// 班级码加入页面 — 学生/家长通过 6 位码加入班级
//
// 设计要点：
// - 6 位独立输入框，自动聚焦下一位
// - 输入完成后自动提交验证
// - 安全限制：5 次错误后锁定 30 分钟
// - 友好的状态反馈（验证中/成功/失败）

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:go_router/go_router.dart';

import '../../../core/constants/design_tokens.dart';
import '../bloc/auth_bloc.dart';

/// 班级码加入页面
class ClassCodeJoinPage extends StatefulWidget {
  const ClassCodeJoinPage({super.key});

  @override
  State<ClassCodeJoinPage> createState() => _ClassCodeJoinPageState();
}

class _ClassCodeJoinPageState extends State<ClassCodeJoinPage> {
  final List<TextEditingController> _controllers = List.generate(
    DesignTokens.classCodeLength,
    (_) => TextEditingController(),
  );
  final List<FocusNode> _focusNodes = List.generate(
    DesignTokens.classCodeLength,
    (_) => FocusNode(),
  );

  int _failedAttempts = 0;
  DateTime? _lockoutEndTime;

  /// 当前是否被锁定
  bool get _isCurrentlyLocked {
    if (_lockoutEndTime == null) return false;
    if (DateTime.now().isAfter(_lockoutEndTime!)) {
      _lockoutEndTime = null;
      return false;
    }
    return true;
  }

  @override
  void initState() {
    super.initState();
    // 自动聚焦第一个输入框
    WidgetsBinding.instance.addPostFrameCallback((_) {
      _focusNodes[0].requestFocus();
    });
  }

  @override
  void dispose() {
    for (final c in _controllers) {
      c.dispose();
    }
    for (final f in _focusNodes) {
      f.dispose();
    }
    super.dispose();
  }

  /// 获取当前输入的班级码
  String get _classCode => _controllers.map((c) => c.text).join();

  /// 是否所有位都已输入
  bool get _isComplete =>
      _controllers.every((c) => c.text.isNotEmpty);

  /// 清空所有输入框
  void _clearInputs() {
    for (final c in _controllers) {
      c.clear();
    }
    _focusNodes[0].requestFocus();
  }

  void _onChanged(int index, String value) {
    if (value.isEmpty && index > 0) {
      // 退格清空 → 跳到前一位
      _focusNodes[index - 1].requestFocus();
    } else if (value.isNotEmpty && index < DesignTokens.classCodeLength - 1) {
      // 输入字符 → 跳到下一位
      _focusNodes[index + 1].requestFocus();
    }

    // 全部输入完成 → 自动提交
    if (_isComplete) {
      _submit();
    }
  }

  void _submit() {
    if (!_isComplete || _isCurrentlyLocked) return;
    context.read<AuthBloc>().add(ClassCodeSubmitted(_classCode));
  }

  /// 处理 AuthBloc 状态变化
  void _handleAuthState(BuildContext context, AuthState state) {
    if (state is! Authenticated) return;

    // 成功加入班级
    if (!state.needsClassCode) {
      context.go('/home');
      return;
    }

    // 班级码验证错误
    final error = state.classCodeError;
    if (error != null && error.isNotEmpty) {
      _failedAttempts++;

      // 检查是否为锁定错误
      if (error.contains('30 分钟') || error.contains('尝试次数过多')) {
        setState(() {
          _lockoutEndTime = DateTime.now().add(
            Duration(minutes: DesignTokens.classCodeLockoutMinutes),
          );
        });
      }

      // 清空输入
      _clearInputs();

      // 显示错误提示
      if (mounted) {
        ScaffoldMessenger.of(context).clearSnackBars();
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(
            content: Text(error),
            backgroundColor: Theme.of(context).colorScheme.error,
            duration: const Duration(seconds: 3),
          ),
        );
      }
    }
  }

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

    return BlocListener<AuthBloc, AuthState>(
      listener: _handleAuthState,
      child: Scaffold(
        body: SafeArea(
          child: Padding(
            padding: const EdgeInsets.symmetric(
              horizontal: DesignTokens.spacing24,
            ),
            child: Column(
              children: [
                const Spacer(flex: 2),

                // 标题
                Icon(
                  Icons.groups_rounded,
                  size: 64,
                  color: colorScheme.primary,
                ),
                const SizedBox(height: DesignTokens.spacing24),
                Text(
                  '加入班级',
                  style: Theme.of(context).textTheme.headlineMedium?.copyWith(
                        fontWeight: FontWeight.bold,
                      ),
                ),
                const SizedBox(height: DesignTokens.spacing8),
                Text(
                  '输入老师提供的 6 位班级码',
                  style: Theme.of(context).textTheme.bodyLarge?.copyWith(
                        color: colorScheme.onSurface.withValues(alpha: 0.6),
                      ),
                ),
                const SizedBox(height: DesignTokens.spacing48),

                // 锁定状态 or 输入框
                if (_isCurrentlyLocked)
                  _buildLockoutView(context, colorScheme)
                else
                  _buildCodeInputs(context, colorScheme),

                const SizedBox(height: DesignTokens.spacing24),

                // 跳过按钮
                TextButton(
                  onPressed: () => context.go('/home'),
                  child: Text(
                    '稍后再加入',
                    style: TextStyle(
                      color: colorScheme.onSurface.withValues(alpha: 0.5),
                    ),
                  ),
                ),

                // 剩余尝试次数提示
                if (!_isCurrentlyLocked && _failedAttempts > 0)
                  Padding(
                    padding: const EdgeInsets.only(top: 8),
                    child: Text(
                      '剩余 ${DesignTokens.classCodeMaxAttempts - _failedAttempts} 次尝试机会',
                      style: Theme.of(context).textTheme.bodySmall?.copyWith(
                            color: _failedAttempts >= 4
                                ? colorScheme.error
                                : colorScheme.onSurface.withValues(alpha: 0.5),
                          ),
                    ),
                  ),

                const Spacer(flex: 3),
              ],
            ),
          ),
        ),
      ),
    );
  }

  /// 锁定视图 — 超过最大尝试次数后显示
  Widget _buildLockoutView(BuildContext context, ColorScheme colorScheme) {
    return Column(
      children: [
        Icon(Icons.lock_outline, size: 48, color: colorScheme.error),
        const SizedBox(height: 16),
        Text(
          '尝试次数过多',
          style: Theme.of(context).textTheme.titleMedium?.copyWith(
                fontWeight: FontWeight.bold,
              ),
        ),
        const SizedBox(height: 8),
        Text(
          '请等待 ${DesignTokens.classCodeLockoutMinutes} 分钟后再试',
          style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                color: colorScheme.onSurface.withValues(alpha: 0.6),
              ),
        ),
      ],
    );
  }

  /// 6 位班级码输入框
  Widget _buildCodeInputs(BuildContext context, ColorScheme colorScheme) {
    return BlocBuilder<AuthBloc, AuthState>(
      builder: (context, state) {
        final isLoading = state is Authenticated && state.isLoading;

        return Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: List.generate(
            DesignTokens.classCodeLength,
            (index) => _buildCodeInput(context, index, colorScheme, isLoading),
          ),
        );
      },
    );
  }

  /// 单个班级码输入框
  Widget _buildCodeInput(
    BuildContext context,
    int index,
    ColorScheme colorScheme,
    bool isLoading,
  ) {
    return SizedBox(
      width: 48,
      height: 56,
      child: TextField(
        controller: _controllers[index],
        focusNode: _focusNodes[index],
        enabled: !isLoading,
        textAlign: TextAlign.center,
        textAlignVertical: TextAlignVertical.center,
        style: Theme.of(context).textTheme.headlineSmall?.copyWith(
              fontWeight: FontWeight.bold,
              letterSpacing: 0,
            ),
        maxLength: 1,
        keyboardType: TextInputType.text,
        textCapitalization: TextCapitalization.characters,
        decoration: InputDecoration(
          counterText: '',
          filled: true,
          fillColor: colorScheme.surfaceContainerHighest.withValues(alpha: 0.5),
          border: OutlineInputBorder(
            borderRadius: BorderRadius.circular(12),
            borderSide: BorderSide.none,
          ),
          focusedBorder: OutlineInputBorder(
            borderRadius: BorderRadius.circular(12),
            borderSide: BorderSide(color: colorScheme.primary, width: 2),
          ),
        ),
        onChanged: (value) => _onChanged(index, value),
        onSubmitted: (_) {
          if (_isComplete) _submit();
        },
      ),
    );
  }
}