import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
import '../core/network/api_config.dart';

/// Singleton service that manages TTS generation in the background.
/// Survives page navigation — when user leaves and comes back,
/// generation continues and result is available.
class TTSService extends ChangeNotifier {
  TTSService._();
  static final TTSService instance = TTSService._();

  Future<String?> _getToken() async {
    final prefs = await SharedPreferences.getInstance();
    return prefs.getString('access_token');
  }

  // ── Current task state ──
  bool _isGenerating = false;
  double _progress = 0.0; // 0.0 ~ 1.0
  String _statusMessage = '';
  String? _currentStoryTitle; // Which story is being generated

  // ── Result ──
  String? _audioUrl;
  String? _completedStoryTitle; // Which story the audio belongs to
  bool _justCompleted = false; // Flash animation trigger

  // ── Error ──
  String? _error;
  String? _errorTitle; // Which story the error belongs to

  // ── Getters ──
  bool get isGenerating => _isGenerating;
  double get progress => _progress;
  String get statusMessage => _statusMessage;
  String? get currentStoryTitle => _currentStoryTitle;
  String? get audioUrl => _audioUrl;
  String? get completedStoryTitle => _completedStoryTitle;
  bool get justCompleted => _justCompleted;
  String? get error => _error;
  String? get errorTitle => _errorTitle;

  /// Check if audio is ready for a specific story.
  bool hasAudioFor(String title) {
    return _completedStoryTitle == title && _audioUrl != null;
  }

  /// Check if currently generating for a specific story.
  bool isGeneratingFor(String title) {
    return _isGenerating && _currentStoryTitle == title;
  }

  /// Clear the "just completed" flag (after flash animation plays).
  void clearJustCompleted() {
    _justCompleted = false;
    notifyListeners();
  }

  /// Set audio URL directly (e.g. from pre-check).
  void setExistingAudio(String title, String url) {
    _completedStoryTitle = title;
    _audioUrl = url;
    _justCompleted = false;
    notifyListeners();
  }

  /// Check server for existing audio file by story ID.
  Future<void> checkExistingAudio(String title, {int? storyId}) async {
    if (title.isEmpty || storyId == null) return;
    try {
      final token = await _getToken();
      final resp = await http.get(
        Uri.parse('${ApiConfig.fullBaseUrl}/stories/$storyId/tts/'),
        headers: {
          if (token != null) 'Authorization': 'Bearer $token',
        },
      );
      if (resp.statusCode == 200) {
        final body = jsonDecode(resp.body);
        final data = body['data'];
        if (data != null && data['exists'] == true && data['audio_url'] != null) {
          _completedStoryTitle = title;
          _audioUrl = data['audio_url'] as String;
          notifyListeners();
        }
      }
    } catch (_) {}
  }

  /// Start TTS generation. Safe to call even if page navigates away.
  /// [storyId] is required to call the Django backend TTS endpoint.
  Future<void> generate({
    required String title,
    required String content,
    required int storyId,
  }) async {
    if (_isGenerating) return;

    _isGenerating = true;
    _progress = 0.0;
    _statusMessage = '正在连接...';
    _currentStoryTitle = title;
    _audioUrl = null;
    _completedStoryTitle = null;
    _justCompleted = false;
    _error = null;
    notifyListeners();

    try {
      final token = await _getToken();
      final client = http.Client();
      final request = http.Request(
        'POST',
        Uri.parse('${ApiConfig.fullBaseUrl}/stories/$storyId/tts/'),
      );
      request.headers['Content-Type'] = 'application/json';
      if (token != null) {
        request.headers['Authorization'] = 'Bearer $token';
      }

      final streamed = await client.send(request);

      String buffer = '';
      await for (final chunk in streamed.stream.transform(utf8.decoder)) {
        buffer += chunk;

        while (buffer.contains('\n\n')) {
          final idx = buffer.indexOf('\n\n');
          final block = buffer.substring(0, idx).trim();
          buffer = buffer.substring(idx + 2);

          String? jsonStr;
          for (final line in block.split('\n')) {
            if (line.startsWith('data: ')) {
              jsonStr = line.substring(6);
              break;
            }
          }
          if (jsonStr == null) continue;

          try {
            final data = jsonDecode(jsonStr);
            final stage = data['stage'] as String? ?? '';
            final message = data['message'] as String? ?? '';

            switch (stage) {
              case 'connecting':
                _updateProgress(0.10, '正在连接...');
                break;
              case 'generating':
                _updateProgress(0.30, '语音生成中...');
                break;
              case 'saving':
                _updateProgress(0.88, '正在保存...');
                break;
              case 'done':
                if (data['audio_url'] != null) {
                  _audioUrl = data['audio_url'] as String;
                  _completedStoryTitle = title;
                  _justCompleted = true;
                  _updateProgress(1.0, '生成完成');
                }
                break;
              case 'error':
                throw Exception(message);
              default:
                if (_progress < 0.85) {
                  _updateProgress(_progress + 0.02, message);
                }
            }
          } catch (e) {
            if (e is Exception &&
                e.toString().contains('语音合成失败')) {
              rethrow;
            }
          }
        }
      }

      client.close();

      _isGenerating = false;
      if (_audioUrl == null) {
        _error = '未获取到音频';
        _errorTitle = title;
        _statusMessage = '生成失败';
      }
      notifyListeners();
    } catch (e) {
      debugPrint('TTS generation error: $e');
      _isGenerating = false;
      _progress = 0.0;
      _error = e.toString();
      _errorTitle = title;
      _statusMessage = '生成失败';
      _justCompleted = false;
      notifyListeners();
    }
  }

  void _updateProgress(double progress, String message) {
    _progress = progress.clamp(0.0, 1.0);
    _statusMessage = message;
    notifyListeners();
  }

  /// Reset all state (e.g. when switching stories).
  void reset() {
    if (_isGenerating) return; // Don't reset during generation
    _progress = 0.0;
    _statusMessage = '';
    _currentStoryTitle = null;
    _audioUrl = null;
    _completedStoryTitle = null;
    _justCompleted = false;
    _error = null;
    _errorTitle = null;
    notifyListeners();
  }
}