next.config.ts

import type { NextConfig } from 'next';
import createNextIntlPlugin from 'next-intl/plugin';
import bundleAnalyzer from '@next/bundle-analyzer';

const withNextIntl = createNextIntlPlugin('./core/i18n/request.ts');
const withBundleAnalyzer = bundleAnalyzer({
  enabled: process.env.ANALYZE === 'true',
});

const isDev = process.env.NODE_ENV !== 'production';

const posthogHost = process.env.NEXT_PUBLIC_POSTHOG_HOST;
const cspConnectSrc = [
  "'self'",
  'https://www.googletagmanager.com',
  'https://www.google-analytics.com',
  'https://www.clarity.ms',
  'https://vercel-analytics.com',
  'https://vitals.vercel-insights.com',
  'https://translation.googleapis.com',
];

if (posthogHost) {
  cspConnectSrc.push(posthogHost);
}

const cspEnforced =
  "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval' https:; style-src 'self' 'unsafe-inline' https:; img-src 'self' data: blob: https:; font-src 'self' data: https:; connect-src 'self' https:; frame-src 'self' https:; object-src 'none'; base-uri 'self';";

const cspReportOnly = [
  "default-src 'self'",
  "script-src 'self' 'unsafe-inline' 'unsafe-eval' https://www.googletagmanager.com https://www.google-analytics.com https://www.clarity.ms",
  "style-src 'self' 'unsafe-inline' https://fonts.googleapis.com",
  "img-src 'self' data: blob: https:",
  "font-src 'self' data: https://fonts.gstatic.com",
  `connect-src ${cspConnectSrc.join(' ')}`,
  "frame-src 'self' https://www.googletagmanager.com",
  "object-src 'none'",
  "base-uri 'self'",
].join('; ');

const nextConfig: NextConfig = {
  // Performance optimizations
  reactStrictMode: true,
  compress: false, // Let Vercel handle compression
  poweredByHeader: false, // Remove X-Powered-By header for security
  generateEtags: true, // Generate ETags for better caching

  // Disable instrumentation in development
  // instrumentationHook: !isDev,

  // Compiler optimizations
  compiler: {
    removeConsole: !isDev ? { exclude: ['error', 'warn'] } : false,
  },

  // Experimental features for better performance
  experimental: {
    // Faster builds
    // webpackBuildWorker: true
  },

  // Turbopack configuration (moved from experimental.turbo in Next.js 15)
  turbopack: {
    // Resolve aliases for faster module resolution
    resolveAlias: {
      '@/features': './features',
      '@/shared': './shared',
      '@/core': './core',
    },
  },

  // Reduce overhead in development
  devIndicators: false,

  // Optimize images
  images: {
    formats: ['image/avif', 'image/webp'],
    deviceSizes: [640, 750, 828, 1080, 1200, 1920, 2048, 3840],
    imageSizes: [16, 32, 48, 64, 96, 128, 256, 384],
    minimumCacheTTL: 31536000, // 1 year cache for optimized images
    remotePatterns: [
      {
        protocol: 'https',
        hostname: 'avatars.githubusercontent.com',
        pathname: '/u/**',
      },
    ],
  },

  // Skip type checking during dev (run separately with `npm run check`)
  typescript: {
    ignoreBuildErrors: isDev,
  },

  // Skip ESLint during dev builds
  eslint: {
    ignoreDuringBuilds: isDev,
  },

  webpack: (config, { isServer }) => {
    if (!isServer) {
      config.resolve.fallback = {
        ...(config.resolve.fallback ?? {}),
        fs: false,
        path: false,
      };
    }
    return config;
  },

  // Cache headers for static assets - reduces data transfer and edge requests
  async headers() {
    return [
      {
        // Security headers for all routes (enhances Bing trust signals)
        source: '/:path*',
        headers: [
          {
            key: 'X-Content-Type-Options',
            value: 'nosniff',
          },
          {
            key: 'X-Frame-Options',
            value: 'SAMEORIGIN',
          },
          {
            key: 'Referrer-Policy',
            value: 'strict-origin-when-cross-origin',
          },
          {
            key: 'Permissions-Policy',
            value: 'interest-cohort=()',
          },
          {
            key: 'Content-Security-Policy',
            value: cspEnforced,
          },
          {
            key: 'Content-Security-Policy-Report-Only',
            value: cspReportOnly,
          },
          {
            key: 'Cross-Origin-Opener-Policy',
            value: 'same-origin-allow-popups',
          },
          {
            key: 'Cross-Origin-Resource-Policy',
            value: 'same-site',
          },
          {
            key: 'Origin-Agent-Cluster',
            value: '?1',
          },
        ],
      },
      {
        // Audio files - immutable, cache forever
        source: '/sounds/:path*',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=31536000, immutable',
          },
        ],
      },
      {
        // Kanji JSON data files - cache for 1 week
        source: '/data-kanji/:path*.json',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=604800, stale-while-revalidate=86400',
          },
        ],
      },
      {
        // Vocab JSON data files - cache for 1 week
        source: '/data-vocab/:path*.json',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=604800, stale-while-revalidate=86400',
          },
        ],
      },
      {
        // Japan facts API - cache for 1 week
        source: '/api/facts',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=604800, stale-while-revalidate=86400',
          },
        ],
      },
      {
        // Wallpapers and images - immutable
        source: '/wallpapers/:path*',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=31536000, immutable',
          },
        ],
      },
      {
        // Manifest and other static files
        source: '/manifest.json',
        headers: [
          {
            key: 'Cache-Control',
            value: 'public, max-age=86400, stale-while-revalidate=3600',
          },
        ],
      },
    ];
  },
};

export default withBundleAnalyzer(withNextIntl(nextConfig));