import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';

export function middleware(request: NextRequest) {
  const nonce = Buffer.from(crypto.randomUUID()).toString('base64');

  // Define CSP directives
  const cspDirectives = [
    "default-src 'self'",
    // No 'unsafe-inline' fallback: CSP3 browsers ignore it next to a nonce, but
    // CSP2-only browsers ignore 'strict-dynamic' and would honour it — making
    // the fallback strictly worse than having none. There are no inline
    // <script> tags in the app; Next.js nonces the ones it injects itself.
    `script-src 'self' 'nonce-${nonce}' 'strict-dynamic'`,
    "style-src 'self' 'unsafe-inline' https://fonts.googleapis.com https://unpkg.com",
    "font-src 'self' https://fonts.gstatic.com",
    "img-src 'self' data: blob: https://*.basemaps.cartocdn.com https://*.tile.openstreetmap.org https://unpkg.com",
    "connect-src 'self' https://fonts.googleapis.com https://fonts.gstatic.com",
    "frame-ancestors 'none'",
    "base-uri 'self'",
    "form-action 'self'",
  ].join('; ');

  const requestHeaders = new Headers(request.headers);
  requestHeaders.set('x-nonce', nonce);
  requestHeaders.set('Content-Security-Policy', cspDirectives);

  const response = NextResponse.next({
    request: {
      headers: requestHeaders,
    },
  });

  // Only the CSP is set here. Every other security header comes from
  // next.config.ts, which also covers /api and static assets. Setting a header
  // in both places emits it twice with conflicting values.
  response.headers.set('Content-Security-Policy', cspDirectives);

  return response;
}

export const config = {
  matcher: [
    /*
     * Match all request paths except for the ones starting with:
     * - api (API routes — JSON/binary responses, no document CSP needed)
     * - _next/static (static files)
     * - _next/image (image optimization files)
     * - favicon.ico, sitemap.xml, robots.txt (metadata files)
     *
     * /admin is NOT excluded: it is the highest-privilege surface in the app
     * and previously ran with no enforced CSP at all.
     */
    {
      source: '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)',
      missing: [
        { type: 'header', key: 'next-router-prefetch' },
        { type: 'header', key: 'purpose', value: 'prefetch' },
      ],
    },
  ],
};