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

/// 状态机判定结果
class StabilityDecision {
  /// 'verified' | 'pending'
  final String status;
  final String reason;
  final int validationCount;

  const StabilityDecision({
    required this.status,
    required this.reason,
    required this.validationCount,
  });

  bool get isVerified => status == 'verified';
}

/// 元数据状态机：决定一条记录能不能升级为 verified。
///
/// 第 2 步的规则是"置信度 >= 0.6 且验证次数 >= 2"，太粗暴：
/// 两次读到的是不同结果也会被当成"验证通过"。这里加入一致性检查——
///
///   - 首次见到 → pending（需要第二次确认）
///   - 与上次记录冲突（标题或艺术家明显不同）→ 次数重置为 1，继续 pending
///   - 一致且次数 >= 2、置信度达标 → verified
///   - 置信度不足 → pending
///
/// 这样一次误读不会把错误标签固化，下次播放会重新校正。
class MetadataStability {
  static const double threshold = 0.6;

  static StabilityDecision decide({
    required Map<String, dynamic>? previous,
    required CandidateMetadata candidate,
    required String title,
    required String artist,
  }) {
    if (previous == null) {
      return const StabilityDecision(
        status: 'pending',
        reason: 'first_seen',
        validationCount: 1,
      );
    }

    final prevConfidence =
        (previous['confidence'] as num?)?.toDouble() ?? 0.0;
    final prevTitle = previous['title'] as String? ?? '';
    final prevArtist = previous['artist'] as String? ?? '';
    final prevCount = (previous['validation_count'] as int?) ?? 0;

    final consistent = _similar(prevTitle, title) && _similar(prevArtist, artist);
    if (!consistent) {
      return const StabilityDecision(
        status: 'pending',
        reason: 'conflict',
        validationCount: 1,
      );
    }

    final count = prevCount + 1;
    final best = candidate.confidence > prevConfidence
        ? candidate.confidence
        : prevConfidence;

    if (best < threshold) {
      return StabilityDecision(
        status: 'pending',
        reason: 'low_confidence',
        validationCount: count,
      );
    }

    if (count < 2) {
      return StabilityDecision(
        status: 'pending',
        reason: 'need_second_validation',
        validationCount: count,
      );
    }

    return StabilityDecision(
      status: 'verified',
      reason: 'stable',
      validationCount: count,
    );
  }

  /// 字段缺失不算冲突；只有两边都有值且不同才算。
  static bool _similar(String a, String b) {
    final left = a.trim().toLowerCase();
    final right = b.trim().toLowerCase();
    if (left.isEmpty || right.isEmpty) return true;
    return left == right;
  }
}