// lib/metadata/metadata_normalizer.dart
import 'metadata_model.dart';

class MetadataNormalizer {
  NormalizedMetadata normalize(RawMetadata raw,
      {String fileName = '', String filePath = ''}) {
    final tagTitle = raw.title.trim();
    final tagArtist = raw.artist.trim();
    final tagAlbum = raw.album.trim();

    final finalTitle =
        tagTitle.isNotEmpty ? tagTitle : _inferTitleFromFileName(fileName);

    final artistFromPath = _inferArtistFromPath(filePath);
    final finalArtist = tagArtist.isNotEmpty
        ? tagArtist
        : (raw.performers.isNotEmpty ? raw.performers.first : artistFromPath);

    return NormalizedMetadata(
      title: finalTitle,
      artist: finalArtist,
      album: tagAlbum,
      genres: raw.genres,
      performers: raw.performers,
      year: raw.year,
      trackNumber: raw.trackNumber,
      trackTotal: raw.trackTotal,
      discNumber: raw.discNumber,
      totalDisc: raw.totalDisc,
      duration: raw.duration,
      artwork: raw.artwork,
      titleFromTag: tagTitle.isNotEmpty,
      artistFromTag: tagArtist.isNotEmpty || raw.performers.isNotEmpty,
      albumFromTag: tagAlbum.isNotEmpty,
    );
  }

  String _inferTitleFromFileName(String fileName) {
    final dotIndex = fileName.lastIndexOf('.');
    return dotIndex > 0
        ? fileName.substring(0, dotIndex).trim()
        : fileName.trim();
  }

  String _inferArtistFromPath(String filePath) {
    final parts = filePath.split(RegExp(r'[/\\]'));
    if (parts.length >= 2) {
      final candidate = parts[parts.length - 2].trim();
      if (candidate.isNotEmpty && !candidate.startsWith('http')) {
        return candidate;
      }
    }
    return '未知艺术家';
  }

  /// 置信度评估（元数据引擎第 2 步）。
  ///
  /// 设计原则：
  ///   1. 标签 >= 推断：来自标签的字段永远比文件名/目录推断更可信；
  ///   2. 字段齐全度：标题、艺术家、专辑依次加分；
  ///   3. 历史一致性：同一艺人/专辑已有多条可信记录时额外加权，
  ///      这是"自学习"的入口——库越大，判断越稳；
  ///   4. 可解释：每个加分项都写进 evidence，方便日志与后续调参。
  ///
  /// 分数区间大致：
  ///   0.35  只有文件名
  ///   0.55  标题来自标签、艺术家靠推断
  ///   0.80  标题 + 艺术家都来自标签
  ///   0.90  标题 + 艺术家 + 专辑
  ///   0.95  以上再加年份/封面/历史一致性
  CandidateMetadata evaluate(
      NormalizedMetadata normalized, List<Map<String, dynamic>> history) {
    final evidence = <String, double>{};
    var confidence = 0.25;
    evidence['base'] = 0.25;

    if (normalized.title.isNotEmpty) {
      confidence += 0.20;
      evidence['title'] = 0.20;
    }
    if (normalized.titleFromTag) {
      confidence += 0.10;
      evidence['title_from_tag'] = 0.10;
    } else if (normalized.title.isNotEmpty) {
      // 拿文件名当标题：明确扣分
      confidence -= 0.10;
      evidence['title_inferred_penalty'] = -0.10;
    }

    if (normalized.artist.isNotEmpty && normalized.artist != '未知艺术家') {
      confidence += 0.15;
      evidence['artist'] = 0.15;
    }
    if (normalized.artistFromTag) {
      confidence += 0.10;
      evidence['artist_from_tag'] = 0.10;
    }

    if (normalized.album.isNotEmpty) {
      confidence += 0.10;
      evidence['album'] = 0.10;
    }
    if (normalized.year > 0) {
      confidence += 0.03;
      evidence['year'] = 0.03;
    }
    if (normalized.artwork != null && normalized.artwork!.isNotEmpty) {
      confidence += 0.02;
      evidence['artwork'] = 0.02;
    }

    // ---- 历史一致性（自学习的核心）----
    if (history.isNotEmpty) {
      final sameArtist = history
          .where((row) => (row['artist'] as String?) == normalized.artist)
          .length;
      if (sameArtist >= 2) {
        confidence += 0.05;
        evidence['artist_history'] = 0.05;
      }

      if (normalized.album.isNotEmpty) {
        final sameAlbum = history
            .where((row) => (row['album'] as String?) == normalized.album)
            .length;
        if (sameAlbum >= 2) {
          confidence += 0.03;
          evidence['album_history'] = 0.03;
        }
      }
    }

    confidence = confidence.clamp(0.05, 0.98);
    return CandidateMetadata(
      metadata: normalized,
      confidence: double.parse(confidence.toStringAsFixed(2)),
      evidence: evidence,
    );
  }

  /// 按阈值决定最终元数据。
  /// 低于阈值时仍返回数据（用于展示），但 source 标成 pending，
  /// 调用方据此累计 validation_count、下次播放重新确认。
  FinalMetadata decide(CandidateMetadata candidate, {double threshold = 0.6}) {
    return FinalMetadata(
      title: candidate.metadata.title,
      artist: candidate.metadata.artist,
      album: candidate.metadata.album,
      genre: candidate.metadata.genres.isNotEmpty
          ? candidate.metadata.genres.first
          : '',
      genres: candidate.metadata.genres,
      performers: candidate.metadata.performers,
      year: candidate.metadata.year,
      trackNumber: candidate.metadata.trackNumber,
      trackTotal: candidate.metadata.trackTotal,
      discNumber: candidate.metadata.discNumber,
      totalDisc: candidate.metadata.totalDisc,
      duration: candidate.metadata.duration,
      artwork: candidate.metadata.artwork,
      source: candidate.confidence >= threshold ? 'normalized' : 'pending',
    );
  }
}