antisocial/src/platforms/reddit.ts

import type { Page } from 'playwright';
import { ResolveError, oneSegment, type Comment, type Media, type Post } from '../types.ts';
import { readOpenGraph } from '../browser/capture.ts';
import { stripTracking } from './url.ts';
import type { PlatformSpec, ResolveContext } from './types.ts';

const HOST = 'https://www.reddit.com';

/** Path roots that are really Reddit paths, so anything else that arrives as
 *  a single opaque segment is a `redd.it` share code. */
const KNOWN_ROOTS = new Set(['r', 'u', 'user', 'comments', 'gallery', 'media', 'wiki']);

type Listing<T> = { kind?: string; data?: { children?: Array<Thing<T>> } };
type Thing<T> = { kind?: string; data?: T };

type RedditVideo = {
  fallback_url?: string;
  hls_url?: string;
  has_audio?: boolean;
  width?: number;
  height?: number;
  duration?: number;
};

type MediaMeta = {
  status?: string;
  e?: string;
  m?: string;
  s?: { u?: string; gif?: string; mp4?: string; x?: number; y?: number };
};

type Link = {
  title?: string;
  author?: string;
  subreddit_name_prefixed?: string;
  created_utc?: number;
  selftext?: string;
  permalink?: string;
  url?: string;
  url_overridden_by_dest?: string;
  domain?: string;
  post_hint?: string;
  is_self?: boolean;
  is_video?: boolean;
  is_gallery?: boolean;
  over_18?: boolean;
  spoiler?: boolean;
  link_flair_text?: string | null;
  num_comments?: number;
  score?: number;
  gallery_data?: { items?: Array<{ media_id?: string }> };
  media_metadata?: Record<string, MediaMeta>;
  secure_media?: { reddit_video?: RedditVideo } | null;
  media?: { reddit_video?: RedditVideo } | null;
  preview?: {
    images?: Array<{ source?: { url?: string; width?: number; height?: number } }>;
    reddit_video_preview?: RedditVideo;
  };
  crosspost_parent_list?: Link[];
};

type CommentData = {
  author?: string;
  body?: string;
  media_metadata?: Record<string, MediaMeta>;
  created_utc?: number;
  score?: number;
  score_hidden?: boolean;
  is_submitter?: boolean;
  distinguished?: string | null;
  replies?: Listing<CommentData> | '';
};

type MoreData = { count?: number };

/** `[deleted]` and `[removed]` are the platform's own words, kept as they are. */
function authorName(author: string | undefined): string {
  if (!author || author.startsWith('[')) return author ?? '[unknown]';
  return `u/${author}`;
}

function isoFrom(seconds: number | undefined): string | undefined {
  return seconds ? new Date(seconds * 1000).toISOString() : undefined;
}

function sized(width: number | undefined, height: number | undefined) {
  return {
    ...(width ? { width } : {}),
    ...(height ? { height } : {}),
  };
}

/**
 * Reddit's own video, which arrives in three forms at once.
 *
 * `fallback_url` is a plain MP4 and the nicer thing to serve — it proxies,
 * so the viewer never talks to Reddit, and the native scrubber can seek it.
 * But when a post has sound that MP4 is the video track alone: the audio is
 * a separate file the DASH manifest stitches back on. So a silent post gets
 * the MP4 and one with audio gets the HLS playlist, linked directly because
 * proxying it would mean rewriting the manifest and every segment.
 */
function fromRedditVideo(video: RedditVideo, poster: string | undefined): Media[] {
  const common = {
    ...sized(video.width, video.height),
    ...(video.duration ? { durationSec: video.duration } : {}),
    // The still belongs to the video and not to the format it is served in.
    // The HLS branch used to drop it, which is why a post with sound showed
    // an empty box where every silent one showed a frame.
    ...(poster ? { poster: { url: poster } } : {}),
  };

  if (video.has_audio !== false && video.hls_url) {
    return [{ kind: 'video', url: video.hls_url, hls: true, direct: true, ...common }];
  }
  const url = video.fallback_url ?? video.hls_url;
  if (!url) return [];
  if (url === video.hls_url) {
    return [{ kind: 'video', url, hls: true, direct: true, ...common }];
  }
  return [{ kind: 'video', url, ...common }];
}

/** One entry of a gallery post. Reddit keeps the pictures somewhere other
 *  than the order it wants them shown in, so the two have to be joined. */
function fromGalleryItem(meta: MediaMeta | undefined): Media[] {
  if (!meta || meta.status !== 'valid') return [];
  const size = sized(meta.s?.x, meta.s?.y);

  // An animated entry ships as a video as well; that is smaller and seekable.
  if (meta.s?.mp4) return [{ kind: 'video', url: meta.s.mp4, ...size }];
  const url = meta.s?.gif ?? meta.s?.u;
  return url ? [{ kind: 'image', url, ...size }] : [];
}

export function mediaFromLink(link: Link): Media[] {
  // A crosspost is a wrapper with nothing of its own in it.
  const crossposted = link.crosspost_parent_list?.[0];
  if (crossposted && !link.is_self) {
    const inner = mediaFromLink(crossposted);
    if (inner.length) return inner;
  }

  // `scrubber_media_url` looks like a poster and is not one: it is a second,
  // tiny MP4 for the timeline thumbnails. The still is in the preview.
  const still = link.preview?.images?.[0]?.source?.url;

  const video = link.secure_media?.reddit_video ?? link.media?.reddit_video;
  if (video) return fromRedditVideo(video, still);

  if (link.is_gallery) {
    const items = link.gallery_data?.items ?? [];
    const gallery = items.flatMap((item) =>
      fromGalleryItem(item.media_id ? link.media_metadata?.[item.media_id] : undefined));
    if (gallery.length) return gallery;
  }

  // A GIF link is served as a video by the preview, which is the version
  // worth having: the original is often tens of megabytes.
  const asVideo = link.preview?.reddit_video_preview;
  if (asVideo) return fromRedditVideo(asVideo, still);

  const direct = link.url_overridden_by_dest ?? link.url;
  if (direct && /\.(jpe?g|png|webp|gif)(\?|$)/i.test(direct)) {
    const source = link.preview?.images?.[0]?.source;
    return [{ kind: 'image', url: direct, ...sized(source?.width, source?.height) }];
  }

  // A link to somewhere else: the preview is all Reddit has, and it is still
  // worth showing above the link itself.
  const preview = link.preview?.images?.[0]?.source;
  if (preview?.url) {
    return [{ kind: 'image', url: preview.url, ...sized(preview.width, preview.height) }];
  }

  return [];
}

/**
 * The words of the post: the self text, or — for a link post — the
 * destination, which is the whole content of the post and needs to be
 * tappable.
 */
function bodyOf(link: Link): string | undefined {
  if (link.selftext?.trim()) return link.selftext;
  const dest = link.url_overridden_by_dest;
  if (dest && !dest.includes('redd.it') && !dest.startsWith(`${HOST}/gallery/`)) return dest;
  return undefined;
}

/** The whole of `![...](...)`, with the target captured. */
const INLINE_IMAGE = /!\[([^\]\n]*)\]\(([^)\s]+)\)/g;

/**
 * A Giphy token, which unlike the others says what it points at.
 *
 * Reddit writes a variant name after the id on some of them
 * (`giphy|abc123|downsized`); only the id is kept, because Giphy does not
 * serve every variant for every gif but always serves the full one.
 */
const GIPHY_TOKEN = /^giphy\|([A-Za-z0-9]+)(?:\|[a-z_]+)?$/;

/**
 * Point a comment's inline images at something fetchable.
 *
 * Reddit writes them as `![gif](giphy|Ve7wX45)`, `![img](emote|t5_2th52|4358)`
 * or `![img](jo8gf0ca92zd1)` — a token rather than an address. Usually the
 * token is a key in that same comment's `media_metadata`, which is where the
 * real URL is, so one lookup covers all three and none of them needs naming
 * here.
 *
 * Usually, not always: Reddit ships plenty of comments carrying a Giphy token
 * and no `media_metadata` at all, and with nothing to look the token up in
 * those showed the token itself where the gif should have been. Giphy is the
 * one kind that can be resolved without the lookup, the id in it being Giphy's
 * own, so it falls back to Giphy's address for that id. The other two cannot:
 * their ids mean nothing off Reddit.
 *
 * A target that is already an address is not a key, so it falls through
 * untouched.
 */
export function resolveInlineImages(
  body: string,
  meta: Record<string, MediaMeta> | undefined,
): string {
  return body.replace(INLINE_IMAGE, (whole, alt: string, token: string) => {
    const entry = meta?.[token];
    if (entry?.status === 'valid') {
      // An animated one has both; the GIF plays in an `<img>` on its own,
      // which an MP4 does not.
      const url = entry.s?.gif ?? entry.s?.u;
      if (url) return `![${alt}](${url})`;
    }

    const giphy = GIPHY_TOKEN.exec(token)?.[1];
    return giphy ? `![${alt}](https://i.giphy.com/media/${giphy}/giphy.gif)` : whole;
  });
}

export function commentsFrom(listing: Listing<CommentData> | undefined): {
  comments: Comment[];
  more: number;
} {
  const comments: Comment[] = [];
  let more = 0;

  for (const child of listing?.data?.children ?? []) {
    if (child.kind === 'more') {
      more += (child.data as MoreData | undefined)?.count ?? 0;
      continue;
    }
    const data = child.data;
    if (!data || data.body === undefined) continue;

    const replies = data.replies && typeof data.replies === 'object'
      ? commentsFrom(data.replies)
      : { comments: [], more: 0 };

    comments.push({
      author: authorName(data.author),
      ...(data.body ? { text: resolveInlineImages(data.body, data.media_metadata) } : {}),
      ...(isoFrom(data.created_utc) ? { postedAt: isoFrom(data.created_utc) } : {}),
      // Reddit hides the score on a new comment so an early downvote cannot
      // steer the rest. Showing a placeholder 1 would be a lie.
      ...(data.score_hidden !== true && typeof data.score === 'number' ? { score: data.score } : {}),
      ...(data.is_submitter ? { isAuthor: true } : {}),
      ...(data.distinguished ? { distinguished: data.distinguished } : {}),
      replies: replies.comments,
      ...(replies.more ? { moreReplies: replies.more } : {}),
    });
  }

  return { comments, more };
}

export function toPost(body: [Listing<Link>, Listing<CommentData>], originalUrl: string): Post {
  const link = body[0]?.data?.children?.[0]?.data;
  if (!link) throw new ResolveError('Reddit returned no post', 'reddit', originalUrl);

  const { comments, more } = commentsFrom(body[1]);
  const flags = [
    link.link_flair_text?.trim(),
    link.over_18 ? 'NSFW' : undefined,
    link.spoiler ? 'Spoiler' : undefined,
  ].filter(Boolean);

  return {
    platform: 'reddit',
    platformLabel: 'Reddit',
    originalUrl,
    author: {
      // The subreddit is the identity a Reddit link carries — the poster is
      // a detail underneath it, so it goes in the display name.
      handle: link.subreddit_name_prefixed ?? 'reddit',
      displayName: [authorName(link.author), ...flags].join(' · '),
    },
    textPosition: 'above',
    segments: oneSegment({
      ...(link.title ? { title: link.title } : {}),
      ...(bodyOf(link) ? { text: bodyOf(link) } : {}),
      media: mediaFromLink(link),
      ...(isoFrom(link.created_utc) ? { postedAt: isoFrom(link.created_utc) } : {}),
    }),
    comments,
    ...(more ? { moreComments: more } : {}),
    ...(typeof link.num_comments === 'number' ? { commentCount: link.num_comments } : {}),
  };
}

export type FlatComment = {
  depth: number;
  author: string;
  score: number;
  created: string;
  text: string;
};

/**
 * Rebuild the nesting from a flat list of comments that each know only their
 * own depth, which is how the rendered page presents them.
 */
export function treeFromDepths(flat: FlatComment[]): Comment[] {
  const roots: Comment[] = [];
  // The comment last seen at each depth, so a reply can be attached to
  // whatever it appeared underneath.
  const openAt: Comment[] = [];

  for (const row of flat) {
    if (!row.text) continue;
    const comment: Comment = {
      author: authorName(row.author),
      text: row.text,
      ...(row.created && !Number.isNaN(Date.parse(row.created))
        ? { postedAt: new Date(row.created).toISOString() }
        : {}),
      ...(Number.isFinite(row.score) ? { score: row.score } : {}),
      replies: [],
    };

    const parent = openAt[row.depth - 1];
    if (row.depth > 0 && parent) parent.replies.push(comment);
    else roots.push(comment);
    // Anything deeper belonged to the comment this one just replaced.
    openAt.length = row.depth + 1;
    openAt[row.depth] = comment;
  }

  return roots;
}

/**
 * Reads the comment tree back out of the rendered page.
 *
 * The floor, for when the JSON is refused. Reddit renders every comment as a
 * `<shreddit-comment>` carrying its own depth, flat in document order.
 */
async function commentsFromDom(page: Page): Promise<Comment[]> {
  const flat = await page
    .evaluate(() =>
      [...document.querySelectorAll('shreddit-comment')].map((el) => ({
        depth: Number(el.getAttribute('depth') ?? 0),
        author: el.getAttribute('author') ?? '',
        score: Number(el.getAttribute('score') ?? Number.NaN),
        created: el.getAttribute('created') ?? '',
        text: el.querySelector('[slot="comment"]')?.textContent?.trim() ?? '',
      })))
    .catch((): FlatComment[] => []);

  return treeFromDepths(flat);
}

/** Whatever the page will admit to, when the JSON will not come. */
async function fromPage(page: Page, originalUrl: string): Promise<Post> {
  const attrs = await page
    .evaluate(() => {
      const post = document.querySelector('shreddit-post');
      if (!post) return null;
      const get = (name: string): string | undefined => post.getAttribute(name) ?? undefined;
      return {
        title: get('post-title'),
        author: get('author'),
        subreddit: get('subreddit-prefixed-name'),
        created: get('created-timestamp'),
        score: get('score'),
        comments: get('comment-count'),
        image: get('content-href'),
      };
    })
    .catch(() => null);

  const og = await readOpenGraph(page);
  const title = attrs?.title ?? og['og:title'];
  if (!title) throw new ResolveError('Reddit served neither the post nor its data', 'reddit', originalUrl);

  const image = attrs?.image ?? og['og:image'];
  const media: Media[] =
    image && /\.(jpe?g|png|webp|gif)(\?|$)/i.test(image) ? [{ kind: 'image', url: image }] : [];

  const count = Number(attrs?.comments);
  return {
    platform: 'reddit',
    platformLabel: 'Reddit',
    originalUrl,
    author: {
      handle: attrs?.subreddit ?? 'reddit',
      displayName: authorName(attrs?.author),
    },
    textPosition: 'above',
    segments: oneSegment({
      title,
      media,
      ...(attrs?.created && !Number.isNaN(Date.parse(attrs.created))
        ? { postedAt: new Date(attrs.created).toISOString() }
        : {}),
    }),
    comments: await commentsFromDom(page),
    ...(Number.isFinite(count) ? { commentCount: count } : {}),
  };
}

/** The `.json` twin of a post URL, asked for at the size of one page. */
function jsonUrlFor(postUrl: string): string {
  const url = new URL(postUrl);
  url.pathname = `${url.pathname.replace(/\/+$/, '')}/.json`;
  url.search = '';
  url.searchParams.set('raw_json', '1');
  url.searchParams.set('limit', '100');
  url.searchParams.set('sort', 'confidence');
  return url.href;
}

function isShareLink(url: URL): boolean {
  return url.hostname === 'redd.it' || /^\/r\/[^/]+\/s\/[^/]+/.test(url.pathname);
}

/**
 * Share links from the app are opaque, and the post id is only on the other
 * side of a redirect. One request that is told not to follow it is enough —
 * far cheaper than loading the page to find out where it went.
 */
async function followShareLink(page: Page, originalUrl: string): Promise<string> {
  const response = await page.request
    .get(originalUrl, { maxRedirects: 0 })
    .catch(() => undefined);
  const location = response?.headers()['location'];
  if (!location) return originalUrl;
  try {
    return stripTracking(new URL(location, originalUrl)).href;
  } catch {
    return originalUrl;
  }
}

async function fetchJson(page: Page, url: string): Promise<[Listing<Link>, Listing<CommentData>] | undefined> {
  const response = await page.request
    .get(url, { headers: { Accept: 'application/json' } })
    .catch(() => undefined);
  if (!response?.ok()) return undefined;
  if (!response.headers()['content-type']?.includes('json')) return undefined;
  const body = (await response.json().catch(() => undefined)) as unknown;
  return Array.isArray(body) && body.length >= 2 ? (body as [Listing<Link>, Listing<CommentData>]) : undefined;
}

async function resolve({ page, originalUrl }: ResolveContext): Promise<Post> {
  let postUrl = originalUrl;
  try {
    if (isShareLink(new URL(originalUrl))) postUrl = await followShareLink(page, originalUrl);
  } catch {
    // Not a URL we can take apart; the request below will say so.
  }

  // Reddit's JSON is the whole post and the whole first page of comments in
  // one response, which no amount of reading the page can match.
  let body = await fetchJson(page, jsonUrlFor(postUrl));

  if (!body) {
    // A cold context gets a JavaScript challenge instead, which the page
    // solves by itself on any ordinary navigation. Doing that once leaves the
    // cookie behind and the JSON answers from then on, including for every
    // later post.
    await page.goto(postUrl, { waitUntil: 'domcontentloaded' }).catch(() => undefined);
    await page.waitForTimeout(1500);
    body = await fetchJson(page, jsonUrlFor(page.url() || postUrl));

    if (!body) {
      // Still refused. The page in front of us is the post, so read that.
      await page.waitForSelector('shreddit-comment', { timeout: 5_000 }).catch(() => undefined);
      return fromPage(page, originalUrl);
    }
  }

  // The resolved permalink, not the share code we came in with: an opaque
  // `/s/` link says nothing about what it points at, and handing it back is
  // the same as handing back a tracking parameter.
  return toPost(body, postUrl);
}

export const reddit: PlatformSpec = {
  id: 'reddit',
  label: 'Reddit',
  prefix: 'reddit',
  canonicalHost: 'www.reddit.com',
  textPosition: 'above',
  matchesHost: (host) => host === 'reddit.com' || host.endsWith('.reddit.com') || host === 'redd.it',
  /** A single opaque segment is a `redd.it` share code — the rewrite rule
   *  drops the host, so `redd.it/abc123` arrives as just `abc123`. */
  buildOriginalUrl: (pathRest, search) => {
    const first = pathRest.split('/')[0] ?? '';
    if (first && !pathRest.includes('/') && !KNOWN_ROOTS.has(first)) {
      return `https://redd.it/${first}${search}`;
    }
    return `${HOST}/${pathRest}${search}`;
  },
  resolve,
};