import 'package:flutter/material.dart';

/// 文档与帮助页：内容区留空，底部是可上滑的 LLM 助手对话框。
class DocsPage extends StatelessWidget {
  const DocsPage({super.key});

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colors = theme.colorScheme;

    return Scaffold(
      appBar: AppBar(title: const Text('文档与帮助')),
      body: LayoutBuilder(
        builder: (BuildContext context, BoxConstraints constraints) {
          return Stack(
            children: <Widget>[
              // 内容区：整体留白，只保留底色和边框，深浅色都跟随主题。
              Padding(
                padding: const EdgeInsets.all(16),
                child: Container(
                  width: double.infinity,
                  decoration: BoxDecoration(
                    color: colors.surfaceContainerLow,
                    borderRadius: BorderRadius.circular(20),
                    border: Border.all(color: colors.outlineVariant),
                  ),
                  alignment: Alignment.center,
                  child: Text(
                    '文档内容将在这里显示',
                    style: theme.textTheme.bodyMedium?.copyWith(
                      color: colors.onSurfaceVariant,
                    ),
                  ),
                ),
              ),
              _AssistantSheet(availableHeight: constraints.maxHeight),
            ],
          );
        },
      ),
    );
  }
}

/// 底部助手：收起时只露出一条，上滑或点击后展开成对话框。
class _AssistantSheet extends StatefulWidget {
  const _AssistantSheet({required this.availableHeight});

  /// 父级可用高度，用于把拖拽像素换算成比例。
  final double availableHeight;

  @override
  State<_AssistantSheet> createState() => _AssistantSheetState();
}

class _AssistantSheetState extends State<_AssistantSheet> {
  static const double _collapsed = 0.13;
  static const double _expandedSize = 0.92;

  final DraggableScrollableController _controller =
      DraggableScrollableController();
  final TextEditingController _input = TextEditingController();

  static const List<(bool, String)> _messages = <(bool, String)>[
    (
      false,
      '你好，我是 KiriMemo 的助手。文档还没接入，但关于用法和概念的问题可以先问我。',
    ),
  ];

  @override
  void dispose() {
    _controller.dispose();
    _input.dispose();
    super.dispose();
  }

  void _animateTo(double target) {
    if (!_controller.isAttached) {
      return;
    }
    _controller.animateTo(
      target,
      duration: const Duration(milliseconds: 260),
      curve: Curves.easeOutCubic,
    );
  }

  void _toggle() {
    if (!_controller.isAttached) {
      return;
    }
    final bool open = _controller.size > 0.4;
    _animateTo(open ? _collapsed : _expandedSize);
  }

  void _onDragUpdate(DragUpdateDetails details) {
    if (!_controller.isAttached || widget.availableHeight <= 0) {
      return;
    }
    final double next =
        (_controller.size - details.delta.dy / widget.availableHeight)
            .clamp(_collapsed, _expandedSize);
    _controller.jumpTo(next);
  }

  void _onDragEnd(DragEndDetails details) {
    if (!_controller.isAttached) {
      return;
    }
    final bool open =
        _controller.size > (_collapsed + _expandedSize) / 2;
    _animateTo(open ? _expandedSize : _collapsed);
  }

  void _send() {
    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(
        content: Text('助手尚未接入模型'),
        behavior: SnackBarBehavior.floating,
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colors = theme.colorScheme;

    return DraggableScrollableSheet(
      controller: _controller,
      initialChildSize: _collapsed,
      minChildSize: _collapsed,
      maxChildSize: _expandedSize,
      builder: (BuildContext context, ScrollController scrollController) {
        return Container(
          decoration: BoxDecoration(
            color: colors.surfaceContainerHigh,
            borderRadius: const BorderRadius.vertical(top: Radius.circular(24)),
            border: Border(top: BorderSide(color: colors.outlineVariant)),
          ),
          child: LayoutBuilder(
            builder: (BuildContext context, BoxConstraints constraints) {
              final bool expanded = constraints.maxHeight > 200;
              return Column(
                children: <Widget>[
                  GestureDetector(
                    behavior: HitTestBehavior.opaque,
                    onTap: _toggle,
                    onVerticalDragUpdate: _onDragUpdate,
                    onVerticalDragEnd: _onDragEnd,
                    child: _header(theme, colors, expanded: expanded),
                  ),
                  // 列表必须始终挂载：DraggableScrollableController 的
                  // isAttached 取决于内部 ScrollController 是否有 client，
                  // 收起时若拿掉列表，就再也展不开了。
                  Expanded(
                    child: ListView(
                      controller: scrollController,
                      padding: const EdgeInsets.fromLTRB(16, 0, 16, 12),
                      children: <Widget>[
                        if (expanded)
                          for (final (bool fromUser, String text) in _messages)
                            _Bubble(fromUser: fromUser, text: text),
                      ],
                    ),
                  ),
                  if (expanded) _inputRow(theme, colors),
                ],
              );
            },
          ),
        );
      },
    );
  }

  Widget _header(
    ThemeData theme,
    ColorScheme colors, {
    required bool expanded,
  }) {
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 8, 16, 10),
      child: Column(
        children: <Widget>[
          Container(
            width: 36,
            height: 4,
            decoration: BoxDecoration(
              color: colors.onSurfaceVariant.withValues(alpha: 0.4),
              borderRadius: BorderRadius.circular(2),
            ),
          ),
          const SizedBox(height: 12),
          Row(
            children: <Widget>[
              Icon(Icons.auto_awesome_rounded, size: 18, color: colors.primary),
              const SizedBox(width: 8),
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: <Widget>[
                    Text('问问 KiriMemo', style: theme.textTheme.titleSmall),
                    // 收起时只有一条横栏，放不下副标题就不放。
                    if (expanded)
                      Text(
                        '文档暂未接入，可以先问概念与用法',
                        maxLines: 1,
                        overflow: TextOverflow.ellipsis,
                        style: theme.textTheme.bodySmall?.copyWith(
                          color: colors.onSurfaceVariant,
                        ),
                      ),
                  ],
                ),
              ),
              Icon(
                expanded
                    ? Icons.keyboard_arrow_down_rounded
                    : Icons.keyboard_arrow_up_rounded,
                color: colors.onSurfaceVariant,
              ),
            ],
          ),
        ],
      ),
    );
  }

  Widget _inputRow(ThemeData theme, ColorScheme colors) {
    return Padding(
      padding: EdgeInsets.fromLTRB(
        16,
        0,
        16,
        12 + MediaQuery.viewPaddingOf(context).bottom,
      ),
      child: Row(
        children: <Widget>[
          Expanded(
            child: TextField(
              controller: _input,
              textInputAction: TextInputAction.send,
              onSubmitted: (_) => _send(),
              decoration: InputDecoration(
                hintText: '问点什么…',
                isDense: true,
                filled: true,
                fillColor: colors.surfaceContainerHighest,
                contentPadding: const EdgeInsets.symmetric(
                  horizontal: 16,
                  vertical: 12,
                ),
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(24),
                  borderSide: BorderSide.none,
                ),
              ),
            ),
          ),
          const SizedBox(width: 8),
          IconButton.filled(
            onPressed: _send,
            icon: const Icon(Icons.arrow_upward_rounded),
            tooltip: '发送',
          ),
        ],
      ),
    );
  }
}

class _Bubble extends StatelessWidget {
  const _Bubble({required this.fromUser, required this.text});

  final bool fromUser;
  final String text;

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colors = theme.colorScheme;

    return Align(
      alignment: fromUser ? Alignment.centerRight : Alignment.centerLeft,
      child: Container(
        margin: const EdgeInsets.only(bottom: 10),
        padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 10),
        constraints: const BoxConstraints(maxWidth: 320),
        decoration: BoxDecoration(
          color: fromUser
              ? colors.primaryContainer
              : colors.surfaceContainerHighest,
          borderRadius: BorderRadius.only(
            topLeft: const Radius.circular(16),
            topRight: const Radius.circular(16),
            bottomLeft: Radius.circular(fromUser ? 16 : 4),
            bottomRight: Radius.circular(fromUser ? 4 : 16),
          ),
        ),
        child: Text(
          text,
          style: theme.textTheme.bodyMedium?.copyWith(
            color: fromUser ? colors.onPrimaryContainer : colors.onSurface,
          ),
        ),
      ),
    );
  }
}