/**
 * CRA serves one index.html for every route. A canonical in that shared file
 * would point every page at the homepage. After `react-scripts build`, write a
 * copy per route whose canonical href is that route's own absolute URL.
 */
const fs = require('fs');
const path = require('path');
const { ORIGIN, OG_IMAGE, PAGE_PATHS, h1ForPath, titleForPath, descriptionForPath } = require('../src/llm-fe/utils/canonicals');
const { relatedNavHtml } = require('../src/llm-fe/utils/internalLinks');
const { proseHtml } = require('../src/llm-fe/utils/pageProse');
const { jsonLdHtml } = require('../src/llm-fe/utils/structuredData');

const CANONICAL_RE = /<link\s+rel=["']canonical["']\s+href=["'][^"']*["']\s*\/?>/i;
const H1_RE = /<h1[^>]*>[\s\S]*?<\/h1>/i;
const TITLE_RE = /<title>[^<]*<\/title>/i;
const DESCRIPTION_RE = /<meta\s+name=["']description["']\s+content=["'][^"']*["']\s*\/?>/i;
const RELATED_NAV_RE = /<nav\s+aria-label=["']Related pages["']>[\s\S]*?<\/nav>/i;
const PROSE_RE = /<div id="crawler-prose">[\s\S]*?<\/div>/i;
const JSONLD_SOURCE = '<script type="application\\/ld\\+json">[\\s\\S]*?<\\/script>';

/**
 * @param {string} html
 * @param {'property' | 'name'} attr
 * @param {string} key
 * @param {string} content
 * @returns {string}
 */
function replaceSocial(html, attr, key, content) {
  const re = new RegExp(
    `<meta\\s+${attr}=["']${key}["']\\s+content=["'][^"']*["']\\s*\\/?>`,
    'i',
  );
  if (!re.test(html)) {
    throw new Error(`missing meta ${attr}="${key}"`);
  }
  return html.replace(re, () => `<meta ${attr}="${key}" content="${content}" />`);
}

/**
 * @param {string} homeHtml
 * @param {string} pathname
 * @returns {string}
 */
function htmlForPath(homeHtml, pathname) {
  const found = homeHtml.match(new RegExp(CANONICAL_RE.source, 'gi'));
  if (!found || found.length !== 1) {
    throw new Error(
      `expected exactly one <link rel="canonical"> in index.html, found ${found ? found.length : 0}`,
    );
  }
  const url = `${ORIGIN}${pathname}`;
  let next = homeHtml.replace(CANONICAL_RE, `<link rel="canonical" href="${url}" />`);
  const h1s = next.match(/<h1\b/gi);
  if (!h1s || h1s.length !== 1) {
    throw new Error(`expected exactly one <h1> in index.html, found ${h1s ? h1s.length : 0}`);
  }
  const headline = h1ForPath(pathname);
  if (!headline) {
    throw new Error(`no h1 for ${pathname}`);
  }
  next = next.replace(H1_RE, `<h1>${headline}</h1>`);
  if (next.match(/<h1\b/gi).length !== 1) {
    throw new Error(`stamped ${pathname} does not have exactly one h1`);
  }
  const titles = next.match(/<title\b/gi);
  if (!titles || titles.length !== 1) {
    throw new Error(`expected exactly one <title> in index.html, found ${titles ? titles.length : 0}`);
  }
  const title = titleForPath(pathname);
  if (!title) {
    throw new Error(`no title for ${pathname}`);
  }
  next = next.replace(TITLE_RE, `<title>${title}</title>`);
  if (next.match(/<title\b/gi).length !== 1) {
    throw new Error(`stamped ${pathname} does not have exactly one title`);
  }
  const descriptions = next.match(/<meta\s+name=["']description["']/gi);
  if (!descriptions || descriptions.length !== 1) {
    throw new Error(
      `expected exactly one meta description in index.html, found ${descriptions ? descriptions.length : 0}`,
    );
  }
  const description = descriptionForPath(pathname);
  if (!description) {
    throw new Error(`no description for ${pathname}`);
  }
  next = next.replace(DESCRIPTION_RE, `<meta name="description" content="${description}" />`);
  if (next.match(/<meta\s+name=["']description["']/gi).length !== 1) {
    throw new Error(`stamped ${pathname} does not have exactly one meta description`);
  }
  next = replaceSocial(next, 'property', 'og:title', title);
  next = replaceSocial(next, 'property', 'og:description', description);
  next = replaceSocial(next, 'property', 'og:url', url);
  next = replaceSocial(next, 'name', 'twitter:title', title);
  next = replaceSocial(next, 'name', 'twitter:description', description);
  if (!next.includes(`property="og:image" content="${OG_IMAGE}"`)) {
    throw new Error(`stamped ${pathname} is missing the 1200x630 og:image`);
  }
  if (!next.includes('name="twitter:card" content="summary_large_image"')) {
    throw new Error(`stamped ${pathname} is missing twitter:card`);
  }
  const prose = proseHtml(pathname);
  if (PROSE_RE.test(next)) {
    next = next.replace(PROSE_RE, () => prose);
  } else {
    next = next.replace(/<\/h1>/i, () => `</h1>${prose}`);
  }
  const nav = relatedNavHtml(pathname);
  if (RELATED_NAV_RE.test(next)) {
    next = next.replace(RELATED_NAV_RE, () => nav);
  } else {
    next = next.replace(/<\/h1>/i, () => `</h1>${nav}`);
  }
  if (next.match(/<nav\s+aria-label=["']Related pages["']/gi)?.length !== 1) {
    throw new Error(`stamped ${pathname} does not have exactly one related-pages nav`);
  }
  const block = jsonLdHtml(pathname);
  const jsonLdRe = new RegExp(JSONLD_SOURCE, 'gi');
  const existing = next.match(jsonLdRe);
  if (existing) {
    let replaced = false;
    next = next.replace(new RegExp(JSONLD_SOURCE, 'gi'), () => {
      if (replaced) return '';
      replaced = true;
      return block;
    });
  } else {
    next = next.replace(/<\/head>/i, () => `${block}\n</head>`);
  }
  const scripts = next.match(/<script type="application\/ld\+json">/gi);
  if (!scripts || scripts.length !== 1) {
    throw new Error(`stamped ${pathname} should have one JSON-LD script, found ${scripts ? scripts.length : 0}`);
  }
  const parsed = JSON.parse(next.match(/<script type="application\/ld\+json">([\s\S]*?)<\/script>/i)[1]);
  const page = parsed['@graph'] ? parsed['@graph'].find((node) => node['@type'] === 'WebPage') : parsed;
  if (!page || page.headline !== title) {
    throw new Error(`JSON-LD headline for ${pathname} does not match the title`);
  }
  return next;
}

/**
 * @param {string} buildDir
 * @param {string} pathname
 * @returns {string}
 */
function destForPath(buildDir, pathname) {
  if (pathname === '/') return path.join(buildDir, 'index.html');
  if (pathname.endsWith('/')) {
    return path.join(buildDir, pathname.slice(1), 'index.html');
  }
  // Exact URI with no extension. nginx serves these with default_type text/html
  // so /document_storage is this file, not the SPA fallback.
  return path.join(buildDir, pathname.slice(1));
}

/**
 * @param {string} buildDir
 */
function stampCanonicals(buildDir) {
  const indexPath = path.join(buildDir, 'index.html');
  const homeHtml = fs.readFileSync(indexPath, 'utf8');
  for (const pathname of PAGE_PATHS) {
    const dest = destForPath(buildDir, pathname);
    fs.mkdirSync(path.dirname(dest), { recursive: true });
    fs.writeFileSync(dest, htmlForPath(homeHtml, pathname));
  }
}

module.exports = { htmlForPath, destForPath, stampCanonicals, CANONICAL_RE };

if (require.main === module) {
  const buildDir = process.argv[2] || path.resolve(__dirname, '../build');
  stampCanonicals(buildDir);
}