/*
 * Copyright (c) 2018 - 2023, Entgra (Pvt) Ltd. (http://www.entgra.io) All Rights Reserved.
 *
 * Entgra (Pvt) Ltd. licenses this file to you under the Apache License,
 * Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package io.entgra.device.mgt.plugins.virtualfirealarm.agent.transport.mqtt;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttSecurityException;
import io.entgra.device.mgt.plugins.virtualfirealarm.agent.transport.TransportHandler;
import io.entgra.device.mgt.plugins.virtualfirealarm.agent.transport.TransportHandlerException;

import java.io.File;
import java.nio.charset.StandardCharsets;

/**
 * This is an abstract class that implements the "TransportHandler" interface. The interface is an abstraction for
 * the core functionality with regards to device-server communication regardless of the Transport protocol. This
 * specific class contains the HTTP-Transport specific implementations. The class implements utility methods for the
 * case of a HTTP communication. However, this "abstract class", even-though it implements the "TransportHandler"
 * interface, does not contain the logic relevant to the interface methods. The specific functionality of the
 * interface methods are intended to be implemented by the concrete class that extends this abstract class and
 * utilizes the HTTP specific functionality (ideally a device API writer who would like to communicate to the device
 * via HTTP Protocol).
 * <p/>
 * This class contains the Device-Management specific implementation for all the MQTT functionality. This includes
 * connecting to a MQTT Broker & subscribing to the appropriate MQTT-topic, action plan upon losing connection or
 * successfully delivering a message to the broker and processing incoming messages. Makes use of the 'Paho-MQTT'
 * library provided by Eclipse Org.
 */
public abstract class MQTTTransportHandler
        implements MqttCallback, TransportHandler<MqttMessage> {
    private static final Log log = LogFactory.getLog(MQTTTransportHandler.class);
    public static final int DEFAULT_MQTT_QUALITY_OF_SERVICE = 0;

    private MqttClient client;
    private String clientId;
    private MqttConnectOptions options;
    private String clientWillTopic;

    protected String mqttBrokerEndPoint;
    protected int timeoutInterval;
    protected String subscribeTopic;

    /**
     * Constructor for the MQTTTransportHandler which takes in the owner, type of the device
     * and the MQTT Broker URL and the topic to subscribe.
     *
     * @param deviceOwner        the owner of the device.
     * @param deviceType         the CDMF Device-Type of the device.
     * @param mqttBrokerEndPoint the IP/URL of the MQTT broker endpoint.
     * @param subscribeTopic     the MQTT topic to which the client is to be subscribed
     */
    protected MQTTTransportHandler(String deviceOwner, String deviceType,
                                   String mqttBrokerEndPoint,
                                   String subscribeTopic) {
        this.clientId = deviceOwner + ":" + deviceType;
        this.subscribeTopic = subscribeTopic;
        this.clientWillTopic = deviceType + File.separator + "disconnection";
        this.mqttBrokerEndPoint = mqttBrokerEndPoint;
        this.timeoutInterval = DEFAULT_TIMEOUT_INTERVAL;
        this.initSubscriber();
    }

    /**
     * Constructor for the MQTTTransportHandler which takes in the owner, type of the device
     * and the MQTT Broker URL and the topic to subscribe. Additionally this constructor takes in
     * the reconnection-time interval between successive attempts to connect to the broker.
     *
     * @param deviceOwner        the owner of the device.
     * @param deviceType         the CDMF Device-Type of the device.
     * @param mqttBrokerEndPoint the IP/URL of the MQTT broker endpoint.
     * @param subscribeTopic     the MQTT topic to which the client is to be subscribed
     * @param intervalInMillis   the time interval in MILLI-SECONDS between successive
     *                           attempts to connect to the broker.
     */
    protected MQTTTransportHandler(String deviceOwner, String deviceType,
                                   String mqttBrokerEndPoint, String subscribeTopic,
                                   int intervalInMillis) {
        this.clientId = deviceOwner + ":" + deviceType;
        this.subscribeTopic = subscribeTopic;
        //TODO:: Use constant strings
        this.clientWillTopic = deviceType + File.separator + "disconnection";
        this.mqttBrokerEndPoint = mqttBrokerEndPoint;
        this.timeoutInterval = intervalInMillis;
        this.initSubscriber();
    }

    public void setTimeoutInterval(int timeoutInterval) {
        this.timeoutInterval = timeoutInterval;
    }

    /**
     * Initializes the MQTT-Client. Creates a client using the given MQTT-broker endpoint and the
     * clientId (which is constructed by a concatenation of [deviceOwner]:[deviceType]). Also sets
     * the client's options parameter with the clientWillTopic (in-case of connection failure) and
     * other info. Also sets the call-back this current class.
     */
    private void initSubscriber() {
        try {
            client = new MqttClient(this.mqttBrokerEndPoint, clientId, null);
            //TODO:: Need to check for debug
            log.info("MQTT subscriber was created with ClientID : " + clientId);
        } catch (MqttException ex) {
            //TODO:: Remove unnecessary formatting and print exception
            String errorMsg = "MQTT Client Error\n" + "\tReason:  " + ex.getReasonCode() +
                    "\n\tMessage: " + ex.getMessage() + "\n\tLocalMsg: " +
                    ex.getLocalizedMessage() + "\n\tCause: " + ex.getCause() +
                    "\n\tException: " + ex;
            log.error(errorMsg);
            //TODO:: Throw the error out
        }

        options = new MqttConnectOptions();
        options.setCleanSession(false);
        //TODO:: Use constant strings
        options.setWill(clientWillTopic, "Connection-Lost".getBytes(StandardCharsets.UTF_8), 2,
                        true);
        client.setCallback(this);
    }

    /**
     * Checks whether the connection to the MQTT-Broker persists.
     *
     * @return true if the client is connected to the MQTT-Broker, else false.
     */
    @Override
    public boolean isConnected() {
        return client.isConnected();
    }


    protected void connectToQueue(String username, String password) throws TransportHandlerException {
        options.setUserName(username);
        options.setPassword(password.toCharArray());
        connectToQueue();
    }

    /**
     * Connects to the MQTT-Broker and if successfully established connection.
     *
     * @throws TransportHandlerException in the event of 'Connecting to' the MQTT broker fails.
     */
    protected void connectToQueue() throws TransportHandlerException {
        try {
            client.connect(options);

            if (log.isDebugEnabled()) {
                log.debug("Subscriber connected to queue at: " + this.mqttBrokerEndPoint);
            }
        } catch (MqttSecurityException ex) {
            String errorMsg = "MQTT Security Exception when connecting to queue\n" + "\tReason: " +
                    " " +
                    ex.getReasonCode() + "\n\tMessage: " + ex.getMessage() +
                    "\n\tLocalMsg: " + ex.getLocalizedMessage() + "\n\tCause: " +
                    ex.getCause() + "\n\tException: " + ex;
            //TODO:: Compulsory log of errors and remove formatted error
            if (log.isDebugEnabled()) {
                log.debug(errorMsg);
            }
            throw new TransportHandlerException(errorMsg, ex);

        } catch (MqttException ex) {
            //TODO:: Compulsory log of errors and remove formatted error
            String errorMsg = "MQTT Exception when connecting to queue\n" + "\tReason:  " +
                    ex.getReasonCode() + "\n\tMessage: " + ex.getMessage() +
                    "\n\tLocalMsg: " + ex.getLocalizedMessage() + "\n\tCause: " +
                    ex.getCause() + "\n\tException: " + ex;
            if (log.isDebugEnabled()) {
                log.debug(errorMsg);
            }
            throw new TransportHandlerException(errorMsg, ex);
        }
    }

    /**
     * Subscribes to the MQTT-Topic specific to this MQTT Client. (The MQTT-Topic specific to the
     * device is taken in as a constructor parameter of this class) .
     *
     * @throws TransportHandlerException in the event of 'Subscribing to' the MQTT broker
     *                                   fails.
     */
    protected void subscribeToQueue() throws TransportHandlerException {
        try {
            //TODO:: QoS Level take it from a variable
            client.subscribe(subscribeTopic, 0);
            log.info("Subscriber '" + clientId + "' subscribed to topic: " + subscribeTopic);
        } catch (MqttException ex) {
            //TODO:: Compulsory log of errors and remove formatted error
            String errorMsg = "MQTT Exception when trying to subscribe to topic: " +
                    subscribeTopic + "\n\tReason:  " + ex.getReasonCode() +
                    "\n\tMessage: " + ex.getMessage() + "\n\tLocalMsg: " +
                    ex.getLocalizedMessage() + "\n\tCause: " + ex.getCause() +
                    "\n\tException: " + ex;
            if (log.isDebugEnabled()) {
                log.debug(errorMsg);
            }

            throw new TransportHandlerException(errorMsg, ex);
        }
    }


    /**
     * This method is used to publish reply-messages for the control signals received.
     * Invocation of this method calls its overloaded-method with a QoS equal to that of the
     * default value.
     *
     * @param topic   the topic to which the reply message is to be published.
     * @param payLoad the reply-message (payload) of the MQTT publish action.
     */
    protected void publishToQueue(String topic, String payLoad)
            throws TransportHandlerException {
        publishToQueue(topic, payLoad, DEFAULT_MQTT_QUALITY_OF_SERVICE, false);
    }

    /**
     * This is an overloaded method that publishes MQTT reply-messages for control signals
     * received form the IoT-Server.
     *
     * @param topic   the topic to which the reply message is to be published
     * @param payLoad the reply-message (payload) of the MQTT publish action.
     * @param qos     the Quality-of-Service of the current publish action.
     *                Could be 0(At-most once), 1(At-least once) or 2(Exactly once)
     */
    protected void publishToQueue(String topic, String payLoad, int qos, boolean retained)
            throws TransportHandlerException {
        try {
            client.publish(topic, payLoad.getBytes(StandardCharsets.UTF_8), qos, retained);
            if (log.isDebugEnabled()) {
                log.debug("Message: " + payLoad + " to MQTT topic [" + topic + "] published successfully");
            }
        } catch (MqttException ex) {
            String errorMsg =
                    "MQTT Client Error" + "\n\tReason:  " + ex.getReasonCode() + "\n\tMessage: " +
                            ex.getMessage() + "\n\tLocalMsg: " + ex.getLocalizedMessage() +
                            "\n\tCause: " + ex.getCause() + "\n\tException: " + ex;
            log.info(errorMsg);
            throw new TransportHandlerException(errorMsg, ex);
        }
    }


    protected void publishToQueue(String topic, MqttMessage message)
            throws TransportHandlerException {
        try {
            client.publish(topic, message);
            if (log.isDebugEnabled()) {
                log.debug("Message: " + message.toString() + " to MQTT topic [" + topic + "] published successfully");
            }
        } catch (MqttException ex) {
            //TODO:: Compulsory log of errors and remove formatted error
            String errorMsg =
                    "MQTT Client Error" + "\n\tReason:  " + ex.getReasonCode() + "\n\tMessage: " +
                            ex.getMessage() + "\n\tLocalMsg: " + ex.getLocalizedMessage() +
                            "\n\tCause: " + ex.getCause() + "\n\tException: " + ex;
            log.info(errorMsg);
            throw new TransportHandlerException(errorMsg, ex);
        }
    }


    /**
     * Callback method which is triggered once the MQTT client losers its connection to the broker.
     * Spawns a new thread that executes necessary actions to try and reconnect to the endpoint.
     *
     * @param throwable a Throwable Object containing the details as to why the failure occurred.
     */
    @Override
    public void connectionLost(Throwable throwable) {
        log.warn("Lost Connection for client: " + this.clientId +
                         " to " + this.mqttBrokerEndPoint + ".\nThis was due to - " + throwable.getMessage());

        Thread reconnectThread = new Thread() {
            public void run() {
                connect();
            }
        };
        reconnectThread.start();
    }

    /**
     * Callback method which is triggered upon receiving a MQTT Message from the broker. Spawns a
     * new thread that executes any actions to be taken with the received message.
     *
     * @param topic       the MQTT-Topic to which the received message was published to and the
     *                    client was subscribed to.
     * @param mqttMessage the actual MQTT-Message that was received from the broker.
     */
    @Override
    public void messageArrived(final String topic, final MqttMessage mqttMessage) {
        if (log.isDebugEnabled()) {
            log.info("Got an MQTT message '" + mqttMessage.toString() + "' for topic '" + topic + "'.");
        }

        Thread messageProcessorThread = new Thread() {
            public void run() {
                processIncomingMessage(mqttMessage, topic);
            }
        };
        messageProcessorThread.setDaemon(true);
        messageProcessorThread.start();
    }

    /**
     * Callback method which gets triggered upon successful completion of a message delivery to
     * the broker.
     *
     * @param iMqttDeliveryToken the MQTT-DeliveryToken which includes the details about the
     *                           specific message delivery.
     */
    @Override
    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        String message = "";
        try {
            message = iMqttDeliveryToken.getMessage().toString();
        } catch (MqttException e) {
            //TODO:: Throw errors
            log.error(
                    "Error occurred whilst trying to read the message from the MQTT delivery token.");
        }
        String topic = iMqttDeliveryToken.getTopics()[0];
        String client = iMqttDeliveryToken.getClient().getClientId();

        if (log.isDebugEnabled()) {
            log.debug("Message - '" + message + "' of client [" + client + "] for the topic (" +
                              topic + ") was delivered successfully.");
        }
    }

    /**
     * Closes the connection to the MQTT Broker.
     */
    public void closeConnection() throws MqttException {
        if (client != null && isConnected()) {
            client.disconnect();
        }
    }
}

