mathtool2/lib/expr_editor.dart

import 'package:flutter/material.dart';

import 'expr_node.dart';

/// 结构化表达式的 2D 编辑器视图。
///
/// 渲染方式：直接把节点树翻译成 widget 树 —— 分式用 Column（分子/横线/分母）、
/// 幂用 Row + 抬高的上标、函数用 `名字[ 参数 ]`。没有自己写排版引擎，
/// 因为 Flutter 的布局本来就够用，而且这样点击命中、无障碍都能白拿。
class ExprEditor extends StatelessWidget {
  const ExprEditor({
    super.key,
    required this.doc,
    required this.onChanged,
    this.fontSize = 22,
  });

  final ExprDoc doc;

  /// 光标或内容变化后调用，让页面刷新。
  final VoidCallback onChanged;

  final double fontSize;

  void _setCursor(BuildContext context, SlotPath p) {
    if (doc.cursor == p) return;
    doc.cursor = p;
    onChanged();
  }

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      scrollDirection: Axis.horizontal,
      reverse: true, // 长表达式总是把光标一侧露出来
      child: ConstrainedBox(
        constraints: BoxConstraints(
          minWidth: MediaQuery.sizeOf(context).width - 32,
        ),
        child: Align(
          alignment: Alignment.centerRight,
          child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
            child: _SlotView(
              doc: doc,
              seq: doc.root,
              path: SlotPath.root,
              size: fontSize,
              onCursor: (p) => _setCursor(context, p),
            ),
          ),
        ),
      ),
    );
  }
}

/// 一个槽的视图：把孩子按顺序排开，在光标位置插一根竖线。
class _SlotView extends StatelessWidget {
  const _SlotView({
    required this.doc,
    required this.seq,
    required this.path,
    required this.size,
    required this.onCursor,
  });

  final ExprDoc doc;
  final SeqNode seq;
  final SlotPath path;
  final double size;
  final void Function(SlotPath) onCursor;

  @override
  Widget build(BuildContext context) {
    final scheme = Theme.of(context).colorScheme;
    // 用 sameSlotAs 而不是 ==：offset 是槽内的插入位置，不属于槽的身份
    final focused = doc.cursor.sameSlotAs(path);

    return GestureDetector(
      // 点槽的空白处 → 光标落到槽尾
      onTap: () => onCursor(SlotPath(path.steps, seq.children.length)),
      behavior: HitTestBehavior.opaque,
      child: Container(
        padding: const EdgeInsets.symmetric(horizontal: 2, vertical: 3),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(4),
          color: focused ? scheme.primary.withValues(alpha: 0.06) : null,
        ),
        child: Wrap(
          crossAxisAlignment: WrapCrossAlignment.center,
          children: [
            for (var i = 0; i < seq.children.length; i++) ...[
              if (focused && doc.cursor.offset == i) _caret(scheme),
              _NodeView(
                doc: doc,
                node: seq.children[i],
                parent: path,
                index: i,
                size: size,
                onCursor: onCursor,
              ),
            ],
            if (focused && doc.cursor.offset >= seq.children.length)
              _caret(scheme),
            // 空槽给个占位，否则用户不知道能往里点
            if (seq.isEmpty && !focused) _placeholder(scheme),
          ],
        ),
      ),
    );
  }

  /// 光标。**常亮、不闪烁**。
  ///
  /// 之前做成 0.15~1.0 的平滑呼吸，最暗那半程看着就跟没有一样（用户反馈
  /// "有时能看到有时看不到"）。计算器不是文本编辑器，聚焦的槽本来就有底色
  /// 高亮，这里再常亮一根实心竖线，位置一眼就能看到。
  Widget _caret(ColorScheme scheme) => Container(
        // 整个编辑区同时最多只有一根光标，所以固定 key 不会冲突。
        // 加它是为了能写"打完字光标还在不在"的回归测试 —— 这个 bug
        // 之前就是靠人眼看截图才发现的。
        key: const ValueKey('expr-caret'),
        width: 2.5,
        height: size * 1.25,
        margin: const EdgeInsets.symmetric(horizontal: 1),
        color: scheme.primary,
      );

  Widget _placeholder(ColorScheme scheme) => Container(
        width: 12,
        height: size * 1.05,
        margin: const EdgeInsets.symmetric(horizontal: 1),
        decoration: BoxDecoration(
          border: Border.all(color: scheme.outlineVariant, width: 1),
          borderRadius: BorderRadius.circular(2),
        ),
      );
}

/// 单个节点的视图。
class _NodeView extends StatelessWidget {
  const _NodeView({
    required this.doc,
    required this.node,
    required this.parent,
    required this.index,
    required this.size,
    required this.onCursor,
  });

  final ExprDoc doc;
  final ExprNode node;

  /// 该节点所在槽的路径，以及它在槽里的下标。
  final SlotPath parent;
  final int index;

  final double size;
  final void Function(SlotPath) onCursor;

  @override
  Widget build(BuildContext context) {
    final scheme = Theme.of(context).colorScheme;
    // 点中某个节点 → 光标落到它后面（符合"接着往下打"的直觉）
    return GestureDetector(
      onTap: () => onCursor(SlotPath(parent.steps, index + 1)),
      behavior: HitTestBehavior.opaque,
      child: switch (node) {
        LitNode l => _literal(l, scheme),
        FuncNode f => _function(context, f),
        FracNode f => _fraction(context, f),
        PowNode p => _power(context, p),
        GroupNode g => _group(context, g),
        PostfixNode p => _row([
            _slot(context, p.operand, parent.push(index, 0)),
            _text(p.op, size),
          ]),
      },
    );
  }

  Widget _literal(LitNode l, ColorScheme scheme) {
    final isLetter = RegExp(r'^[A-Za-z]+$').hasMatch(l.text);
    return Text(
      l.text,
      style: TextStyle(
        fontSize: size,
        fontFamily: 'serif',
        fontStyle: isLetter ? FontStyle.italic : FontStyle.normal,
        color: scheme.onSurface,
      ),
    );
  }

  Widget _function(BuildContext context, FuncNode f) {
    final scheme = Theme.of(context).colorScheme;
    return _row([
      Text(
        f.name,
        style: TextStyle(fontSize: size * 0.85, color: scheme.primary),
      ),
      Text('[', style: TextStyle(fontSize: size, color: scheme.onSurface)),
      for (var i = 0; i < f.args.length; i++) ...[
        if (i > 0)
          Text(', ', style: TextStyle(fontSize: size, color: scheme.onSurface)),
        _slot(context, f.args[i], parent.push(index, i)),
      ],
      Text(']', style: TextStyle(fontSize: size, color: scheme.onSurface)),
    ]);
  }

  Widget _fraction(BuildContext context, FracNode f) {
    final scheme = Theme.of(context).colorScheme;
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 2),
      // IntrinsicWidth 让横线刚好横跨分子分母里较宽的那个。
      // 不能直接 width: double.infinity —— 这里是 Wrap 里的无界宽度，会报错。
      child: IntrinsicWidth(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            _slot(context, f.num, parent.push(index, 0)),
            Container(height: 1.4, color: scheme.onSurface),
            _slot(context, f.den, parent.push(index, 1)),
          ],
        ),
      ),
    );
  }

  Widget _power(BuildContext context, PowNode p) {
    return _row([
      _slot(context, p.base, parent.push(index, 0)),
      Transform.translate(
        offset: Offset(0, -size * 0.35),
        child: _slot(context, p.exp, parent.push(index, 1), scale: 0.7),
      ),
    ]);
  }

  Widget _group(BuildContext context, GroupNode g) {
    final scheme = Theme.of(context).colorScheme;
    final style = TextStyle(fontSize: size, color: scheme.onSurface);
    return _row([
      Text('(', style: style),
      _slot(context, g.inner, parent.push(index, 0)),
      Text(')', style: style),
    ]);
  }

  Widget _row(List<Widget> children) => Wrap(
        crossAxisAlignment: WrapCrossAlignment.center,
        children: children,
      );

  Widget _slot(BuildContext context, SeqNode seq, SlotPath path,
          {double scale = 1}) =>
      _ScaledSlot(
        scale: scale,
        child: _SlotView(
          doc: doc,
          seq: seq,
          path: path,
          size: size,
          onCursor: onCursor,
        ),
      );

  Widget _text(String t, double s) => Text(t, style: TextStyle(fontSize: s));
}

/// 给槽套一个缩放（指数要用小一号字）。
class _ScaledSlot extends StatelessWidget {
  const _ScaledSlot({required this.scale, required this.child});

  final double scale;
  final Widget child;

  @override
  Widget build(BuildContext context) {
    if (scale == 1) return child;
    // 用 Transform 缩放而不是改字号：字号变了槽的布局参数也得跟着变，
    // 缩放一行搞定且视觉上等价。
    return Transform.scale(
      scale: scale,
      alignment: Alignment.bottomLeft,
      child: child,
    );
  }
}