import { Innertube } from 'youtubei.js';
import { AppError } from '../../utils/errors.js';
import { canonicalSourceUrl, extractYouTubeId } from '../../utils/url.js';

function textValue(value) {
  if (value == null) return '';
  return typeof value === 'string' ? value : value.toString();
}

export function readTranscriptSegments(transcriptInfo) {
  const segments = transcriptInfo?.transcript?.content?.body?.initial_segments ?? [];
  return segments
    .filter((segment) => segment?.snippet && segment?.start_ms != null)
    .map((segment) => ({
      startSec: Number(segment.start_ms) / 1000,
      endSec: Number(segment.end_ms) / 1000,
      text: textValue(segment.snippet).trim(),
    }))
    .filter((segment) => Number.isFinite(segment.startSec) && segment.text);
}

export class YouTubeExtractor {
  constructor({ clientFactory } = {}) {
    this.clientFactory = clientFactory ?? (() => Innertube.create({
      lang: 'ko',
      location: 'KR',
      retrieve_player: false,
    }));
  }

  async extract(sourceUrl) {
    const sourceId = extractYouTubeId(sourceUrl);
    let info;

    try {
      const client = await this.clientFactory();
      info = await client.getInfo(sourceId);
    } catch (error) {
      throw new AppError('YouTube 정보를 가져오지 못했습니다.', {
        statusCode: 502,
        code: 'YOUTUBE_EXTRACTION_FAILED',
        cause: error,
      });
    }

    const basic = info.basic_info ?? {};
    const description = basic.short_description?.trim() ?? '';
    let transcriptSegments = [];

    try {
      transcriptSegments = readTranscriptSegments(await info.getTranscript());
    } catch {
      // 자막이 비활성화된 영상은 설명만으로 계속 분석한다.
    }

    if (!description && transcriptSegments.length === 0) {
      throw new AppError('YouTube 자막과 설명을 찾을 수 없습니다.', {
        statusCode: 422,
        code: 'YOUTUBE_TEXT_NOT_FOUND',
      });
    }

    const transcriptText = transcriptSegments
      .map((segment) => `[${segment.startSec}] ${segment.text}`)
      .join('\n');
    const rawText = [
      description && `[DESCRIPTION]\n${description}`,
      transcriptText && `[TRANSCRIPT]\n${transcriptText}`,
    ].filter(Boolean).join('\n\n');
    const thumbnails = basic.thumbnail ?? [];
    const thumbnail = thumbnails.length > 0 ? thumbnails[thumbnails.length - 1] : null;

    return {
      platform: 'youtube',
      sourceUrl: canonicalSourceUrl(sourceUrl),
      sourceId,
      title: basic.title?.trim() || null,
      author: basic.author?.trim() || basic.channel?.name?.trim() || null,
      thumbnailUrl: thumbnail?.url ?? null,
      rawText,
      metadata: {
        durationSec: basic.duration ?? null,
        transcript: transcriptSegments,
      },
    };
  }
}