mathtool2/lib/tools/parametric_plotter.dart

// tools/parametric_plotter.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

import '../curve_plot.dart';
import '../symja.dart';

/// 参数方程绘图：x = f(t), y = g(t)，用 Symja 采样后交给 [CurvePlot] 画。
///
/// 采样要点：Symja 的 `sample` 一次只能算一个表达式，所以 x(t) 和 y(t) 各调用
/// 一次，参数区间和点数完全一致，再把两个结果按下标配成 (x, y) 点。
class ParametricPlotterPage extends StatefulWidget {
  const ParametricPlotterPage({super.key});

  @override
  State<ParametricPlotterPage> createState() => _ParametricPlotterPageState();
}

class _ParametricPlotterPageState extends State<ParametricPlotterPage> {
  final TextEditingController _xCtrl = TextEditingController(text: 'cos(t)');
  final TextEditingController _yCtrl = TextEditingController(text: 'sin(t)');
  final TextEditingController _tMinCtrl = TextEditingController(text: '0');
  final TextEditingController _tMaxCtrl = TextEditingController(text: '6.3');
  final TextEditingController _stepCtrl = TextEditingController(text: '0.1');

  List<CurveSeries> _series = const <CurveSeries>[];
  String? _error;
  bool _busy = false;

  @override
  void initState() {
    super.initState();
    // 首帧后再绘制：context.read 需要 element 已经挂载到 Provider 之下。
    WidgetsBinding.instance.addPostFrameCallback((_) => _plot());
  }

  @override
  void dispose() {
    _xCtrl.dispose();
    _yCtrl.dispose();
    _tMinCtrl.dispose();
    _tMaxCtrl.dispose();
    _stepCtrl.dispose();
    super.dispose();
  }

  Future<void> _plot() async {
    if (_busy) return;

    final xRaw = _xCtrl.text.trim();
    final yRaw = _yCtrl.text.trim();
    if (xRaw.isEmpty || yRaw.isEmpty) {
      setState(() => _error = '请填写 x(t) 和 y(t) 表达式');
      return;
    }

    final tMin = double.tryParse(_tMinCtrl.text.trim());
    final tMax = double.tryParse(_tMaxCtrl.text.trim());
    final step = double.tryParse(_stepCtrl.text.trim());
    if (tMin == null || tMax == null || step == null) {
      setState(() => _error = '请输入有效的 t 范围与步长');
      return;
    }
    if (tMin >= tMax) {
      setState(() => _error = 't最小值必须小于t最大值');
      return;
    }
    if (step <= 0) {
      setState(() => _error = '步长必须大于0');
      return;
    }

    // Symja 的 sample 只接受「点数」，这里把用户给的步长换算成点数，
    // 保留步长输入的含义；再做上下限保护，避免点数过多拖垮求值。
    final count = ((tMax - tMin) / step).round() + 1;
    final n = count.clamp(2, 5000).toInt();

    final session = context.read<SymjaSession>();
    setState(() {
      _busy = true;
      _error = null;
    });

    List<CurveSeries> series = const <CurveSeries>[];
    try {
      // 同一个 t 区间、同一点数分别采样两条曲线——Symja 一次只能算一个表达式。
      final xs = await session.sample(
        xRaw,
        variable: 't',
        from: tMin,
        to: tMax,
        count: n,
      );
      final ys = await session.sample(
        yRaw,
        variable: 't',
        from: tMin,
        to: tMax,
        count: n,
      );
      if (!mounted) return;

      final m = xs.ys.length < ys.ys.length ? xs.ys.length : ys.ys.length;
      series = <CurveSeries>[
        CurveSeries(
          label: 'x=$xRaw, y=$yRaw',
          color: Colors.blue,
          // NaN（极点/无定义点）照传，CurvePlot 会当成断点抬笔。
          points: <Offset>[
            for (var i = 0; i < m; i++) Offset(xs.ys[i], ys.ys[i]),
          ],
        ),
      ];
    } on SymjaException catch (e) {
      if (!mounted) return;
      setState(() {
        _error = '$e';
        _busy = false;
      });
      return;
    }

    if (!mounted) return;
    setState(() {
      _series = series;
      _busy = false;
    });
  }

  void _applyPreset(String xExpr, String yExpr, String tMin, String tMax) {
    setState(() {
      _xCtrl.text = xExpr;
      _yCtrl.text = yExpr;
      _tMinCtrl.text = tMin;
      _tMaxCtrl.text = tMax;
      _stepCtrl.text = '0.1';
    });
    _plot();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('参数方程绘图', style: TextStyle(color: Colors.black)),
        backgroundColor: Colors.white,
        elevation: 1,
      ),
      body: SingleChildScrollView(
        child: Column(
          children: [
            _buildInputPanel(),
            _buildGraph(),
            _buildExamples(),
          ],
        ),
      ),
    );
  }

  Widget _buildInputPanel() {
    return Card(
      elevation: 4,
      margin: const EdgeInsets.all(16),
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            const Text(
              '参数方程设置',
              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
            ),
            const SizedBox(height: 16),
            _buildExprField(_xCtrl, 'x = f(t)', '例如: cos(t), t^2, Cos[t]'),
            const SizedBox(height: 12),
            _buildExprField(_yCtrl, 'y = g(t)', '例如: sin(t), t^3, Sin[t]'),
            const SizedBox(height: 16),
            Row(
              children: [
                Expanded(child: _buildNumberField(_tMinCtrl, 't最小值')),
                const SizedBox(width: 12),
                Expanded(child: _buildNumberField(_tMaxCtrl, 't最大值')),
                const SizedBox(width: 12),
                Expanded(child: _buildNumberField(_stepCtrl, '步长')),
              ],
            ),
            const SizedBox(height: 12),
            if (_error != null)
              Container(
                width: double.infinity,
                padding: const EdgeInsets.all(12),
                decoration: BoxDecoration(
                  color: Colors.red[50],
                  borderRadius: BorderRadius.circular(8),
                  border: Border.all(color: Colors.red),
                ),
                child: Text(_error!, style: const TextStyle(color: Colors.red)),
              ),
            const SizedBox(height: 16),
            ElevatedButton.icon(
              onPressed: _busy ? null : _plot,
              icon: _busy
                  ? const SizedBox(
                      width: 16,
                      height: 16,
                      child: CircularProgressIndicator(strokeWidth: 2),
                    )
                  : const Icon(Icons.show_chart),
              label: Text(_busy ? '绘制中…' : '绘制图像'),
              style: ElevatedButton.styleFrom(
                minimumSize: const Size(double.infinity, 50),
              ),
            ),
          ],
        ),
      ),
    );
  }

  /// 表达式输入框。内容原样交给 Symja 解析，这里不做任何转换。
  Widget _buildExprField(
    TextEditingController controller,
    String label,
    String hint,
  ) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        TextField(
          controller: controller,
          decoration: InputDecoration(
            labelText: label,
            hintText: hint,
            border: const OutlineInputBorder(),
          ),
        ),
      ],
    );
  }

  Widget _buildNumberField(TextEditingController controller, String label) {
    return TextField(
      controller: controller,
      decoration: InputDecoration(
        labelText: label,
        border: const OutlineInputBorder(),
      ),
      keyboardType: TextInputType.numberWithOptions(
        signed: true,
        decimal: true,
      ),
    );
  }

  Widget _buildGraph() {
    return Card(
      elevation: 4,
      margin: const EdgeInsets.all(16),
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            const Text(
              '参数方程图像',
              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
            ),
            const SizedBox(height: 16),
            // 用 AspectRatio 强制正方形，参数曲线的 x/y 比例才不会被拉伸。
            AspectRatio(
              aspectRatio: 1,
              child: Container(
                decoration: BoxDecoration(
                  border: Border.all(color: Colors.grey[300]!),
                  borderRadius: BorderRadius.circular(8),
                ),
                child: _busy
                    ? const Center(child: CircularProgressIndicator())
                    : (_series.isEmpty
                        ? const Center(
                            child: Text(
                              '暂无数据',
                              style: TextStyle(fontSize: 16, color: Colors.grey),
                            ),
                          )
                        // 参数方程常常是圆/椭圆/螺线，必须等比例
                        : CurvePlot(series: _series, equalAspect: true)),
              ),
            ),
            const SizedBox(height: 16),
            Text(
              '方程: x = ${_xCtrl.text}, y = ${_yCtrl.text}',
              style: TextStyle(fontSize: 14, color: Colors.grey[600]),
            ),
            Text(
              '参数范围: t ∈ [${_tMinCtrl.text}, ${_tMaxCtrl.text}], 步长: ${_stepCtrl.text}',
              style: TextStyle(fontSize: 14, color: Colors.grey[600]),
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildExamples() {
    return Card(
      elevation: 4,
      margin: const EdgeInsets.all(16),
      child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            const Text(
              '示例方程',
              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
            ),
            const SizedBox(height: 12),
            Wrap(
              spacing: 8,
              runSpacing: 8,
              children: [
                _buildExampleChip('椭圆', '2*cos(t)', 'sin(t)', '0', '6.3'),
                _buildExampleChip('螺旋线', 't*cos(t)', 't*sin(t)', '0', '12.6'),
                _buildExampleChip('抛物线', 't', 't^2', '-2', '2'),
                _buildExampleChip(
                  '心形线',
                  '2*cos(t)-cos(2*t)',
                  '2*sin(t)-sin(2*t)',
                  '0',
                  '6.3',
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildExampleChip(
    String title,
    String xExpr,
    String yExpr,
    String tMin,
    String tMax,
  ) {
    return ActionChip(
      label: Text(title),
      onPressed: () => _applyPreset(xExpr, yExpr, tMin, tMax),
      backgroundColor: Colors.blue[50],
    );
  }
}