import 'dart:typed_data';

import '../detection/detection_result.dart';
import '../detection/motion_aggregator.dart';

/// 轻量运动检测：相邻帧 Y 通道差分 + 分块聚合。
/// 小尺寸工作（约 128x128 内），在分析流中串行调用。
/// 相机大幅移动时（全屏帧差）自动忽略本帧，避免误报。
class MotionDetector {
  final int maxWidth;
  final int maxHeight;

  List<int>? _prevGray;

  MotionDetector({this.maxWidth = 128, this.maxHeight = 128});

  /// 后台 isolate 用原始数据接口（不依赖 CameraImage）。
  List<MotionRegion> detectMotionRaw(
      Uint8List yPlane, int yStride, int width, int height) {
    final w = width, h = height;
    final scale = maxWidth / w < maxHeight / h ? maxWidth / w : maxHeight / h;
    final tw = (w * scale).toInt().clamp(1, maxWidth);
    final th = (h * scale).toInt().clamp(1, maxHeight);
    if (tw == 0 || th == 0) return const [];

    // 取 Y 平面缩放灰度（最近邻下采样到 128x128 内）
    final y = yPlane;
    final gray = List<int>.filled(tw * th, 0);
    for (var oy = 0; oy < th; oy++) {
      final sy = (oy / scale).toInt().clamp(0, h - 1);
      for (var ox = 0; ox < tw; ox++) {
        final sx = (ox / scale).toInt().clamp(0, w - 1);
        gray[oy * tw + ox] = y[sy * yStride + sx];
      }
    }

    final prev = _prevGray;
    _prevGray = List.of(gray);
    if (prev == null || prev.length != gray.length) return const [];

    final diff = MotionAggregator.diffMask(gray, prev);
    final motionTotal = diff.fold(0, (a, b) => a + b);
    // 全屏大差异 → 相机移动/大范围变化，忽略本帧
    if (motionTotal > tw * th / 2) return const [];
    if (motionTotal < 12) return const [];
    return MotionAggregator.aggregate(diff, tw, th);
  }

  /// 相机切换后重置参考帧，避免旧帧误差
  void reset() {
    _prevGray = null;
  }
}