/**
 * Server-side link preview API endpoint (Node.js / Astro)
 * Uses linkedom for reliable HTML parsing and automatic entity decoding
 * Returns signed proxy URLs for images from untrusted domains
 */

import {
  checkRateLimit,
  recordRequest,
  getCookieId,
  generateNonce,
  createNonceCookie,
} from '../../utils/rateLimit.ts';
import { signImageUrl } from './image-proxy.ts';
import { parseHTML } from 'linkedom';
import type { APIContext } from 'astro';

interface LinkPreviewMeta {
  url: string;
  title: string | null;
  description: string | null;
  image: string | null;
  siteName: string | null;
  type: string | null;
  video: string | null;
  themeColor: string | null;
}

// Trusted domains that can be loaded client-side
const TRUSTED_DOMAINS = new Set([
  'youtube.com', 'www.youtube.com', 'youtu.be', 'img.youtube.com', 'i.ytimg.com',
  'instagram.com', 'www.instagram.com',
  'twitter.com', 'x.com', 'www.twitter.com', 'pbs.twimg.com', 'abs.twimg.com',
  'twitch.tv', 'www.twitch.tv', 'clips.twitch.tv',
  'spotify.com', 'open.spotify.com',
  'soundcloud.com', 'www.soundcloud.com',
  'vimeo.com', 'www.vimeo.com',
  'imgur.com', 'i.imgur.com',
  'giphy.com', 'media.giphy.com',
  'tenor.com', 'media.tenor.com',
  'gfycat.com',
  'reddit.com', 'www.reddit.com', 'v.redd.it', 'i.redd.it', 'preview.redd.it',
  'github.com', 'gist.github.com', 'raw.githubusercontent.com', 'avatars.githubusercontent.com', 'user-images.githubusercontent.com',
  'codepen.io', 'codesandbox.io',
  'streamable.com', 'medal.tv',
  'discord.com', 'cdn.discordapp.com', 'media.discordapp.net',
  'picsum.photos', 'images.unsplash.com',
]);

function isTrustedDomain(url: string): boolean {
  try {
    const parsed = new URL(url);
    return TRUSTED_DOMAINS.has(parsed.hostname);
  } catch {
    return false;
  }
}

async function getSafeImageUrl(imageUrl: string | null): Promise<string | null> {
  if (!imageUrl) return null;
  if (isTrustedDomain(imageUrl)) return imageUrl;
  const signature = await signImageUrl(imageUrl);
  return `/api/image-proxy?url=${encodeURIComponent(imageUrl)}&sig=${signature}`;
}

function parseMetaTags(html: string, url: string): LinkPreviewMeta {
  const meta: LinkPreviewMeta = {
    url,
    title: null,
    description: null,
    image: null,
    siteName: null,
    type: null,
    video: null,
    themeColor: null,
  };

  const decode = str => str?.replace(/&(#(?:x[0-9a-fA-F]+|\d+)|[a-zA-Z]+);/g,
  (_, e) => e[0]==='#' ? String.fromCharCode(e[1]==='x'?parseInt(e.slice(2),16):parseInt(e.slice(1),10))
                         : ({amp:'&',lt:'<',gt:'>',quot:'"',apos:"'"}[e]||_));

  const { document } = parseHTML(html);


  // Open Graph / Twitter / fallback
  meta.title =
    decode(
      document.querySelector('meta[property="og:title"]')?.getAttribute('content') ||
      document.querySelector('meta[name="twitter:title"]')?.getAttribute('content') ||
      document.querySelector('title')?.textContent || null
    );

  meta.description =
    decode(
        document.querySelector('meta[property="og:description"]')?.getAttribute('content') ||
        document.querySelector('meta[name="twitter:description"]')?.getAttribute('content') ||
        document.querySelector('meta[name="description"]')?.getAttribute('content') || null
    );

  meta.image =
    decode(
        document.querySelector('meta[property="og:image"]')?.getAttribute('content') ||
        document.querySelector('meta[name="twitter:image"]')?.getAttribute('content') || null
    );

  meta.siteName =
      decode(
        document.querySelector('meta[property="og:site_name"]')?.getAttribute('content') ||
        new URL(url).hostname.replace(/^www\./, '')
      );
      
  meta.type =
    decode(
      document.querySelector('meta[property="og:type"]')?.getAttribute('content') || null
    );

  meta.video =
    decode(
      document.querySelector('meta[property="og:video"]')?.getAttribute('content') || null
    );

  meta.themeColor =
    decode(
      document.querySelector('meta[name="theme-color"]')?.getAttribute('content') || null
    );

  // Resolve relative image URLs
  if (meta.image && !meta.image.startsWith('http')) {
    try {
      meta.image = decode(new URL(meta.image, new URL(url).origin).href);
    } catch {
      meta.image = null;
    }
  }

  return meta;
}

export async function GET({ request }) {
  // Rate limit
  const rateCheck = checkRateLimit(request, {
    limit: 10,
    windowMs: 1000,
    burstLimit: 50,
    burstWindowMs: 10_000,
  });

  let cookieId = getCookieId(request);
  const hadCookie = !!cookieId;
  if (!cookieId) cookieId = generateNonce();

  if (!rateCheck.allowed) {
    const errorMsg = rateCheck.isFlooding
      ? { error: 'Too many requests - please slow down' }
      : { error: 'Rate limit exceeded' };
    const resp = new Response(JSON.stringify(errorMsg), {
      status: 429,
      headers: { 'Content-Type': 'application/json', 'Retry-After': '1' },
    });
    if (!hadCookie) resp.headers.set('Set-Cookie', createNonceCookie(cookieId));
    return resp;
  }

  recordRequest(request, 1000);

  const url = new URL(request.url);
  const targetUrl = url.searchParams.get('url');

  if (!targetUrl) {
    return new Response(JSON.stringify({ error: 'Missing url parameter' }), {
      status: 400,
      headers: { 'Content-Type': 'application/json' },
    });
  }

  // Validate URL
  let parsedUrl;
  try {
    parsedUrl = new URL(targetUrl);
    if (!['http:', 'https:'].includes(parsedUrl.protocol)) throw new Error();
  } catch {
    return new Response(JSON.stringify({ error: 'Invalid URL' }), {
      status: 400,
      headers: { 'Content-Type': 'application/json' },
    });
  }

  const trusted = isTrustedDomain(targetUrl);

  try {
    const controller = new AbortController();
    const timeout = setTimeout(() => controller.abort(), 8000);

    const response = await fetch(targetUrl, {
      method: 'GET',
      headers: {
        'User-Agent': 'Mozilla/5.0 (compatible; DiscordBot/2.0; +https://discordapp.com)',
        'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
        'Accept-Language': 'en-US,en;q=0.5',
      },
      signal: controller.signal,
      redirect: 'follow',
    });

    clearTimeout(timeout);

    if (!response.ok) {
      return new Response(JSON.stringify({ 
        error: 'Failed to fetch URL',
        status: response.status 
      }), {
        status: 502,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    const contentType = response.headers.get('content-type') || '';

    // Handle direct image
    if (contentType.startsWith('image/')) {
      const safeImageUrl = await getSafeImageUrl(targetUrl);
      const result = { url: targetUrl, type: 'image', image: safeImageUrl, trusted };
      const resp = new Response(JSON.stringify(result), {
        status: 200,
        headers: { 'Content-Type': 'application/json', 'Cache-Control': 'public, max-age=3600' },
      });
      if (!hadCookie) resp.headers.set('Set-Cookie', createNonceCookie(cookieId));
      return resp;
    }

    // Handle direct video
    if (contentType.startsWith('video/')) {
      if (!trusted) {
        return new Response(JSON.stringify({ error: 'Untrusted video source' }), {
          status: 403,
          headers: { 'Content-Type': 'application/json' },
        });
      }
      const result = { url: targetUrl, type: 'video', video: targetUrl, trusted };
      const resp = new Response(JSON.stringify(result), {
        status: 200,
        headers: { 'Content-Type': 'application/json', 'Cache-Control': 'public, max-age=3600' },
      });
      if (!hadCookie) resp.headers.set('Set-Cookie', createNonceCookie(cookieId));
      return resp;
    }

    if (!contentType.includes('text/html') && !contentType.includes('application/xhtml')) {
      return new Response(JSON.stringify({ error: 'URL is not an HTML page', contentType }), {
        status: 400,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    // Read first 50KB
    const reader = response.body.getReader();
    let html = '';
    let bytesRead = 0;
    const maxBytes = 50 * 1024;

    while (bytesRead < maxBytes) {
      const { done, value } = await reader.read();
      if (done) break;
      html += new TextDecoder().decode(value);
      bytesRead += value.length;
      if (html.includes('</head>')) break;
    }
    reader.cancel();

    const meta = parseMetaTags(html, targetUrl);
    meta.trusted = trusted;

    // Convert image to safe URL
    if (meta.image) meta.image = await getSafeImageUrl(meta.image);

    const resp = new Response(JSON.stringify(meta), {
      status: 200,
      headers: { 'Content-Type': 'application/json', 'Cache-Control': 'public, max-age=3600' },
    });
    if (!hadCookie) resp.headers.set('Set-Cookie', createNonceCookie(cookieId));
    return resp;

  } catch (err) {
    console.error('[link-preview] Error fetching URL:', err.message);
    // Don't expose internal error details to client
    return new Response(JSON.stringify({ error: 'Failed to fetch preview' }), {
      status: 500,
      headers: { 'Content-Type': 'application/json' },
    });
  }
}