import 'dart:convert';

import 'package:flutter/foundation.dart';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';

import 'mqtt_service.dart';

/// A single trace entry capturing a message-handling event.
class TraceEntry {
  final DateTime timestamp;
  final String event;
  final String details;

  const TraceEntry({
    required this.timestamp,
    required this.event,
    required this.details,
  });

  @override
  String toString() =>
      '[${timestamp.toIso8601String().substring(11, 23)}] $event — $details';
}

/// Singleton ring-buffer trace service.
///
/// Captures message-handling events from MQTT, chat screen, and other
/// components. The buffer is capped at [maxEntries] (default 200).
/// Works in both debug and release builds.
///
/// When an MqttService is attached via [attachMqtt], trace entries are
/// automatically published to the server on `pailot/control/in` so they
/// can be read from the daemon log.
class TraceService {
  TraceService._();
  static final TraceService instance = TraceService._();

  static const int maxEntries = 200;
  final List<TraceEntry> _entries = [];
  MqttService? _mqtt;

  /// Attach an MQTT service for auto-publishing traces to the server.
  void attachMqtt(MqttService mqtt) {
    _mqtt = mqtt;
  }

  /// All entries, oldest first.
  List<TraceEntry> get entries => List.unmodifiable(_entries);

  /// Add a trace entry. Oldest entry is evicted once the buffer is full.
  /// If MQTT is attached and connected, the entry is also published to the server.
  void addTrace(String event, String details) {
    _entries.add(TraceEntry(
      timestamp: DateTime.now(),
      event: event,
      details: details,
    ));
    if (_entries.length > maxEntries) {
      _entries.removeAt(0);
    }
    debugPrint('[TRACE] $event — $details');

    // Auto-publish to server if MQTT is connected
    _publishTrace(event, details);
  }

  void _publishTrace(String event, String details) {
    final mqtt = _mqtt;
    if (mqtt == null || !mqtt.isConnected) return;
    try {
      final payload = jsonEncode({
        'type': 'command',
        'command': 'app_trace',
        'event': event,
        'details': details,
        'ts': DateTime.now().millisecondsSinceEpoch,
      });
      final builder = MqttClientPayloadBuilder();
      builder.addString(payload);
      mqtt.publishRaw('pailot/control/in', builder.payload!, MqttQos.atMostOnce);
    } catch (_) {
      // Non-fatal — don't let trace logging break the app
    }
  }

  /// Clear all entries.
  void clear() => _entries.clear();
}