import 'dart:math' as math;

import 'detection_result.dart';

/// 帧差运动聚合：每像素 0/1 差分掩码 → 8x8 分块统计 → 连通块聚合为运动区域。
class MotionAggregator {
  static const int blockGrid = 8;
  static const double blockActiveRatio = 0.30;
  static const int maxRegions = 3;
  static const int diffThreshold = 25;

  static List<MotionRegion> aggregate(List<int> diff, int width, int height) {
    final bw = width ~/ blockGrid;
    final bh = height ~/ blockGrid;
    if (bw == 0 || bh == 0) return const [];

    final active = List<bool>.filled(blockGrid * blockGrid, false);
    for (var by = 0; by < blockGrid; by++) {
      for (var bx = 0; bx < blockGrid; bx++) {
        final blockW = bx == blockGrid - 1 ? width - bx * bw : bw;
        final blockH = by == blockGrid - 1 ? height - by * bh : bh;
        var motion = 0;
        for (var y = by * bh; y < by * bh + blockH; y++) {
          var idx = y * width + bx * bw;
          for (var x = 0; x < blockW; x++) {
            motion += diff[idx + x];
          }
          idx += width;
        }
        active[by * blockGrid + bx] =
            motion > blockW * blockH * blockActiveRatio;
      }
    }

    final regions = <MotionRegion>[];
    final visited = List<bool>.filled(active.length, false);
    for (var i = 0; i < active.length; i++) {
      if (!active[i] || visited[i]) continue;
      var minX = blockGrid, minY = blockGrid, maxX = -1, maxY = -1;
      final stack = <int>[i];
      visited[i] = true;
      while (stack.isNotEmpty) {
        final cur = stack.removeLast();
        final bx = cur % blockGrid;
        final by = cur ~/ blockGrid;
        if (bx < minX) minX = bx;
        if (bx > maxX) maxX = bx;
        if (by < minY) minY = by;
        if (by > maxY) maxY = by;
        for (final nb in neighbors(cur)) {
          if (active[nb] && !visited[nb]) {
            visited[nb] = true;
            stack.add(nb);
          }
        }
      }
      if (maxX - minX > 3 || maxY - minY > 3) continue; // 全屏噪声过滤
      regions.add(MotionRegion(
        minX * bw / width,
        minY * bh / height,
        math.min((maxX + 1) * bw, width) / width,
        math.min((maxY + 1) * bh, height) / height,
      ));
      if (regions.length >= maxRegions) break;
    }
    return regions;
  }

  static List<int> neighbors(int i) {
    final bx = i % blockGrid;
    final by = i ~/ blockGrid;
    final list = <int>[];
    if (bx > 0) list.add(i - 1);
    if (bx < blockGrid - 1) list.add(i + 1);
    if (by > 0) list.add(i - blockGrid);
    if (by < blockGrid - 1) list.add(i + blockGrid);
    return list;
  }

  /// 检测框中心是否落在运动区域内（用于置信度提升判定）
  static bool centerInRegion(DetectionResult box, MotionRegion region) =>
      box.centerX >= region.left &&
      box.centerX <= region.right &&
      box.centerY >= region.top &&
      box.centerY <= region.bottom;

  /// 帧差掩码：|g - prev| > threshold → 1
  static List<int> diffMask(List<int> gray, List<int> prev,
      [int threshold = diffThreshold]) {
    final diff = List<int>.filled(gray.length, 0);
    for (var i = 0; i < gray.length; i++) {
      diff[i] = (gray[i] - prev[i]).abs() > threshold ? 1 : 0;
    }
    return diff;
  }
}