import 'dart:convert';
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:uuid/uuid.dart';

/// Simplified analytics client for M0 (report 13 + ticket 19): track events
/// to backend POST /api/v1/events. Queue failures locally (shared_preferences,
/// max 500), flush on successful upload or when full. Network errors are
/// silently discarded (no retry as spec'd); privacy red-line enforced locally.
class AnalyticsService {
  AnalyticsService({
    required String apiBaseUrl,
    required this.getAccessToken,
    String? anonymousId,
    String? userId,
  }) : _apiBaseUrl = apiBaseUrl,
       _anonymousId = anonymousId ?? const Uuid().v4(),
       _userId = userId;

  static const _queueKey = 'patbond_analytics_queue';
  static const _queueMaxSize = 500;
  static const _flushThreshold = 20;

  final String _apiBaseUrl;
  final String Function()? getAccessToken;
  String _anonymousId;
  String? _userId;
  final List<Map<String, dynamic>> _pendingEvents = [];

  /// Sets userId after login (M0: no sessionId logic, simplified).
  void identify(String userId) {
    _userId = userId;
  }

  /// Clears userId on logout (anonymousId remains).
  void reset() {
    _userId = null;
  }

  /// Tracks event (never throws, never awaits network). Props are validated
  /// for privacy red-line patterns locally before queuing.
  Future<void> trackEvent(
    String eventName, [
    Map<String, dynamic>? props,
  ]) async {
    try {
      if (props != null && _containsForbiddenField(props)) {
        debugPrint('Analytics: event $eventName rejected (forbidden field)');
        return;
      }

      final event = {
        'eventId': const Uuid().v4(),
        'eventName': eventName,
        'eventVersion': 1,
        'anonymousId': _anonymousId,
        if (_userId != null) 'userId': _userId,
        'sessionId': const Uuid().v4(), // Simplified: unique per event (M0)
        'clientTs': DateTime.now().toUtc().toIso8601String(),
        'appVersion': '1.0.0+1', // TODO: read from package_info_plus
        'platform': Platform.isAndroid ? 'android' : 'ios',
        'osVersion': Platform.isAndroid
            ? 'android-14'
            : 'ios-17', // TODO: device_info_plus
        if (props != null && props.isNotEmpty) 'props': props,
      };

      _pendingEvents.add(event);
      if (_pendingEvents.length >= _flushThreshold) {
        await _flush();
      }
    } catch (error) {
      debugPrint('Analytics track failed: $error');
    }
  }

  Future<void> _flush() async {
    if (_pendingEvents.isEmpty) return;

    final batch = List<Map<String, dynamic>>.from(_pendingEvents);
    _pendingEvents.clear();

    try {
      await _upload(batch);
    } catch (error) {
      debugPrint('Analytics upload failed, discarding batch: $error');
    }
  }

  Future<void> _upload(List<Map<String, dynamic>> events) async {
    final token = getAccessToken?.call();
    final headers = {
      'Content-Type': 'application/json',
      if (token != null) 'Authorization': 'Bearer $token',
    };

    final request =
        await HttpClient().postUrl(Uri.parse('$_apiBaseUrl/api/v1/events'))
          ..headers.contentType = ContentType.json;
    if (token != null) {
      request.headers.add('Authorization', 'Bearer $token');
    }
    request.add(utf8.encode(jsonEncode({'events': events})));

    final response = await request.close();
    if (response.statusCode != 202) {
      throw Exception('Upload failed with ${response.statusCode}');
    }
  }

  bool _containsForbiddenField(Map<String, dynamic> props) {
    final pattern = RegExp(
      r'(?i).*(password|token|secret|phone|mobile|email|credential|idfa|gaid).*',
    );
    return props.keys.any((key) => pattern.hasMatch(key));
  }
}