import type { Cue } from "./vtt";

// yt-dlp writes live_chat as JSON-lines (one continuation action per line),
// extracted from YouTube's youtube_live_chat_replay protocol. Each line wraps
// a `replayChatItemAction` whose `actions[]` contain `addChatItemAction.item`
// entries with one of several renderers (`liveChatTextMessageRenderer`,
// `liveChatPaidMessageRenderer`, `liveChatMembershipItemRenderer`, etc.).
//
// We emit one Cue per addChatItemAction that has a renderable text body, with
// `start` derived from `videoOffsetTimeMsec` and `text` formatted as
// `<author>: <message>`. Non-text events (ticker pings without an associated
// message, viewer-engagement nags) are skipped.

type Run = { text?: string; emoji?: { emojiId?: string; shortcuts?: string[] } };
type MessageBody = { simpleText?: string; runs?: Run[] };
type AuthorBody = { simpleText?: string };
type ChatRenderer = {
  message?: MessageBody;
  headerSubtext?: MessageBody;
  text?: MessageBody;
  authorName?: AuthorBody;
};
type ChatItem = Record<string, ChatRenderer | undefined>;
type AddAction = { item?: ChatItem };
type ChatAction = { addChatItemAction?: AddAction };
type ReplayAction = {
  actions?: ChatAction[];
  videoOffsetTimeMsec?: string;
};
type ReplayEnvelope = {
  replayChatItemAction?: ReplayAction;
  videoOffsetTimeMsec?: string;
};

const TEXT_RENDERERS = [
  "liveChatTextMessageRenderer",
  "liveChatPaidMessageRenderer",
  "liveChatPaidStickerRenderer",
  "liveChatMembershipItemRenderer",
  "liveChatSponsorshipsGiftPurchaseAnnouncementRenderer",
  "liveChatSponsorshipsGiftRedemptionAnnouncementRenderer",
];

function renderMessage(body: MessageBody | undefined): string {
  if (!body) return "";
  if (typeof body.simpleText === "string") return body.simpleText;
  if (!Array.isArray(body.runs)) return "";
  const parts: string[] = [];
  for (const run of body.runs) {
    if (typeof run.text === "string") {
      parts.push(run.text);
    } else if (run.emoji?.shortcuts?.length) {
      parts.push(run.emoji.shortcuts[0]);
    }
  }
  return parts.join("");
}

function authorOf(renderer: ChatRenderer): string {
  return renderer.authorName?.simpleText ?? "";
}

function textOf(renderer: ChatRenderer): string {
  // Sponsorship gift announcements use `headerSubtext`; sticker/paid use
  // `message`; membership pings use `headerSubtext` too. Fall back through
  // the known fields.
  return (
    renderMessage(renderer.message) ||
    renderMessage(renderer.headerSubtext) ||
    renderMessage(renderer.text)
  );
}

export function parseLiveChat(src: string): Cue[] {
  const lines = src.split("\n");
  const cues: Cue[] = [];
  for (const line of lines) {
    const trimmed = line.trim();
    if (!trimmed) continue;
    let envelope: ReplayEnvelope;
    try {
      envelope = JSON.parse(trimmed) as ReplayEnvelope;
    } catch {
      continue;
    }
    const replay = envelope.replayChatItemAction;
    const offsetRaw =
      replay?.videoOffsetTimeMsec ?? envelope.videoOffsetTimeMsec;
    const offsetMs = offsetRaw ? Number(offsetRaw) : NaN;
    if (!Number.isFinite(offsetMs)) continue;
    const start = offsetMs / 1000;
    for (const action of replay?.actions ?? []) {
      const item = action.addChatItemAction?.item;
      if (!item) continue;
      for (const rendererKey of TEXT_RENDERERS) {
        const renderer = item[rendererKey];
        if (!renderer) continue;
        const text = textOf(renderer).trim();
        if (!text) continue;
        const author = authorOf(renderer);
        cues.push({
          start,
          end: start + 5,
          text: author ? `${author}: ${text}` : text,
        });
        break;
      }
    }
  }
  cues.sort((a, b) => a.start - b.start);
  return cues;
}