/**
 * [Gitea #103] Tracking-parameter stripping.
 *
 * Shared links routinely carry ad/analytics identifiers (`utm_*`, `fbclid`,
 * YouTube `si=`, Amazon `ref=`…) that tie every recipient's click back to the
 * person who shared the link. Everything here is pure and local: a URL goes in,
 * the same URL minus known tracking params comes out. Unknown params are never
 * touched, and anything that fails to parse is returned unchanged.
 */

// Exact query-parameter names stripped on every host.
const GLOBAL_PARAMS = new Set([
  // Google Ads / Analytics
  'gclid',
  'gclsrc',
  'dclid',
  'gbraid',
  'wbraid',
  'srsltid',
  '_ga',
  '_gl',
  // Meta / Instagram
  'fbclid',
  'igshid',
  'igsh',
  // Microsoft / Bing
  'msclkid',
  // X / Twitter
  'twclid',
  // TikTok
  'ttclid',
  // Yandex
  'yclid',
  // Mailchimp
  'mc_cid',
  'mc_eid',
  // HubSpot
  '_hsenc',
  '_hsmi',
  'hsCtaTracking',
  // Marketo / Adobe
  'mkt_tok',
  's_kwcid',
  'ef_id',
  // Vero / Wicked Reports / Omeda
  'vero_id',
  'vero_conv',
  'wickedid',
  'oly_anon_id',
  'oly_enc_id',
  // Generic referrer tags
  'ref_src',
  'ref_url',
  'spm',
]);

// Query-parameter name prefixes stripped on every host.
const GLOBAL_PREFIXES = ['utm_', 'pk_', 'piwik_', 'matomo_'];

// Host-specific params that only act as tracking on that site. Matched by
// hostname suffix (so `www.youtube.com` and `m.youtube.com` both hit `youtube.com`).
const AMAZON_HOSTS = [
  'amazon.com',
  'amazon.co.uk',
  'amazon.de',
  'amazon.ca',
  'amazon.fr',
  'amazon.co.jp',
];

const HOST_PARAMS: Array<{ hosts: string[]; params: string[]; prefixes?: string[] }> = [
  {
    hosts: ['youtube.com', 'youtu.be'],
    params: ['si', 'feature', 'pp'],
  },
  {
    hosts: AMAZON_HOSTS,
    // Affiliate + search-result telemetry only. `th`/`psc` pick the product
    // variant that loads and are deliberately NOT stripped.
    params: [
      'ref',
      'ref_',
      'tag',
      'linkCode',
      'linkId',
      'crid',
      'sprefix',
      'qid',
      'sr',
      'dib',
      'dib_tag',
      'content-id',
    ],
    prefixes: ['pd_rd_', 'pf_rd_'],
  },
  {
    hosts: ['x.com', 'twitter.com'],
    params: ['s', 't', 'ref_src'],
  },
  {
    hosts: ['spotify.com'],
    params: ['si', 'nd'],
  },
  {
    hosts: ['reddit.com'],
    params: ['share_id', 'rdt', 'context'],
  },
  {
    hosts: ['tiktok.com'],
    params: ['_r', '_t', 'is_from_webapp', 'sender_device', 'web_id'],
  },
  {
    hosts: ['instagram.com'],
    params: ['igsh', 'img_index'],
  },
  {
    hosts: ['threads.net'],
    params: ['igshid'],
  },
  {
    hosts: ['bilibili.com'],
    params: ['spm_id_from', 'vd_source'],
  },
  {
    hosts: ['ebay.com', 'ebay.co.uk', 'ebay.de'],
    params: ['_trkparms', '_trksid', 'mkcid', 'mkevt', 'mkrid', 'campid', 'toolid', 'customid'],
  },
];

// Hosts whose URLs are never rewritten: Matrix permalinks encode room/event
// ids after a fragment and have no tracking, but a false positive would break
// navigation, so leave the whole family alone.
const SKIP_HOSTS = ['matrix.to'];

const hostMatches = (hostname: string, suffixes: string[]): boolean =>
  suffixes.some((s) => hostname === s || hostname.endsWith(`.${s}`));

const isTrackingParam = (name: string, hostname: string): boolean => {
  if (GLOBAL_PARAMS.has(name)) return true;
  const lower = name.toLowerCase();
  if (GLOBAL_PREFIXES.some((p) => lower.startsWith(p))) return true;
  return HOST_PARAMS.some(
    (rule) =>
      hostMatches(hostname, rule.hosts) &&
      (rule.params.includes(name) || (rule.prefixes ?? []).some((p) => name.startsWith(p))),
  );
};

/**
 * Remove known tracking query parameters from an `http(s)` URL. Returns the
 * input unchanged when it is not an http(s) URL, cannot be parsed, or has
 * nothing to strip — so callers can compare by identity to know whether
 * anything happened. Never touches the fragment or the path (except Amazon's
 * `/ref=…` path segment, which is a pure referrer tag).
 */
export const stripTrackingParams = (url: string): string => {
  if (!/^https?:\/\//i.test(url)) return url;
  let parsed: URL;
  try {
    parsed = new URL(url);
  } catch {
    return url;
  }
  const hostname = parsed.hostname.toLowerCase();
  if (hostMatches(hostname, SKIP_HOSTS)) return url;

  let changed = false;
  const params = parsed.searchParams;
  Array.from(params.keys()).forEach((name) => {
    if (isTrackingParam(name, hostname)) {
      params.delete(name);
      changed = true;
    }
  });

  if (hostMatches(hostname, AMAZON_HOSTS)) {
    const cleanedPath = parsed.pathname.replace(/\/ref=[^/]*/i, '');
    if (cleanedPath !== parsed.pathname) {
      parsed.pathname = cleanedPath;
      changed = true;
    }
  }

  if (!changed) return url;
  // URLSearchParams re-serialises the remaining query; when it is now empty,
  // drop the dangling `?` entirely.
  if (params.toString() === '') parsed.search = '';
  return parsed.toString();
};

// Matches an http(s) URL inside free text, stopping before whitespace, quotes,
// angle brackets or a closing paren/bracket. Trailing sentence punctuation is
// trimmed separately so "see https://a.b/?utm_source=x." keeps its full stop.
const URL_IN_TEXT = /https?:\/\/[^\s<>"'()[\]]+/gi;
const TRAILING_PUNCT = /[.,;:!?]+$/;

/**
 * Strip tracking params from every http(s) URL found in a block of text (the
 * plaintext `body`, or a pasted clipboard string). Returns the input unchanged
 * if nothing was stripped.
 */
export const stripTrackingParamsInText = (text: string): string => {
  let changed = false;
  const out = text.replace(URL_IN_TEXT, (match) => {
    const punct = match.match(TRAILING_PUNCT)?.[0] ?? '';
    const url = punct ? match.slice(0, -punct.length) : match;
    const cleaned = stripTrackingParams(url);
    if (cleaned === url) return match;
    changed = true;
    return cleaned + punct;
  });
  return changed ? out : text;
};

/**
 * Same as `stripTrackingParamsInText` for an HTML string (`formatted_body`),
 * where `&` inside attribute values and text is escaped as `&amp;`. Each URL is
 * unescaped before stripping and re-escaped after, so the surrounding markup is
 * left byte-for-byte intact.
 */
export const stripTrackingParamsInHtml = (html: string): string => {
  let changed = false;
  const out = html.replace(URL_IN_TEXT, (match) => {
    const punct = match.match(TRAILING_PUNCT)?.[0] ?? '';
    const raw = punct ? match.slice(0, -punct.length) : match;
    const url = raw.replace(/&amp;/g, '&');
    const cleaned = stripTrackingParams(url);
    if (cleaned === url) return match;
    changed = true;
    return cleaned.replace(/&/g, '&amp;') + punct;
  });
  return changed ? out : html;
};