import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_math_fork/flutter_math.dart';
import 'package:provider/provider.dart';

import 'curve_plot.dart';
import 'symja.dart';
import 'symja_functions.dart';

/// 科学计算器（默认主界面）。
///
/// 表达式用**字符串**表示，按键在光标处插入 —— 这是 Q28b 定的第一阶段。
/// 结构化节点输入（节点树 / 槽 / 选区）是后续独立的升级，但下游接口不变：
/// 求值、历史、双界面看到的始终是一个表达式字符串。
class CalculatorPage extends StatefulWidget {
  const CalculatorPage({super.key});

  @override
  State<CalculatorPage> createState() => _CalculatorPageState();
}

class _CalculatorPageState extends State<CalculatorPage> {
  final _ctrl = TextEditingController();
  final _focus = FocusNode();

  /// 边输入边算的结果（不算历史、不动 `%`）。
  SymjaResult? _preview;

  /// 按 = 提交后的结果。
  SymjaResult? _committed;
  String? _error;

  Timer? _debounce;
  int _seq = 0;

  @override
  void dispose() {
    _debounce?.cancel();
    _ctrl.dispose();
    _focus.dispose();
    super.dispose();
  }

  // ------------------------------------------------------------------ 表达式编辑

  /// 在光标处插入 [text]，并把光标往回退 [back] 位（用于 `Integrate[□, x]` 这类模板）。
  void _insert(String text, {int back = 0}) {
    final v = _ctrl.value;
    final sel = v.selection;
    final start = sel.isValid ? sel.start : v.text.length;
    final end = sel.isValid ? sel.end : v.text.length;

    final newText = v.text.replaceRange(start, end, text);
    _ctrl.value = TextEditingValue(
      text: newText,
      selection:
          TextSelection.collapsed(offset: start + text.length - back),
    );
    _onChanged();
  }

  void _backspace() {
    final v = _ctrl.value;
    final sel = v.selection;
    final start = sel.isValid ? sel.start : v.text.length;
    final end = sel.isValid ? sel.end : v.text.length;
    if (start == end && start == 0) return;
    final from = start == end ? start - 1 : start;
    final newText = v.text.replaceRange(from, end, '');
    _ctrl.value = TextEditingValue(
      text: newText,
      selection: TextSelection.collapsed(offset: from),
    );
    _onChanged();
  }

  void _clear() {
    _ctrl.clear();
    setState(() {
      _preview = null;
      _committed = null;
      _error = null;
    });
  }

  void _onChanged() {
    setState(() {
      _committed = null;
      _error = null;
    });
    _debounce?.cancel();
    // 防抖：按键连打时不要每个字符都过一次通道
    _debounce = Timer(const Duration(milliseconds: 500), _runPreview);
  }

  Future<void> _runPreview() async {
    final expr = _ctrl.text.trim();
    if (expr.isEmpty) {
      if (mounted) setState(() => _preview = null);
      return;
    }
    final session = context.read<SymjaSession>();
    final id = ++_seq;
    final r = await session.preview(expr);
    if (!mounted || id != _seq) return; // 已有更新的预览在路上
    setState(() => _preview = r);
  }

  // ------------------------------------------------------------------ 提交

  Future<void> _commit() async {
    final expr = _ctrl.text.trim();
    if (expr.isEmpty) return;
    _debounce?.cancel();
    final session = context.read<SymjaSession>();
    final id = ++_seq; // 让在途的预览作废
    try {
      final r = await session.evaluate(expr);
      if (!mounted || id != _seq) return;
      setState(() {
        _committed = r;
        _preview = null;
        _error = null;
      });
    } on SymjaException catch (e) {
      if (!mounted || id != _seq) return;
      setState(() {
        _error = '$e';
        _committed = null;
        _preview = null;
      });
    }
    await session.refreshVariables();
  }

  /// 把当前表达式在 x ∈ [-6.3, 6.3] 上采样并画出来。
  Future<void> _plotCurrent() async {
    final expr = _ctrl.text.trim();
    if (expr.isEmpty) return;
    final session = context.read<SymjaSession>();
    final messenger = ScaffoldMessenger.of(context);
    try {
      final s = await session.sample(expr, from: -6.3, to: 6.3, count: 240);
      if (!mounted) return;
      await showDialog<void>(
        context: context,
        builder: (_) => AlertDialog(
          title: Text('$expr   （${s.ys.length} 点，${s.elapsedMs} ms）'),
          content: SizedBox(
            width: 360,
            height: 280,
            child: CurvePlot(series: [
              CurveSeries(
                label: expr,
                color: const Color(0xFF3F51B5),
                points: [
                  for (var i = 0; i < s.ys.length; i++)
                    Offset(s.xAt(i), s.ys[i]),
                ],
              ),
            ]),
          ),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('关闭'),
            ),
          ],
        ),
      );
    } on SymjaException catch (e) {
      messenger.showSnackBar(SnackBar(content: Text('$e')));
    }
  }

  Future<void> _showPalette() async {
    // 面板返回「要插入什么」+「光标从末尾回退几位」：
    // 函数是 `Sin[]` 退 1（光标在括号里），常量是 `Pi` 退 0。
    final picked = await showModalBottomSheet<({String text, int back})>(
      context: context,
      isScrollControlled: true,
      showDragHandle: true,
      builder: (_) => const _FunctionPalette(),
    );
    if (picked != null) _insert(picked.text, back: picked.back);
  }

  // ------------------------------------------------------------------ UI

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('计算器'),
        actions: [
          IconButton(
            tooltip: '画图（x ∈ [-6.3, 6.3]）',
            icon: const Icon(Icons.show_chart),
            onPressed: _plotCurrent,
          ),
          IconButton(
            tooltip: '函数面板',
            icon: const Icon(Icons.functions),
            onPressed: _showPalette,
          ),
          IconButton(
            tooltip: '清空',
            icon: const Icon(Icons.refresh),
            onPressed: _clear,
          ),
        ],
      ),
      body: SafeArea(
        child: Column(
          children: [
            _display(context),
            const Divider(height: 1),
            Expanded(child: _keypad(context)),
          ],
        ),
      ),
    );
  }

  Widget _display(BuildContext context) {
    final scheme = Theme.of(context).colorScheme;
    final shown = _committed ?? _preview;

    return Container(
      width: double.infinity,
      padding: const EdgeInsets.fromLTRB(16, 12, 16, 12),
      color: scheme.surfaceContainerLow,
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        children: [
          TextField(
            controller: _ctrl,
            focusNode: _focus,
            maxLines: 3,
            minLines: 1,
            textAlign: TextAlign.right,
            style: const TextStyle(fontFamily: 'monospace', fontSize: 18),
            decoration: const InputDecoration(
              isDense: true,
              border: InputBorder.none,
              hintText: '按下面的键，或点这里用键盘输入',
            ),
            onChanged: (_) => _onChanged(),
            onSubmitted: (_) => _commit(),
          ),
          const SizedBox(height: 8),
          SizedBox(
            height: 56,
            child: Align(
              alignment: Alignment.centerRight,
              child: SingleChildScrollView(
                scrollDirection: Axis.horizontal,
                reverse: true,
                child: _resultView(context, shown),
              ),
            ),
          ),
        ],
      ),
    );
  }

  Widget _resultView(BuildContext context, SymjaResult? shown) {
    final scheme = Theme.of(context).colorScheme;

    if (_error != null) {
      return SelectableText(
        _error!,
        style: TextStyle(
          fontFamily: 'monospace',
          fontSize: 13,
          color: scheme.error,
        ),
      );
    }
    if (shown == null) {
      return Text(
        _ctrl.text.trim().isEmpty ? '' : '…',
        style: TextStyle(fontSize: 22, color: scheme.outline),
      );
    }

    final plain = SelectableText(
      shown.text,
      style: const TextStyle(fontFamily: 'monospace', fontSize: 22),
    );
    final tex = shown.tex;
    final body = tex == null
        ? plain
        : Math.tex(
            tex,
            mathStyle: MathStyle.display,
            textStyle: TextStyle(fontSize: 26, color: scheme.onSurface),
            onErrorFallback: (_) => plain,
          );

    return Row(
      mainAxisSize: MainAxisSize.min,
      children: [
        if (_committed != null) ...[
          Icon(Icons.check_circle, size: 16, color: scheme.primary),
          const SizedBox(width: 6),
          Text('${_committed!.elapsedMs} ms',
              style: TextStyle(fontSize: 11, color: scheme.outline)),
          const SizedBox(width: 10),
        ],
        body,
      ],
    );
  }

  Widget _keypad(BuildContext context) {
    return LayoutBuilder(
      builder: (context, box) {
        const rows = <List<_Key>>[
          [
            _Key('∫', insert: 'Integrate[', after: ', x]'),
            _Key('Σ', insert: 'Sum[', after: ', {n, 1, Infinity}]'),
            _Key('d/dx', insert: 'D[', after: ', x]'),
            _Key('lim', insert: 'Limit[', after: ', x->0]'),
            _Key('solve', insert: 'Solve[', after: ', x]'),
          ],
          [
            _Key('sin', insert: 'Sin[', after: ']'),
            _Key('cos', insert: 'Cos[', after: ']'),
            _Key('tan', insert: 'Tan[', after: ']'),
            _Key('ln', insert: 'Log[', after: ']'),
            _Key('√', insert: 'Sqrt[', after: ']'),
          ],
          [
            _Key('7', insert: '7'),
            _Key('8', insert: '8'),
            _Key('9', insert: '9'),
            _Key('(', insert: '('),
            _Key(')', insert: ')'),
          ],
          [
            _Key('4', insert: '4'),
            _Key('5', insert: '5'),
            _Key('6', insert: '6'),
            _Key('×', insert: '*'),
            _Key('÷', insert: '/'),
          ],
          [
            _Key('1', insert: '1'),
            _Key('2', insert: '2'),
            _Key('3', insert: '3'),
            _Key('+', insert: '+'),
            _Key('−', insert: '-'),
          ],
          [
            _Key('0', insert: '0'),
            _Key('.', insert: '.'),
            _Key('^', insert: '^'),
            // 变量键：没有它们就没法只用按钮写出 Integrate[x^2, x]。
            // π / e 挪进了函数面板（那里的常量是可以点的）。
            _Key('x', insert: 'x'),
            _Key('n', insert: 'n'),
          ],
          [
            _Key('⌫', action: _KeyAction.backspace, tint: true),
            _Key('CLR', action: _KeyAction.clear, tint: true),
            _Key(',', insert: ', '),
            _Key('ANS', insert: '%', tint: true),
            _Key('=', action: _KeyAction.commit, primary: true),
          ],
        ];

        // 7 行 + 6 个 6px 间隙，再扣掉 Padding 的上下各 6px ——
        // box.maxHeight 是 padding **之前**的高度，漏掉这一项会溢出 12px。
        const gaps = 6 * 6.0;
        const padding = 12.0;
        final h = (box.maxHeight - padding - gaps) / 7;
        return Padding(
          padding: const EdgeInsets.all(6),
          child: Column(
            children: [
              for (var r = 0; r < rows.length; r++) ...[
                if (r > 0) const SizedBox(height: 6),
                SizedBox(
                  height: h,
                  child: Row(
                    children: [
                      for (var c = 0; c < rows[r].length; c++) ...[
                        if (c > 0) const SizedBox(width: 6),
                        Expanded(child: _keyButton(rows[r][c])),
                      ],
                    ],
                  ),
                ),
              ],
            ],
          ),
        );
      },
    );
  }

  Widget _keyButton(_Key k) {
    final scheme = Theme.of(context).colorScheme;
    final bg = k.primary
        ? scheme.primary
        : k.tint
            ? scheme.surfaceContainerHighest
            : scheme.surfaceContainerLow;
    final fg = k.primary ? scheme.onPrimary : scheme.onSurface;

    return Material(
      color: bg,
      borderRadius: BorderRadius.circular(10),
      child: InkWell(
        borderRadius: BorderRadius.circular(10),
        onTap: () {
          switch (k.action) {
            case _KeyAction.insert:
              // 模板形如 Insert[□, x]：先插前半段，再插后半段，光标夹在中间
              _insert(k.insert + (k.after ?? ''), back: (k.after ?? '').length);
            case _KeyAction.backspace:
              _backspace();
            case _KeyAction.clear:
              _clear();
            case _KeyAction.commit:
              _commit();
            case null:
              _insert(k.insert);
          }
        },
        child: Center(
          child: Text(
            k.label,
            style: TextStyle(
              color: fg,
              fontSize: k.label.length > 2 ? 13 : 17,
              fontFamily: k.label.length > 2 ? null : 'monospace',
            ),
          ),
        ),
      ),
    );
  }
}

enum _KeyAction { insert, backspace, clear, commit }

@immutable
class _Key {
  final String label;

  /// 插入的文本（模板时是前半段）。
  final String insert;

  /// 模板的后半段；光标会停在 [insert] 与 [after] 之间。
  final String? after;

  final _KeyAction? action;
  final bool tint;
  final bool primary;

  const _Key(
    this.label, {
    this.insert = '',
    this.after,
    this.action = _KeyAction.insert,
    this.tint = false,
    this.primary = false,
  });
}

/// 函数面板：检索 Symja 的两百多个函数，选中后插入 `Name[]`。
class _FunctionPalette extends StatefulWidget {
  const _FunctionPalette();

  @override
  State<_FunctionPalette> createState() => _FunctionPaletteState();
}

class _FunctionPaletteState extends State<_FunctionPalette> {
  final _search = TextEditingController();
  String _q = '';

  @override
  void dispose() {
    _search.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final q = _q.trim().toLowerCase();
    final fns = kSymjaFunctions
        .where((f) => q.isEmpty || f.toLowerCase().contains(q))
        .toList(growable: false);

    return DraggableScrollableSheet(
      expand: false,
      initialChildSize: 0.75,
      maxChildSize: 0.95,
      builder: (context, scroll) => Column(
        children: [
          Padding(
            padding: const EdgeInsets.fromLTRB(16, 0, 16, 8),
            child: TextField(
              controller: _search,
              autofocus: true,
              decoration: InputDecoration(
                isDense: true,
                hintText: '函数名（共 ${kSymjaFunctions.length} 个）',
                prefixIcon: const Icon(Icons.search),
                border: const OutlineInputBorder(),
              ),
              onChanged: (v) => setState(() => _q = v),
            ),
          ),
          // 常量做成可点的 —— 它们从键盘上挪走了，得有个地方能按。
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 16),
            child: Wrap(
              spacing: 8,
              runSpacing: 4,
              crossAxisAlignment: WrapCrossAlignment.center,
              children: [
                Text('常量',
                    style: Theme.of(context).textTheme.bodySmall),
                for (final c in kSymjaConstants)
                  ActionChip(
                    label: Text(
                      c,
                      style: const TextStyle(
                          fontFamily: 'monospace', fontSize: 12),
                    ),
                    visualDensity: VisualDensity.compact,
                    materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
                    onPressed: () =>
                        Navigator.pop(context, (text: c, back: 0)),
                  ),
              ],
            ),
          ),
          const Divider(height: 16),
          Expanded(
            child: fns.isEmpty
                ? const Center(child: Text('没有匹配的函数'))
                : ListView.builder(
                    controller: scroll,
                    itemCount: fns.length,
                    itemBuilder: (_, i) => ListTile(
                      dense: true,
                      title: Text(
                        fns[i],
                        style: const TextStyle(fontFamily: 'monospace'),
                      ),
                      onTap: () => Navigator.pop(
                          context, (text: '${fns[i]}[]', back: 1)),
                    ),
                  ),
          ),
        ],
      ),
    );
  }
}