mathtool/lib/tools/derivative_calculator.dart

// tools/derivative_calculator.dart
import 'package:flutter/material.dart';
import 'package:math_expressions/math_expressions.dart';

class DerivativeCalculatorPage extends StatefulWidget {
  @override
  _DerivativeCalculatorPageState createState() => _DerivativeCalculatorPageState();
}

class _DerivativeCalculatorPageState extends State<DerivativeCalculatorPage> {
  final TextEditingController _functionController = TextEditingController();
  final TextEditingController _pointController = TextEditingController();
  String _result = '';
  String _derivative = '';
  bool _showPointInput = false;

  @override
  void dispose() {
    _functionController.dispose();
    _pointController.dispose();
    super.dispose();
  }

  void _calculateDerivative() {
    final String functionText = _functionController.text.trim();

    if (functionText.isEmpty) {
      setState(() {
        _result = '请输入函数表达式';
      _derivative = '';
      });
      return;
    }

    try {
      // 解析函数表达式
      Parser p = Parser();
      Expression exp = p.parse(functionText);

      // 对x求导
      Expression deriv = exp.derive('x');

      // 简化导数表达式
      Expression simplifiedDeriv = deriv.simplify();

      setState(() {
        _derivative = '导函数: ${simplifiedDeriv.toString()}';

      // 如果用户要求计算某点的导数值
      if (_showPointInput && _pointController.text.isNotEmpty) {
        try {
          double point = double.parse(_pointController.text);
          ContextModel cm = ContextModel();
          cm.bindVariable(Variable('x'), Number(point));
          double value = simplifiedDeriv.evaluate(EvaluationType.REAL, cm);
          _result = '在 x = $point 处的导数值: ${value.toStringAsFixed(4)}';
        } catch (e) {
          _result = '点的格式错误，请输入有效的数字';
        }
      } else {
        _result = _derivative;
      }
      });
    } catch (e) {
      setState(() {
        _result = '表达式解析错误，请检查格式\n支持的格式示例: x^2 + 3*x + sin(x)';
      _derivative = '';
      });
    }
  }

  void _clearAll() {
    setState(() {
      _functionController.clear();
      _pointController.clear();
      _result = '';
    _derivative = '';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('导数计算器', style: TextStyle(color: Colors.black)),
        backgroundColor: Colors.white,
        elevation: 1,
        actions: [
          IconButton(
            icon: Icon(Icons.info_outline),
            onPressed: () {
              _showInstructions();
            },
          ),
        ],
      ),
      body: Padding(
        padding: EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              '函数表达式 (以x为变量):',
              style: TextStyle(fontSize: 16, fontWeight: FontWeight.bold),
            ),
            SizedBox(height: 8),
            TextField(
              controller: _functionController,
              decoration: InputDecoration(
                hintText: '例如: x^2 + 3*x + sin(x)',
                border: OutlineInputBorder(),
                suffixIcon: IconButton(
                  icon: Icon(Icons.info),
                  onPressed: _showExpressionHelp,
                ),
              ),
            ),
            SizedBox(height: 16),

            // 计算某点导数值的选项
            Row(
              children: [
                Checkbox(
                  value: _showPointInput,
                  onChanged: (value) {
                    setState(() {
                      _showPointInput = value!;
                      if (!value) {
                        _pointController.clear();
                      }
                    });
                  },
                ),
                Text('计算某点处的导数值'),
              ],
            ),

            if (_showPointInput) ...[
              SizedBox(height: 8),
              Text(
                '输入点的x坐标:',
                style: TextStyle(fontSize: 14),
              ),
              SizedBox(height: 8),
              TextField(
                controller: _pointController,
                decoration: InputDecoration(
                  hintText: '例如: 2.5',
                  border: OutlineInputBorder(),
                ),
                keyboardType: TextInputType.numberWithOptions(decimal: true),
              ),
            ],

            SizedBox(height: 20),
            Row(
              children: [
                Expanded(
                  child: ElevatedButton(
                    onPressed: _calculateDerivative,
                    style: ElevatedButton.styleFrom(
                      backgroundColor: Colors.blue,
                      padding: EdgeInsets.symmetric(vertical: 12),
                    ),
                    child: Text('计算导数', style: TextStyle(color: Colors.white)),
                  ),
                ),
                SizedBox(width: 10),
                Expanded(
                  child: ElevatedButton(
                    onPressed: _clearAll,
                    style: ElevatedButton.styleFrom(
                      backgroundColor: Colors.grey,
                      padding: EdgeInsets.symmetric(vertical: 12),
                    ),
                    child: Text('清空', style: TextStyle(color: Colors.white)),
                  ),
                ),
              ],
            ),

            SizedBox(height: 20),
            if (_result.isNotEmpty) ...[
              Container(
                width: double.infinity,
                padding: EdgeInsets.all(16),
                decoration: BoxDecoration(
                  color: Colors.grey[50],
                  borderRadius: BorderRadius.circular(8),
                  border: Border.all(color: Colors.grey[300]!),
                ),
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    if (_derivative.isNotEmpty && _showPointInput) ...[
                      Text(
                        _derivative,
                        style: TextStyle(fontSize: 14, color: Colors.grey[700]),
                      ),
                      SizedBox(height: 8),
                    ],
                    Text(
                      _result,
                      style: TextStyle(
                        fontSize: 16,
                        fontWeight: FontWeight.bold,
                        color: Colors.blue[800],
                      ),
                    ),
                  ],
                ),
              ),
            ],

            Spacer(),
            _buildExamples(),
          ],
        ),
      ),
    );
  }

  Widget _buildExamples() {
    return Container(
      width: double.infinity,
      padding: EdgeInsets.all(16),
      decoration: BoxDecoration(
        color: Colors.blue[50],
        borderRadius: BorderRadius.circular(8),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Text(
            '表达式示例:',
            style: TextStyle(fontWeight: FontWeight.bold, color: Colors.blue[800]),
          ),
          SizedBox(height: 8),
          _buildExampleItem('x^2 + 3*x + 2'),
          _buildExampleItem('sin(x)'),
          _buildExampleItem('cos(x)'),
          _buildExampleItem('ln(x)'),
          _buildExampleItem('sqrt(x)'),
          _buildExampleItem('(x+1)/(x-1)'),
        ],
      ),
    );
  }

  Widget _buildExampleItem(String example) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _functionController.text = example;
        });
      },
      child: Padding(
        padding: EdgeInsets.symmetric(vertical: 4),
        child: Text(
          '• $example',
          style: TextStyle(color: Colors.blue[700], fontSize: 14),
        ),
      ),
    );
  }

  void _showInstructions() {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: Text('使用说明'),
        content: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            mainAxisSize: MainAxisSize.min,
            children: [
              Text('1. 输入以x为自变量的函数表达式'),
              SizedBox(height: 8),
              Text('2. 支持的基本函数:'),
              Text('   • sin(x), cos(x), tan(x)'),
              Text('   • ln(x) - 自然对数'),
              Text('   • sqrt(x) - 平方根'),
              SizedBox(height: 8),
              Text('3. 支持的操作符:'),
              Text('   • +, -, *, /'),
              Text('   • ^ - 幂运算'),
              Text('   • () - 括号'),
              SizedBox(height: 8),
              Text('4. 可选计算某点处的导数值'),
            ],
          ),
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: Text('确定'),
          ),
        ],
      ),
    );
  }

  void _showExpressionHelp() {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: Text('表达式格式帮助'),
        content: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            mainAxisSize: MainAxisSize.min,
            children: [
              Text('支持的数学表达式:'),
              SizedBox(height: 8),
              _buildHelpItem('x^2', 'x的平方'),
              _buildHelpItem('3*x', '3乘以x'),
              _buildHelpItem('sin(x)', '正弦函数'),
              _buildHelpItem('cos(x)', '余弦函数'),
              _buildHelpItem('ln(x)', '自然对数'),
              _buildHelpItem('sqrt(x)', '平方根'),
              _buildHelpItem('(x+1)/(x-1)', '分式'),
            ],
          ),
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: Text('确定'),
          ),
        ],
      ),
    );
  }

  Widget _buildHelpItem(String expression, String description) {
    return Padding(
      padding: EdgeInsets.symmetric(vertical: 4),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Container(
            width: 80,
            child: Text(
              expression,
              style: TextStyle(fontFamily: 'Monospace', fontWeight: FontWeight.bold),
            ),
          ),
          SizedBox(width: 10),
          Expanded(child: Text(description)),
        ],
      ),
    );
  }
}