');
const { PageView, Session } = require('../models/Analytics.model');

/**
 * Generate visitor ID from IP + User Agent (hashed for privacy)
 */
function generateVisitorId(ip, userAgent) {
  const hash = crypto.createHash('sha256');
  hash.update(`${ip}${userAgent}${process.env.ANALYTICS_SALT || 'tractatus-analytics'}`);
  return hash.digest('hex').substring(0, 32);
}

/**
 * Generate session ID (unique per session)
 */
function generateSessionId() {
  return crypto.randomBytes(16).toString('hex');
}

/**
 * Parse UTM parameters from query string
 */
function parseUTM(query) {
  return {
    utmSource: query.utm_source || null,
    utmMedium: query.utm_medium || null,
    utmCampaign: query.utm_campaign || null,
    utmContent: query.utm_content || null,
    utmTerm: query.utm_term || null
  };
}

/**
 * Analytics tracking middleware
 */
async function trackPageView(req, res, next) {
  // Skip tracking for:
  // - Admin pages
  // - API routes
  // - Static assets
  // - Health checks
  const skipPaths = ['/admin/', '/api/', '/css/', '/js/', '/images/', '/fonts/', '/health'];
  if (skipPaths.some(path => req.path.startsWith(path))) {
    return next();
  }

  // Skip if this is not a page view (only track HTML pages)
  const acceptHeader = req.headers.accept || '';
  if (!acceptHeader.includes('text/html')) {
    return next();
  }

  try {
    // Get visitor information
    const ip = req.ip || req.connection.remoteAddress;
    const userAgent = req.headers['user-agent'] || 'Unknown';
    const visitorId = generateVisitorId(ip, userAgent);

    // Get or create session
    let sessionId = req.cookies?.tractatus_session;
    if (!sessionId) {
      sessionId = generateSessionId();
      // Set session cookie (30 minutes expiry)
      res.cookie('tractatus_session', sessionId, {
        httpOnly: true,
        secure: process.env.NODE_ENV === 'production',
        maxAge: 30 * 60 * 1000, // 30 minutes
        sameSite: 'strict'
      });
    }

    // Parse UTM parameters
    const utm = parseUTM(req.query);

    // Get referrer (external only)
    let referrer = req.headers.referer || req.headers.referrer || '';
    if (referrer) {
      const referrerHost = new URL(referrer).hostname;
      const currentHost = req.hostname;
      if (referrerHost === currentHost) {
        referrer = ''; // Internal referrer, don't track
      }
    }

    // Get language
    const language = req.headers['accept-language']?.split(',')[0] || 'en';

    // Check if this is a unique visitor today
    const startOfDay = new Date();
    startOfDay.setHours(0, 0, 0, 0);
    const existingToday = await PageView.findOne({
      visitorId,
      timestamp: { $gte: startOfDay }
    });
    const isUnique = !existingToday;

    // Create page view record
    const pageView = await PageView.create({
      path: req.path,
      title: null, // Will be updated by client-side script
      referrer,
      visitorId,
      sessionId,
      userAgent,
      language,
      timestamp: new Date(),
      isUnique,
      ...utm
    });

    // Update or create session
    let session = await Session.findOne({ sessionId });
    if (!session) {
      // New session
      session = await Session.create({
        sessionId,
        visitorId,
        startTime: new Date(),
        pageViews: 1,
        pages: [req.path],
        entryPage: req.path,
        referrer,
        language,
        isActive: true,
        ...utm
      });
    } else {
      // Update existing session
      session.pageViews += 1;
      session.pages.push(req.path);
      session.exitPage = req.path;
      session.endTime = new Date();
      session.duration = Math.round((session.endTime - session.startTime) / 1000);
      await session.save();
    }

    // Attach analytics data to request (for potential use in response)
    req.analytics = {
      visitorId,
      sessionId,
      pageViewId: pageView._id
    };

  } catch (error) {
    // Analytics failure should not break the site
    console.error('[Analytics] Tracking error:', error.message);
  }

  next();
}

/**
 * Track page duration (called when user leaves page)
 */
async function trackPageDuration(req, res, next) {
  try {
    const { pageViewId, duration } = req.body;

    if (pageViewId && duration) {
      await PageView.findByIdAndUpdate(pageViewId, {
        duration: parseInt(duration, 10)
      });
    }

    res.json({ success: true });
  } catch (error) {
    console.error('[Analytics] Duration tracking error:', error.message);
    res.status(500).json({ error: 'Failed to track duration' });
  }
}

/**
 * Track page title (called from client-side)
 */
async function trackPageTitle(req, res, next) {
  try {
    const { pageViewId, title } = req.body;

    if (pageViewId && title) {
      await PageView.findByIdAndUpdate(pageViewId, {
        title: title.substring(0, 200) // Limit title length
      });
    }

    res.json({ success: true });
  } catch (error) {
    console.error('[Analytics] Title tracking error:', error.message);
    res.status(500).json({ error: 'Failed to track title' });
  }
}

/**
 * Cleanup old sessions (mark as inactive)
 */
async function cleanupSessions() {
  try {
    const thirtyMinutesAgo = new Date(Date.now() - 30 * 60 * 1000);

    await Session.updateMany(
      {
        isActive: true,
        endTime: { $lt: thirtyMinutesAgo }
      },
      {
        isActive: false
      }
    );
  } catch (error) {
    console.error('[Analytics] Session cleanup error:', error.message);
  }
}

// Run cleanup every 5 minutes
setInterval(cleanupSessions, 5 * 60 * 1000);

module.exports = {
  trackPageView,
  trackPageDuration,
  trackPageTitle,
  cleanupSessions
};