// Author: fruit.com.cn
// 职责：协调首页三页的点击动画、最终选中目标和手势中断。
import 'package:flutter/widgets.dart';

const _transitionDuration = Duration(milliseconds: 220);

/// 页面移动时保留用户最终目标，防止跨页动画途中的页面抢占高亮。
class HomeTabMotionController extends PageController {
  /// [onSettled] 在动画结束或被手势中断时同步实际停留页面。
  HomeTabMotionController({required this.onSettled});

  final ValueChanged<int> onSettled;
  int? _target;
  int _revision = 0;
  bool _disposed = false;

  /// 供导航绘制连续位置；布局尚未建立时使用初始页。
  double get pagePosition => hasClients && position.hasContentDimensions
      ? page ?? initialPage.toDouble()
      : initialPage.toDouble();

  /// 点击跨页过程中只接受最终目标；拖动和稳定状态接受实际页。
  bool acceptsSelection(int index) => _target == null || _target == index;

  /// 点击导航时平滑移动；系统减少动画时直接到位。
  Future<void> selectPage(int index, {required bool reduceMotion}) async {
    final revision = ++_revision;
    _target = index;
    if (!hasClients) {
      _target = null;
      return;
    }
    if (reduceMotion) {
      jumpToPage(index);
    } else {
      await animateToPage(
        index,
        duration: _transitionDuration,
        curve: Curves.easeOut,
      );
    }
    if (_disposed || revision != _revision) return;
    _target = null;
    if (hasClients) onSettled(pagePosition.round());
  }

  @override
  void dispose() {
    _disposed = true;
    super.dispose();
  }
}