ReelShort/lib/pages/player/widgets/expandable_synopsis.dart

// Author: fruit.com.cn
// 职责：推荐流与播放页共用的简介样式、固定切换入口与高度过渡。
import 'package:flutter/material.dart';

import '../../../core/theme/app_colors.dart';
import '../../../l10n/app_localizations.dart';

const double _synopsisFont = 15;
const double _synopsisLineHeight = 1.4;
const int _collapsedSynopsisLines = 2;
const double _synopsisToggleWidthFraction = 0.55;
const double _synopsisToggleGap = 6;
const _synopsisMotion = Duration(milliseconds: 240);
const _synopsisStyle = TextStyle(
  fontSize: _synopsisFont,
  fontWeight: FontWeight.w400,
  height: _synopsisLineHeight,
);
const _synopsisToggleStyle = TextStyle(
  color: AppColors.textPrimary,
  fontSize: _synopsisFont,
  fontWeight: FontWeight.w400,
  height: _synopsisLineHeight,
);

/// 两行折叠的简介，展开与收起入口在右下共用同一占位。
class ExpandableSynopsis extends StatefulWidget {
  /// [keyPrefix] 区分页内标识，[expandedFooter] 仅在展开时展示。
  const ExpandableSynopsis({
    super.key,
    required this.synopsis,
    this.keyPrefix = 'home-feed',
    this.expandedFooter,
    this.textColor = AppColors.homeFeedVideoCopy,
  });

  /// 按当前语言获取的简介正文。
  final String synopsis;

  /// 当前页面的组件标识前缀。
  final String keyPrefix;

  /// 展开后附加的声明等内容。
  final Widget? expandedFooter;

  /// 简介正文颜色；默认使用视频信息区统一的半透明浅灰白。
  final Color textColor;

  @override
  State<ExpandableSynopsis> createState() => _ExpandableSynopsisState();
}

class _ExpandableSynopsisState extends State<ExpandableSynopsis> {
  bool _expanded = false;

  @override
  void didUpdateWidget(covariant ExpandableSynopsis oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.synopsis != widget.synopsis) _expanded = false;
  }

  @override
  Widget build(BuildContext context) {
    if (widget.synopsis.trim().isEmpty) return const SizedBox.shrink();
    final l10n = AppLocalizations.of(context)!;
    return LayoutBuilder(
      builder: (context, constraints) {
        if (!_needsToggle(constraints.maxWidth)) return _body();
        return Row(
          key: _key('layout'),
          crossAxisAlignment: CrossAxisAlignment.end,
          children: [
            Expanded(
              child: GestureDetector(
                behavior: HitTestBehavior.opaque,
                onTap: _toggle,
                child: _animatedBody(),
              ),
            ),
            const SizedBox(width: _synopsisToggleGap),
            ConstrainedBox(
              constraints: BoxConstraints(
                maxWidth: constraints.maxWidth * _synopsisToggleWidthFraction,
              ),
              child: IntrinsicWidth(child: _toggleButton(l10n)),
            ),
          ],
        );
      },
    );
  }

  bool _needsToggle(double maxWidth) {
    final painter = _painter(widget.synopsis, _bodyStyle);
    painter.layout(maxWidth: maxWidth);
    final overflows = painter.didExceedMaxLines;
    painter.dispose();
    return overflows;
  }

  TextPainter _painter(String text, TextStyle style) => TextPainter(
    text: TextSpan(
      text: text,
      style: DefaultTextStyle.of(context).style.merge(style),
    ),
    maxLines: _collapsedSynopsisLines,
    textDirection: Directionality.of(context),
    textScaler: MediaQuery.textScalerOf(context),
    locale: Localizations.localeOf(context),
    textHeightBehavior: DefaultTextStyle.of(context).textHeightBehavior,
  );

  Widget _animatedBody() {
    if (MediaQuery.disableAnimationsOf(context)) return _body();
    return AnimatedSize(
      key: _key('size'),
      duration: _synopsisMotion,
      curve: Curves.easeInOutCubic,
      alignment: Alignment.topLeft,
      child: _body(),
    );
  }

  Key _key(String suffix) => Key('${widget.keyPrefix}-synopsis-$suffix');

  TextStyle get _bodyStyle => _synopsisStyle.copyWith(color: widget.textColor);

  Widget _body() {
    final style = _bodyStyle;
    final text = Text.rich(
      TextSpan(text: widget.synopsis, style: style),
      key: _expanded ? _key('expanded') : Key('${widget.keyPrefix}-synopsis'),
      style: style,
      maxLines: _expanded ? null : _collapsedSynopsisLines,
      overflow: _expanded ? TextOverflow.clip : TextOverflow.ellipsis,
    );
    if (!_expanded || widget.expandedFooter == null) return text;
    return Column(
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [text, widget.expandedFooter!],
    );
  }

  Widget _toggleButton(AppLocalizations l10n) => Semantics(
    button: true,
    expanded: _expanded,
    child: GestureDetector(
      key: _key('more'),
      behavior: HitTestBehavior.opaque,
      onTap: _toggle,
      child: IndexedStack(
        index: _expanded ? 1 : 0,
        alignment: Alignment.bottomRight,
        children: [
          _toggleLabel(l10n.expandSynopsis),
          _toggleLabel(l10n.showLess),
        ],
      ),
    ),
  );

  Widget _toggleLabel(String label) => Text(
    label,
    maxLines: _collapsedSynopsisLines,
    overflow: TextOverflow.ellipsis,
    textAlign: TextAlign.right,
    style: _synopsisToggleStyle,
  );

  void _toggle() => setState(() => _expanded = !_expanded);
}