nj/app/lib/features/auth/views/class_code_join_page.dart

// 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(),
  );

  @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);

  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) return;
    context.read<AuthBloc>().add(ClassCodeSubmitted(_classCode));

    // 提交后跳转到首页（班级码验证由 BLoC 处理）
    final state = context.read<AuthBloc>().state;
    if (state is Authenticated && !state.needsClassCode) {
      context.go('/home');
    }
  }

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

    return 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),

              // 6 位输入框
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: List.generate(
                  DesignTokens.classCodeLength,
                  (index) => _buildCodeInput(context, index, 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),
                  ),
                ),
              ),

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

  /// 单个班级码输入框
  Widget _buildCodeInput(BuildContext context, int index, ColorScheme colorScheme) {
    return SizedBox(
      width: 48,
      height: 56,
      child: TextField(
        controller: _controllers[index],
        focusNode: _focusNodes[index],
        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();
        },
      ),
    );
  }
}