import { NextRequest, NextResponse } from 'next/server';
import { prisma, projectService } from '@/lib/prisma';
import { analyticsCache } from '@/lib/redis';
import { requireSessionAuth, checkRateLimit, getRateLimitHeaders } from '@/lib/auth';

export async function GET(request: NextRequest) {
  try {
    // Rate limiting - more generous for admin dashboard
    const ip = request.headers.get('x-forwarded-for') || request.headers.get('x-real-ip') || 'unknown';
    if (!checkRateLimit(ip, 20, 60000)) { // 20 requests per minute
      return new NextResponse(
        JSON.stringify({ error: 'Rate limit exceeded' }), 
        { 
          status: 429, 
          headers: { 
            'Content-Type': 'application/json',
            ...getRateLimitHeaders(ip, 20, 60000)
          } 
        }
      );
    }

    // Admin-only endpoint: require explicit admin header AND a valid signed session token
    const isAdminRequest = request.headers.get('x-admin-request') === 'true';
    if (!isAdminRequest) return NextResponse.json({ error: 'Admin access required' }, { status: 403 });
    const authError = requireSessionAuth(request);
    if (authError) return authError;

    // Check cache first (but allow bypass with cache-bust parameter)
    const url = new URL(request.url);
    const bypassCache = url.searchParams.get('nocache') === 'true';
    
    if (!bypassCache) {
      const cachedStats = await analyticsCache.getOverallStats();
      if (cachedStats) {
        return NextResponse.json(cachedStats);
      }
    }

    // Get analytics data
    const projectsResult = await projectService.getAllProjects();
    const projects = projectsResult.projects || projectsResult;
    const performanceStats = await projectService.getPerformanceStats();

    const since = new Date(Date.now() - 30 * 24 * 60 * 60 * 1000);

    // Use DB aggregation instead of loading every PageView row into memory
    const [totalViews, sessionsByIp, viewsByProjectRows] = await Promise.all([
      prisma.pageView.count({ where: { timestamp: { gte: since } } }),
      prisma.pageView.groupBy({
        by: ['ip'],
        where: {
          timestamp: { gte: since },
          ip: { not: null },
        },
        _count: { _all: true },
        _min: { timestamp: true },
        _max: { timestamp: true },
      }),
      prisma.pageView.groupBy({
        by: ['projectId'],
        where: {
          timestamp: { gte: since },
          projectId: { not: null },
        },
        _count: { _all: true },
      }),
    ]);

    const totalSessions = sessionsByIp.length;
    const bouncedSessions = sessionsByIp.filter(s => (s as unknown as { _count?: { _all?: number } })._count?._all === 1).length;
    const bounceRate = totalSessions > 0 ? Math.round((bouncedSessions / totalSessions) * 100) : 0;

    const sessionDurationsMs = sessionsByIp
      .map(s => {
        const count = (s as unknown as { _count?: { _all?: number } })._count?._all ?? 0;
        if (count < 2) return 0;
        const minTs = (s as unknown as { _min?: { timestamp?: Date | null } })._min?.timestamp;
        const maxTs = (s as unknown as { _max?: { timestamp?: Date | null } })._max?.timestamp;
        if (!minTs || !maxTs) return 0;
        return maxTs.getTime() - minTs.getTime();
      })
      .filter(ms => ms > 0);

    const avgSessionDuration = sessionDurationsMs.length > 0
      ? Math.round(sessionDurationsMs.reduce((a, b) => a + b, 0) / sessionDurationsMs.length / 1000)
      : 0;

    const totalUsers = totalSessions;

    const viewsByProject = viewsByProjectRows.reduce((acc, row) => {
      const projectId = row.projectId as number | null;
      if (projectId != null) {
        acc[projectId] = (row as unknown as { _count?: { _all?: number } })._count?._all ?? 0;
      }
      return acc;
    }, {} as Record<number, number>);

    // Calculate analytics metrics
    const analytics = {
      overview: {
        totalProjects: projects.length,
        publishedProjects: projects.filter(p => p.published).length,
        featuredProjects: projects.filter(p => p.featured).length,
        totalViews, // Real views from PageView table
        totalLikes: 0, // Not implemented - no like buttons
        totalShares: 0, // Not implemented - no share buttons
        avgLighthouse: (() => {
          // Only calculate if we have real performance data (not defaults)
          const projectsWithPerf = projects.filter(p => {
            const perf = (p.performance as Record<string, unknown>) || {};
            const lighthouse = perf.lighthouse as number || 0;
            return lighthouse > 0; // Only count projects with actual performance data
          });
          return projectsWithPerf.length > 0
            ? Math.round(projectsWithPerf.reduce((sum, p) => sum + ((p.performance as Record<string, unknown>)?.lighthouse as number || 0), 0) / projectsWithPerf.length)
            : 0;
        })()
      },
      projects: projects.map(project => ({
        id: project.id,
        title: project.title,
        category: project.category,
        difficulty: project.difficulty,
        views: viewsByProject[project.id] || 0, // Only real views from PageView table
        likes: 0, // Not implemented
        shares: 0, // Not implemented
        lighthouse: (() => {
          const perf = (project.performance as Record<string, unknown>) || {};
          const score = perf.lighthouse as number || 0;
          return score > 0 ? score : 0; // Only return if we have real data
        })(),
        published: project.published,
        featured: project.featured,
        createdAt: project.createdAt,
        updatedAt: project.updatedAt
      })),
      categories: performanceStats.byCategory,
      difficulties: performanceStats.byDifficulty,
      performance: {
        avgLighthouse: (() => {
          const projectsWithPerf = projects.filter(p => {
            const perf = (p.performance as Record<string, unknown>) || {};
            return (perf.lighthouse as number || 0) > 0;
          });
          return projectsWithPerf.length > 0
            ? Math.round(projectsWithPerf.reduce((sum, p) => sum + ((p.performance as Record<string, unknown>)?.lighthouse as number || 0), 0) / projectsWithPerf.length)
            : 0;
        })(),
        totalViews, // Real total views
        totalLikes: 0,
        totalShares: 0
      },
      metrics: {
        bounceRate,
        avgSessionDuration,
        pagesPerSession: totalSessions > 0 ? (totalViews / totalSessions).toFixed(1) : '0',
        newUsers: totalUsers,
        totalUsers
      }
    };

    // Cache the results
    await analyticsCache.setOverallStats(analytics);

    return NextResponse.json(analytics);
  } catch (error) {
    console.error('Analytics dashboard error:', error);
    return NextResponse.json(
      { error: 'Failed to fetch analytics data' },
      { status: 500 }
    );
  }
}