import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../data/ai/model_lifecycle.dart';
import '../../state/ai_providers.dart';

class SettingsScreen extends ConsumerWidget {
  const SettingsScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return Scaffold(
      appBar: AppBar(title: const Text('설정')),
      body: ListView(
        children: const [
          _SectionHeader('AI 도움'),
          _AiSection(),
        ],
      ),
    );
  }
}

class _SectionHeader extends StatelessWidget {
  final String title;
  const _SectionHeader(this.title);
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
      child: Text(
        title,
        style: Theme.of(context).textTheme.titleSmall,
      ),
    );
  }
}

class _AiSection extends ConsumerWidget {
  const _AiSection();

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final settings = ref.watch(aiSettingsProvider);
    final availability = ref.watch(modelAvailabilityProvider);
    final download = ref.watch(modelDownloadControllerProvider);
    final optIn = settings.maybeWhen(data: (v) => v, orElse: () => false);
    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        SwitchListTile(
          title: const Text('AI 도움 켜기'),
          subtitle: const Text(
            'Gemma 4 E2B 모델 ≈ 2.4GB. 모든 처리는 단말에서 일어납니다.',
          ),
          value: optIn,
          onChanged: (v) async {
            if (v) {
              final ok = await _confirmOptIn(context);
              if (ok != true) return;
            } else {
              final ok = await _confirmOptOut(context);
              if (ok != true) return;
            }
            final freed =
                await ref.read(aiSettingsControllerProvider).setOptIn(v);
            if (!context.mounted) return;
            if (!v && freed > 0) {
              ScaffoldMessenger.of(context).showSnackBar(
                SnackBar(content: Text('공간 확보됨 ${_fmtMB(freed)}')),
              );
            }
          },
        ),
        availability.when(
          loading: () => const ListTile(title: Text('상태 확인 중...')),
          error: (e, _) => ListTile(title: Text('상태 오류: $e')),
          data: (a) => ListTile(
            title: const Text('모델 상태'),
            subtitle: Text(_describe(a)),
          ),
        ),
        if (optIn && download != null)
          _DownloadProgressTile(progress: download, ref: ref),
        const Padding(
          padding: EdgeInsets.fromLTRB(16, 8, 16, 16),
          child: Text(
            '베타 기능 · 모델 다운로드가 정식 제공되기 전까지 일부 동작이 제한됩니다.',
            style: TextStyle(fontSize: 12, color: Colors.grey),
          ),
        ),
      ],
    );
  }

  String _describe(ModelAvailability a) {
    switch (a) {
      case ModelAvailability.ready:
        return '준비 완료 — 새 습관 만들기에서 ✨ AI 제안을 쓸 수 있어요';
      case ModelAvailability.missing:
        return '아직 받지 않았어요 — 위 토글을 켜면 다운로드합니다';
      case ModelAvailability.corrupt:
        return '파일이 손상됐어요 — 끄고 다시 켜면 새로 받습니다';
      case ModelAvailability.downloading:
        return '다운로드 중';
    }
  }

  String _fmtMB(int bytes) {
    final mb = bytes / (1024 * 1024);
    return '${mb.toStringAsFixed(1)} MB';
  }

  Future<bool?> _confirmOptIn(BuildContext context) {
    return showDialog<bool>(
      context: context,
      builder: (_) => AlertDialog(
        title: const Text('AI 도움 켜기'),
        content: Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: const [
            Text(
              '단말에서 동작하는 AI 모델을 내려받습니다.',
              style: TextStyle(fontWeight: FontWeight.w600),
            ),
            SizedBox(height: 12),
            _Bullet('파일 크기: 약 2.4GB'),
            _Bullet('WiFi 연결을 권장합니다'),
            _Bullet('모든 처리는 단말에서만 일어나며, 입력 텍스트는 외부로 전송되지 않습니다'),
            _Bullet('Gemma 이용약관(ai.google.dev/gemma/terms)에 동의합니다'),
          ],
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: const Text('취소'),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: const Text('동의하고 다운로드'),
          ),
        ],
      ),
    );
  }

  Future<bool?> _confirmOptOut(BuildContext context) {
    return showDialog<bool>(
      context: context,
      builder: (_) => AlertDialog(
        title: const Text('AI 도움 끄기'),
        content: Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: const [
            Text('모델 파일이 단말에서 삭제됩니다.'),
            SizedBox(height: 8),
            Text(
              '약 2.4GB 의 저장공간이 확보돼요.',
              style: TextStyle(fontSize: 13, color: Colors.grey),
            ),
            SizedBox(height: 4),
            Text(
              '다시 켜면 다시 다운로드해야 합니다.',
              style: TextStyle(fontSize: 13, color: Colors.grey),
            ),
          ],
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: const Text('취소'),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: const Text('끄고 삭제'),
          ),
        ],
      ),
    );
  }
}

class _Bullet extends StatelessWidget {
  final String text;
  const _Bullet(this.text);
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.only(bottom: 4),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          const Padding(
            padding: EdgeInsets.only(top: 6, right: 8),
            child: Icon(Icons.circle, size: 5),
          ),
          Expanded(child: Text(text, style: const TextStyle(fontSize: 14))),
        ],
      ),
    );
  }
}

/// AC2: shows download progress + pause/resume/restart controls.
class _DownloadProgressTile extends StatelessWidget {
  final DownloadProgress progress;
  final WidgetRef ref;
  const _DownloadProgressTile({required this.progress, required this.ref});

  @override
  Widget build(BuildContext context) {
    final scheme = Theme.of(context).colorScheme;
    final controller = ref.read(modelDownloadControllerProvider.notifier);
    final pct = progress.totalBytes > 0
        ? (progress.bytesReceived / progress.totalBytes).clamp(0.0, 1.0)
        : null;
    final pctText = pct != null
        ? '${(pct * 100).toStringAsFixed(0)}%'
        : '계산 중';
    final size =
        '${_fmtBytes(progress.bytesReceived)}'
        '${progress.totalBytes > 0 ? " / ${_fmtBytes(progress.totalBytes)}" : ""}';

    final (stateLabel, stateColor) = switch (progress.state) {
      DownloadState.downloading => ('다운로드 중', scheme.primary),
      DownloadState.paused => ('일시정지됨', scheme.outline),
      DownloadState.failed => ('실패', scheme.error),
      DownloadState.completed => ('준비 완료', Colors.green.shade700),
      DownloadState.idle => ('대기 중', scheme.outline),
    };

    Widget controls;
    switch (progress.state) {
      case DownloadState.downloading:
        controls = TextButton.icon(
          icon: const Icon(Icons.pause),
          label: const Text('일시정지'),
          onPressed: controller.pause,
        );
        break;
      case DownloadState.paused:
        controls = FilledButton.tonalIcon(
          icon: const Icon(Icons.play_arrow),
          label: const Text('재개'),
          onPressed: controller.resume,
        );
        break;
      case DownloadState.failed:
        controls = FilledButton.tonalIcon(
          icon: const Icon(Icons.refresh),
          label: const Text('다시 시도'),
          onPressed: controller.resume,
        );
        break;
      case DownloadState.completed:
      case DownloadState.idle:
        controls = const SizedBox.shrink();
        break;
    }

    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 0, 16, 12),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          Row(
            children: [
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text(
                      stateLabel,
                      style: TextStyle(
                        fontSize: 13,
                        fontWeight: FontWeight.w600,
                        color: stateColor,
                      ),
                    ),
                    const SizedBox(height: 2),
                    Text(
                      progress.state == DownloadState.completed
                          ? size
                          : '$size · $pctText',
                      style: TextStyle(
                        fontSize: 12,
                        color: scheme.onSurfaceVariant,
                      ),
                    ),
                  ],
                ),
              ),
              controls,
            ],
          ),
          const SizedBox(height: 6),
          ClipRRect(
            borderRadius: BorderRadius.circular(4),
            child: LinearProgressIndicator(
              value: pct,
              minHeight: 6,
            ),
          ),
          if (progress.state == DownloadState.failed)
            Padding(
              padding: const EdgeInsets.only(top: 6),
              child: Text(
                _friendlyError(progress.errorMessage),
                style: TextStyle(fontSize: 12, color: scheme.error),
              ),
            ),
        ],
      ),
    );
  }

  /// Maps internal error codes to user-friendly Korean messages.
  /// Hides technical detail (HTTP status, stack) — keeps the next action
  /// obvious instead.
  String _friendlyError(String? raw) {
    if (raw == null) return '다운로드에 실패했어요. 다시 시도해주세요.';
    if (raw.startsWith('network:')) {
      return '네트워크 연결을 확인하고 다시 시도해주세요.';
    }
    if (raw.startsWith('http ')) {
      return '서버 응답이 올바르지 않습니다. 잠시 후 다시 시도해주세요.';
    }
    if (raw.startsWith('stream:')) {
      return '다운로드가 중단되었어요. 다시 시도하면 이어받습니다.';
    }
    if (raw == 'sha mismatch') {
      return '파일이 손상되었어요. 다시 시도하면 처음부터 받습니다.';
    }
    return '다운로드에 실패했어요. 다시 시도해주세요.';
  }

  String _fmtBytes(int bytes) {
    if (bytes < 1024) return '$bytes B';
    if (bytes < 1024 * 1024) return '${(bytes / 1024).toStringAsFixed(1)} KB';
    if (bytes < 1024 * 1024 * 1024) {
      return '${(bytes / (1024 * 1024)).toStringAsFixed(1)} MB';
    }
    return '${(bytes / (1024 * 1024 * 1024)).toStringAsFixed(2)} GB';
  }
}