import 'package:flutter/material.dart';
import 'package:shadcn_ui/shadcn_ui.dart';
import '../home/home_page.dart';
import '../market/market_page.dart';
import '../trade/trade_page.dart';
import '../asset/asset_page.dart';
import '../mine/mine_page.dart';

/// 底部导航项
class _NavItem {
  final String label;
  final IconData icon;
  final Widget page;

  const _NavItem({required this.label, required this.icon, required this.page});
}

/// 主页面（使用 shadcn_ui 风格）
class MainPage extends StatefulWidget {
  const MainPage({super.key});

  @override
  State<MainPage> createState() => _MainPageState();
}

class _MainPageState extends State<MainPage> {
  int _currentIndex = 0;
  final Set<int> _loadedPages = {0};

  static const _navItems = [
    _NavItem(label: '首页', icon: LucideIcons.house, page: HomePage()),
    _NavItem(label: '行情', icon: LucideIcons.trendingUp, page: MarketPage()),
    _NavItem(label: '交易', icon: LucideIcons.arrowLeftRight, page: TradePage()),
    _NavItem(label: '资产', icon: LucideIcons.wallet, page: AssetPage()),
    _NavItem(label: '我的', icon: LucideIcons.user, page: MinePage()),
  ];

  void _onTabChanged(int index) {
    setState(() {
      _currentIndex = index;
      _loadedPages.add(index);
    });
  }

  @override
  Widget build(BuildContext context) {
    final theme = ShadTheme.of(context);

    return Scaffold(
      body: LazyIndexedStack(
        index: _currentIndex,
        loadedIndexes: _loadedPages,
        children: _navItems.map((item) => item.page).toList(),
      ),
      bottomNavigationBar: _BottomNavBar(
        items: _navItems,
        currentIndex: _currentIndex,
        onTap: _onTabChanged,
      ),
    );
  }
}

/// 底部导航栏
class _BottomNavBar extends StatelessWidget {
  final List<_NavItem> items;
  final int currentIndex;
  final ValueChanged<int> onTap;

  const _BottomNavBar({
    required this.items,
    required this.currentIndex,
    required this.onTap,
  });

  @override
  Widget build(BuildContext context) {
    final theme = ShadTheme.of(context);

    return Container(
      decoration: BoxDecoration(
        color: theme.colorScheme.background,
        border: Border(top: BorderSide(color: theme.colorScheme.border)),
      ),
      child: SafeArea(
        child: Padding(
          padding: const EdgeInsets.symmetric(vertical: 8),
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: items.asMap().entries.map((entry) {
              return _NavItemWidget(
                item: entry.value,
                isSelected: entry.key == currentIndex,
                onTap: () => onTap(entry.key),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}

/// 导航项组件
class _NavItemWidget extends StatelessWidget {
  final _NavItem item;
  final bool isSelected;
  final VoidCallback onTap;

  const _NavItemWidget({
    required this.item,
    required this.isSelected,
    required this.onTap,
  });

  @override
  Widget build(BuildContext context) {
    final theme = ShadTheme.of(context);
    final color = isSelected ? theme.colorScheme.primary : theme.colorScheme.mutedForeground;

    return GestureDetector(
      onTap: onTap,
      behavior: HitTestBehavior.opaque,
      child: Container(
        padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Icon(item.icon, color: color, size: 24),
            const SizedBox(height: 4),
            Text(
              item.label,
              style: TextStyle(
                fontSize: 12,
                color: color,
                fontWeight: isSelected ? FontWeight.w600 : FontWeight.normal,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

/// 懒加载 IndexedStack - 只渲染已访问过的页面
class LazyIndexedStack extends StatefulWidget {
  final int index;
  final Set<int> loadedIndexes;
  final List<Widget> children;

  const LazyIndexedStack({
    super.key,
    required this.index,
    required this.loadedIndexes,
    required this.children,
  });

  @override
  State<LazyIndexedStack> createState() => _LazyIndexedStackState();
}

class _LazyIndexedStackState extends State<LazyIndexedStack> {
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: widget.children.asMap().entries.map((entry) {
        final isVisible = entry.key == widget.index;
        final isLoaded = widget.loadedIndexes.contains(entry.key);

        return Positioned.fill(
          child: Offstage(
            offstage: !isVisible,
            child: TickerMode(
              enabled: isVisible,
              child: isLoaded ? entry.value : const SizedBox.shrink(),
            ),
          ),
        );
      }).toList(),
    );
  }
}