import 'package:flutter/material.dart';
import 'package:flutter/semantics.dart';
import 'package:flutter/services.dart';
import 'package:patbond_flutter/core/navigation/fade_route.dart';
import 'package:patbond_flutter/core/network/api_exception.dart';
import 'package:patbond_flutter/core/theme/app_theme.dart';
import 'package:patbond_flutter/core/widgets/app_text_field.dart';
import 'package:patbond_flutter/core/widgets/auth_scaffold.dart';
import 'package:patbond_flutter/core/widgets/brand_mark.dart';
import 'package:patbond_flutter/core/widgets/inline_error_banner.dart';
import 'package:patbond_flutter/core/widgets/primary_button.dart';
import 'package:patbond_flutter/features/auth/auth_repository.dart';
import 'package:patbond_flutter/features/auth/register_page.dart';

enum _Field { account, password }

/// 登录页（12 号组装稿 §5）。登录成功后由认证状态机切入主壳。
class LoginPage extends StatefulWidget {
  const LoginPage({required this.authRepository, super.key});

  final AuthRepository authRepository;

  @override
  State<LoginPage> createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  final _accountCtrl = TextEditingController();
  final _passwordCtrl = TextEditingController();
  String? _accountError;
  String? _passwordError;
  String? _formError;
  bool _submitting = false;

  @override
  void dispose() {
    _accountCtrl.dispose();
    _passwordCtrl.dispose();
    super.dispose();
  }

  String? _validateAccount() =>
      _accountCtrl.text.trim().isEmpty ? '请输入用户名或手机号' : null;

  String? _validatePassword() =>
      _passwordCtrl.text.trim().isEmpty ? '请输入密码' : null;

  void _validateAccountOnBlur() {
    if (!mounted) return;
    setState(() => _accountError = _validateAccount());
  }

  void _validatePasswordOnBlur() {
    if (!mounted) return;
    setState(() => _passwordError = _validatePassword());
  }

  /// 字段变更即清除本字段错误与表单级横幅。
  void _clearErrors({required _Field field}) {
    if (_formError == null &&
        (field == _Field.account ? _accountError : _passwordError) == null) {
      return;
    }
    setState(() {
      _formError = null;
      if (field == _Field.account) _accountError = null;
      if (field == _Field.password) _passwordError = null;
    });
  }

  void _showFormError(String message) {
    setState(() => _formError = message);
    SemanticsService.sendAnnouncement(
      View.of(context),
      message,
      TextDirection.ltr,
    );
  }

  void _showNetworkSnackBar() {
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(
        content: const Text('网络异常，请检查网络后重试'),
        action: SnackBarAction(label: '重试', onPressed: _submit),
      ),
    );
  }

  Future<void> _submit() async {
    if (_submitting) return;
    final accountError = _validateAccount();
    final passwordError = _validatePassword();
    if (accountError != null || passwordError != null) {
      setState(() {
        _accountError = accountError;
        _passwordError = passwordError;
      });
      return;
    }
    setState(() {
      _submitting = true;
      _formError = null;
    });
    try {
      await widget.authRepository.login(
        username: _accountCtrl.text.trim(),
        password: _passwordCtrl.text.trim(),
      );
      TextInput.finishAutofillContext();
      // 认证状态机随 saveSession 切换，根路由 300ms fade 进主壳。
    } on ApiBusinessException catch (error) {
      if (!mounted) return;
      _showFormError(
        error.code == ApiCodes.badCredentials ? '用户名或密码错误' : '登录失败，请稍后重试',
      );
    } on ApiRateLimitException {
      if (!mounted) return;
      _showFormError('尝试次数过多，请稍后再试');
    } on ApiNetworkException {
      if (!mounted) return;
      _showNetworkSnackBar();
    } on SessionExpiredException {
      // 登录请求不带会话，理论不可达；静默留在登录页。
    } finally {
      if (mounted) setState(() => _submitting = false);
    }
  }

  void _goRegister() {
    Navigator.of(context).push(
      fadePageRoute<void>(RegisterPage(authRepository: widget.authRepository)),
    );
  }

  @override
  Widget build(BuildContext context) {
    return AuthScaffold(
      child: AutofillGroup(
        child: Column(
          // AuthScaffold 内禁用 Spacer，垂直居中用 mainAxisAlignment（§4 总则）。
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const SizedBox(height: 48),
            const BrandMark(),
            const SizedBox(height: 48),
            Focus(
              onFocusChange: (hasFocus) {
                if (!hasFocus) _validateAccountOnBlur();
              },
              child: AppTextField(
                label: '用户名 / 手机号',
                controller: _accountCtrl,
                prefixIcon: Icons.person_outline_rounded,
                errorText: _accountError,
                enabled: !_submitting,
                keyboardType: TextInputType.text,
                textInputAction: TextInputAction.next,
                autofillHints: const [AutofillHints.username],
                onChanged: (_) => _clearErrors(field: _Field.account),
              ),
            ),
            const SizedBox(height: 16),
            Focus(
              onFocusChange: (hasFocus) {
                if (!hasFocus) _validatePasswordOnBlur();
              },
              child: AppTextField(
                label: '密码',
                controller: _passwordCtrl,
                prefixIcon: Icons.lock_outline_rounded,
                obscurable: true,
                errorText: _passwordError,
                enabled: !_submitting,
                textInputAction: TextInputAction.done,
                autofillHints: const [AutofillHints.password],
                onChanged: (_) => _clearErrors(field: _Field.password),
                onSubmitted: (_) => _submit(),
              ),
            ),
            if (_formError != null) ...[
              const SizedBox(height: 16),
              InlineErrorBanner(message: _formError!),
            ],
            const SizedBox(height: 24),
            PrimaryButton(
              label: '登录',
              isLoading: _submitting,
              onPressed: _submit,
            ),
            const SizedBox(height: 16),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                const Text(
                  '还没有账号？',
                  style: TextStyle(color: AppColors.muted, fontSize: 14),
                ),
                TextButton(
                  style: TextButton.styleFrom(
                    foregroundColor: AppColors.primaryStrong,
                    minimumSize: const Size(44, 44),
                    padding: const EdgeInsets.symmetric(horizontal: 8),
                    textStyle: const TextStyle(
                      fontSize: 14,
                      fontWeight: FontWeight.w700,
                    ),
                  ),
                  onPressed: _submitting ? null : _goRegister,
                  child: const Text('立即注册'),
                ),
              ],
            ),
            const SizedBox(height: 24),
            // 协议行：v1 协议页未就绪，整行不渲染（组装稿 §5）。
            // 预留区（短信验证码/第三方登录）：不渲染任何占位（ADR-004）。
          ],
        ),
      ),
    );
  }
}