Connector.cs

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using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Client.Options;
using MQTTnet.Client.Disconnecting;
using MQTTnet.Client.Connecting;

using System.Text;

namespace MQttConnection
{
    public class Connector
    {
        private string _host;
        private int _port;
        private bool _tls = true;
        private string? _username;
        private string? _password;
        private string _payload;
        private string _topic;
        private string _clientid = "Client";
        public event MessageHandler messagehandler;
        public delegate void MessageHandler(Connector c, Message e);
        public static IMqttClient client = new MqttFactory().CreateMqttClient();

        public string Host { get { return _host; } set { _host = value; } }
        public int Port { get { return _port; } set { _port = value; } }
        public string Payload { get { return _payload; } set { _payload = value; } }
        public bool Tls { get { return _tls; } set { _tls = value; } }
        public string topic { get { return _topic; } set { _topic = value; } }
        public string clientid { get { return _clientid; } set { _clientid = value; } } 

       
        private static MqttClientOptionsBuilder mqttClientOptionsBuilder = new MqttClientOptionsBuilder();
        
        public Connector()
        {
            _host = "localhost";
            _port = 1883;
            _payload = "";
        }

        public Connector(string host, int port)
        {
            _host = host;
            _port = port;
            _payload = "";
        }

        public Connector(string host, int port, string username, string password)
        {
            _host = host;
            _port = port;
            _username = username;
            _password = password;
            _payload = "";
        }

        public async Task Initialize()
        {
            try
            {
                client.UseApplicationMessageReceivedHandler(MessageRecieved);
                client.UseConnectedHandler(ConnectionHandler);
                client.UseDisconnectedHandler(DisconnectHandler);

                var options = BuildClientOptions();
                await client.ConnectAsync(options, CancellationToken.None);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            
        }

        public async Task<bool> CloseConnection()
        {
            await client.DisconnectAsync();
            return true;
        }
       
        public async void UnsubscribeTopic(string topic)
        {
            await client.UnsubscribeAsync(topic);
            
        }

        public async void SubscribeTopic(string topic)
        {
           await client.SubscribeAsync(topic);   
        }

        public async Task PublishAsync(string topic, string payload, bool retainFlag = true, int qos = 1) =>
            await client.PublishAsync(new MqttApplicationMessageBuilder()
                .WithTopic(topic)
                .WithPayload(payload)
                .WithQualityOfServiceLevel((MQTTnet.Protocol.MqttQualityOfServiceLevel)qos)
                .WithRetainFlag(retainFlag)
                .Build());

        private void ConnectionHandler(MqttClientConnectedEventArgs e)
        {
            
            Message message = new ();
            message.EventMessage = e.ConnectResult.ResultCode.ToString();
            messagehandler(this, message);

        }

        private void DisconnectHandler(MqttClientDisconnectedEventArgs e)
        {
            Message message = new ();
            message.EventMessage = e.Exception.Message;
            messagehandler(this, message);
        }

        private void MessageRecieved(MqttApplicationMessageReceivedEventArgs mq_message)
        {
            Payload = Encoding.UTF8.GetString(mq_message.ApplicationMessage.Payload);
            
            Message message = new ();
            message.EventMessage = Payload;
            messagehandler(this, message);
        }

        private IMqttClientOptions BuildClientOptions()
        {
            if (_host == null || _port == 0)
            {
                throw new ArgumentException("No Host or Port");
            }
            mqttClientOptionsBuilder.WithClientId(_clientid);
            mqttClientOptionsBuilder.WithTcpServer(_host, _port);
            mqttClientOptionsBuilder.WithCleanSession();
            if (_username != null && _password != null)
            {
                mqttClientOptionsBuilder.WithCredentials(_username, _password);
            }
            if (_tls)
            {
                mqttClientOptionsBuilder.WithTls();
            }

            var options = mqttClientOptionsBuilder.Build();
            return options;
        }

    }
}