fanuzu/app/lib/features/auth/login_screen.dart

import 'package:flutter/material.dart';

import '../../core/firebase/firebase_boot.dart';
import '../../core/theme/tokens.dart';
import 'auth.dart';
import 'auth_repository.dart';

/// S-A-LOGIN 로그인.
///
/// 시안: `시안/screens/S-A-LOGIN.html` · 명세: `wireframe/planning/screen-spec/onboard/S-A-LOGIN.md`
/// 골격 범위라 4개 버튼과 결과 안내까지만 구현했다. 약관 동의(S-A-TERMS) 이후 동선은 3주차다.
class LoginScreen extends StatefulWidget {
  const LoginScreen({super.key, required this.auth});

  final AuthRepository auth;

  @override
  State<LoginScreen> createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  String? _notice;
  bool _busy = false;

  Future<void> _signIn(SocialProvider provider) async {
    setState(() => _busy = true);
    final outcome = await widget.auth.signIn(provider);
    if (!mounted) return;
    setState(() {
      _busy = false;
      _notice = switch (outcome) {
        AuthSucceeded() => null,
        AuthCancelled() => null,
        AuthFailed(:final code, :final message) => '[$code] $message',
        AuthNotConfigured(:final provider, :final missing) =>
          '${provider.label.replaceAll('로 시작하기', '')} 로그인은 아직 준비 중입니다.\n'
              '필요한 항목: ${missing.join(' · ')}',
      };
    });
  }

  @override
  Widget build(BuildContext context) {
    final text = Theme.of(context).textTheme;
    return Scaffold(
      body: SafeArea(
        child: SingleChildScrollView(
          padding: const EdgeInsets.all(AppSpace.s5),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              const SizedBox(height: AppSpace.s6),
              // 로고 원본은 미확정(Q6)이라 워드마크를 텍스트로 둔다. 확정되면 이미지로 교체.
              Text('Fancake', style: text.displayMedium),
              const SizedBox(height: AppSpace.s4),
              Text('당신의 팬 활동을\n하나의 행성으로', style: text.displayLarge),
              const SizedBox(height: AppSpace.s4),
              Text(
                '로그인하면 이용약관과 개인정보 처리방침에 동의하는 절차로 이동합니다.',
                style: text.bodyMedium?.copyWith(color: AppColors.onCosmicVariant),
              ),
              const SizedBox(height: AppSpace.s7),
              Text('계정으로 시작하기', style: text.titleLarge),
              const SizedBox(height: AppSpace.s2),
              Text(
                '사용 중인 계정 하나를 선택해 주세요.',
                style: text.bodySmall,
              ),
              const SizedBox(height: AppSpace.s4),
              for (final p in widget.auth.providers) ...[
                _ProviderButton(
                  provider: p.provider,
                  enabled: !_busy,
                  onPressed: () => _signIn(p.provider),
                ),
                const SizedBox(height: AppSpace.s3),
              ],
              if (_notice != null) ...[
                const SizedBox(height: AppSpace.s2),
                _Notice(_notice!),
              ],
              if (widget.auth.isMockSessionAvailable) ...[
                const SizedBox(height: AppSpace.s5),
                const Divider(),
                const SizedBox(height: AppSpace.s4),
                _MockBanner(onEnter: widget.auth.signInWithMockSession),
              ],
              const SizedBox(height: AppSpace.s6),
            ],
          ),
        ),
      ),
    );
  }
}

/// 소셜 버튼. 색과 라벨은 각 사 브랜드 가이드 고정값이라 테마를 타지 않는다.
class _ProviderButton extends StatelessWidget {
  const _ProviderButton({
    required this.provider,
    required this.enabled,
    required this.onPressed,
  });

  final SocialProvider provider;
  final bool enabled;
  final VoidCallback onPressed;

  @override
  Widget build(BuildContext context) {
    final (fill, label, stroke) = switch (provider) {
      SocialProvider.kakao => (BrandColors.kakao, BrandColors.kakaoLabel, null),
      SocialProvider.naver => (BrandColors.naver, BrandColors.naverLabel, null),
      SocialProvider.apple => (
        BrandColors.apple,
        BrandColors.appleLabel,
        BrandColors.appleOnlight,
      ),
      SocialProvider.google => (
        BrandColors.googleFill,
        BrandColors.googleLabel,
        BrandColors.googleStroke,
      ),
    };
    return FilledButton(
      onPressed: enabled ? onPressed : null,
      style: FilledButton.styleFrom(
        backgroundColor: fill,
        foregroundColor: label,
        disabledBackgroundColor: fill.withValues(alpha: 0.4),
        side: stroke == null ? null : BorderSide(color: stroke),
      ),
      child: Text(provider.label),
    );
  }
}

class _Notice extends StatelessWidget {
  const _Notice(this.message);

  final String message;

  @override
  Widget build(BuildContext context) => Container(
    padding: const EdgeInsets.all(AppSpace.s4),
    decoration: BoxDecoration(
      color: AppColors.cosmicSurfaceContainer,
      border: Border.all(color: AppColors.cosmicOutline),
      borderRadius: BorderRadius.circular(AppRadius.md),
    ),
    child: Text(message, style: Theme.of(context).textTheme.bodySmall),
  );
}

/// Firebase 미설정 안내 + 탭 이동 시연 입구.
class _MockBanner extends StatelessWidget {
  const _MockBanner({required this.onEnter});

  final VoidCallback onEnter;

  @override
  Widget build(BuildContext context) {
    final text = Theme.of(context).textTheme;
    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        Text('목(mock) 모드', style: text.labelMedium),
        const SizedBox(height: AppSpace.s2),
        Text(FirebaseBoot.reason, style: text.bodySmall),
        const SizedBox(height: AppSpace.s3),
        OutlinedButton(
          onPressed: onEnter,
          child: const Text('목 세션으로 탭 둘러보기'),
        ),
      ],
    );
  }
}