/** The platforms antisocial understands. */
export type PlatformId = 'x' | 'threads' | 'instagram' | 'tiktok' | 'bluesky' | 'reddit';

/**
 * Something fetchable that lives on someone else's CDN.
 *
 * Most of these get rewritten to a `/m/` proxy URL before they reach the
 * page, because Instagram and TikTok reject requests that arrive without the
 * right `Referer` and cookies, and because proxying keeps the viewer's
 * browser from talking to the platform at all.
 */
export type Asset = {
  url: string;
  /** Headers the upstream CDN insists on. Held server-side, never in the page. */
  fetchHeaders?: Record<string, string>;
  /** Point the page straight at the CDN instead of proxying. Used for HLS,
   *  where proxying would mean rewriting playlists and every segment. */
  direct?: boolean;
};

type MediaBase = Asset & {
  width?: number;
  height?: number;
};

export type Media =
  | (MediaBase & { kind: 'image'; alt?: string })
  | (MediaBase & {
      kind: 'video';
      poster?: Asset;
      durationSec?: number;
      /** An HLS playlist rather than a progressive file. Safari plays these
       *  natively; other browsers get a note. */
      hls?: boolean;
    });

export type Author = {
  handle: string;
  displayName?: string;
  avatar?: Asset;
};

/**
 * A post that the post being shown is talking about.
 *
 * Held apart from the segment quoting it rather than folded into it. The
 * words and the pictures belong to someone else, and showing them under the
 * quoter's name — which is what folding them in amounts to — tells the
 * reader something untrue about who said what.
 */
export type Quoted = {
  author: Author;
  text?: string;
  media: Media[];
  /** ISO 8601. */
  postedAt?: string;
  /** The quoted post's own URL, so it can be opened on its own. */
  url?: string;
};

/**
 * One post. Usually a whole `Post` is a single segment, but on the platforms
 * where people write in chains — Bluesky and Threads — the author's own
 * follow-ups belong with the one that was linked, and other people's replies
 * do not.
 */
export type Segment = {
  /** Only Reddit gives a post a headline of its own. Everywhere else the
   *  first words of the body do that job, so this is left unset. */
  title?: string;
  text?: string;
  media: Media[];
  /** ISO 8601. */
  postedAt?: string;
  /** The post this one quotes, where there is one. */
  quoted?: Quoted;
  /** The post the link actually pointed at. Only meaningful when a thread
   *  has more than one segment. */
  isAnchor?: boolean;
};

/**
 * One comment, with the replies that hang off it.
 *
 * A tree rather than a flat list with depths: collapsing a comment has to
 * take everything under it along, and nesting is what makes that free.
 */
export type Comment = {
  /** Already prefixed, e.g. `u/someone`. `[deleted]` is left as it came. */
  author: string;
  text?: string;
  /** ISO 8601. */
  postedAt?: string;
  /** Absent when the platform is still hiding it on a new comment. */
  score?: number;
  /** The author of the post, replying under it. */
  isAuthor?: boolean;
  /** Marked by the platform as a moderator or admin comment. */
  distinguished?: string;
  replies: Comment[];
  /** Replies that exist upstream but were not on the page we were given.
   *  Shown as a count, since following them means going to the platform. */
  moreReplies?: number;
};

/**
 * The single shape every adapter produces and the renderer consumes. Adding
 * a platform means producing one of these; nothing downstream changes.
 */
export type Post = {
  platform: PlatformId;
  /** Human label for the badge: "X", "Threads", ... */
  platformLabel: string;
  /** Canonical original URL, cleaned of tracking parameters. This is what
   *  the copy button hands back. */
  originalUrl: string;
  author: Author;
  /** Fixed per platform: the ones that lead with words put the text above
   *  the media, the ones that lead with pictures put it below. */
  textPosition: 'above' | 'below';
  /** In the order they were written. Never empty. */
  segments: Segment[];
  /**
   * The conversation under the post, where the platform has one worth
   * showing. Only Reddit fills this in: elsewhere the replies are strangers
   * arguing beneath something that was shared for its own sake, but on
   * Reddit the thread is usually the point of the link.
   */
  comments?: Comment[];
  /** Top-level comments the first page did not carry. */
  moreComments?: number;
  /** What the platform says the total is, which is larger than what we
   *  show whenever `moreComments` is set. */
  commentCount?: number;
};

/** Most platforms have no notion of a chain, so their adapters use this. */
export function oneSegment(segment: Segment): Segment[] {
  return [{ ...segment, isAnchor: true }];
}

/** The segment the link pointed at, or the first one. */
export function anchorOf(post: Post): Segment | undefined {
  return post.segments.find((s) => s.isAnchor) ?? post.segments[0];
}

/**
 * Thrown when a post cannot be resolved. Carries enough for the error card
 * to still be useful: which platform, and the link to hand back.
 */
export class ResolveError extends Error {
  readonly platform: PlatformId;
  readonly originalUrl: string;

  constructor(message: string, platform: PlatformId, originalUrl: string, options?: ErrorOptions) {
    super(message, options);
    this.name = 'ResolveError';
    this.platform = platform;
    this.originalUrl = originalUrl;
  }
}

/**
 * A platform answered with a human-verification puzzle rather than the post.
 *
 * The page showing it is parked and still open, so the viewer can be handed
 * the puzzle to solve. Solving it leaves the resulting cookie in the shared
 * browser context, which is what makes the retry work.
 */
export class ChallengeError extends ResolveError {
  readonly challengeId: string;

  constructor(challengeId: string, platform: PlatformId, originalUrl: string) {
    super('A verification puzzle is in the way.', platform, originalUrl);
    this.name = 'ChallengeError';
    this.challengeId = challengeId;
  }
}