/*
 * Copyright (c) 2017, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 * WSO2 Inc. 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 org.wso2.carbon.stream.processor.core.ha;

import org.apache.log4j.Logger;
import org.wso2.siddhi.core.event.Event;
import org.wso2.siddhi.core.stream.output.sink.SinkHandler;
import org.wso2.siddhi.core.stream.output.sink.SinkHandlerCallback;
import org.wso2.siddhi.query.api.definition.StreamDefinition;

import java.util.Map;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * Implementation of {@link SinkHandler} used for 2 node minimum HA
 */
public class HACoordinationSinkHandler extends SinkHandler {
    private static final Logger log = Logger.getLogger(HACoordinationSinkHandler.class);

    private boolean isActiveNode;
    private boolean isForcePublishing;
    private long lastPublishedEventTimestamp = 0L;
    private Queue<Event> passiveNodeProcessedEvents;
    private String sinkHandlerElementId;
    private boolean isQueueFlushing;
    private final Object lockObject = new Object();
    private SinkHandlerCallback sinkHandlerCallBack;

    private static final String SINK = "sink";
    private static final String DISTRIBUTION = "distribution";
    private static final String FORCE_PUBLISH = "forcePublish";
    private static final String TRUE = "TRUE";

    private final int queueCapacity;

    /**
     * Constructor.
     *
     * @param queueCapacity is the size of the queue that would hold events in the Passive Node
     */
    public HACoordinationSinkHandler(int queueCapacity) {
        this.queueCapacity = queueCapacity;
        passiveNodeProcessedEvents = new LinkedBlockingQueue<>(queueCapacity);
    }

    @Override
    public void init(String sinkHandlerElementId, StreamDefinition streamDefinition,
                     SinkHandlerCallback sinkHandlerCallback) {
        this.sinkHandlerElementId = sinkHandlerElementId;
        this.sinkHandlerCallBack = sinkHandlerCallback;
        setForcePublishing(streamDefinition);
    }

    /**
     * Method that would publish events if this is the Active Node.
     * Will buffer all events if this is the Passive Node.
     *
     * @param event the event to be published.
     * @param sinkHandlerCallback callback that would publish events.
     */
    @Override
    public void handle(Event event, SinkHandlerCallback sinkHandlerCallback) {
        if (isActiveNode || isForcePublishing) {
            if (isQueueFlushing) {
                synchronized (lockObject) {
                    try {
                        lockObject.wait();
                    } catch (InterruptedException e) {
                        log.error("Error in waiting for buffered events to publish when changing from passive node " +
                                "to active node.", e);
                    }
                }
            }
            lastPublishedEventTimestamp = event.getTimestamp();
            sinkHandlerCallback.mapAndSend(event);
        } else {
            synchronized (this) {
                boolean eventBuffered = passiveNodeProcessedEvents.offer(event);
                if (!eventBuffered) { //Handles if the queue is full
                    passiveNodeProcessedEvents.remove();
                    passiveNodeProcessedEvents.add(event);
                }
            }
        }
    }

    /**
     * Method that would publish events if this is the Active Node.
     * Will buffer all events if this is the Passive Node.
     *
     * @param events the event array to be published.
     * @param sinkHandlerCallback callback that would publish events.
     */
    @Override
    public void handle(Event[] events, SinkHandlerCallback sinkHandlerCallback) {
        if (isActiveNode || isForcePublishing) {
            if (isQueueFlushing) {
                synchronized (lockObject) {
                    try {
                        lockObject.wait();
                    } catch (InterruptedException e) {
                        log.error("Error in waiting for buffered events to publish when changing from passive node " +
                                "to active node.", e);
                    }
                }
            }
            lastPublishedEventTimestamp = events[events.length - 1].getTimestamp();
            sinkHandlerCallback.mapAndSend(events);
        } else {
            synchronized (this) {
                int sizeAfterUpdate = passiveNodeProcessedEvents.size() + events.length;
                if (sizeAfterUpdate >= queueCapacity) {
                    for (int i = queueCapacity; i < sizeAfterUpdate; i++) {
                        passiveNodeProcessedEvents.remove();
                    }
                }
                for (Event event : events) {
                    passiveNodeProcessedEvents.add(event);
                }
            }
        }
    }

    /**
     * Method to change the sink handler to Active state so that publishing of events is commenced.
     * The currently buffered events will be published since it holds the events that the active node may not
     * have published yet. This might lead to event duplication but guarantees no events are dropped.
     * Will only be called when this node is the Passive Node.
     */
    public void setAsActive() {
        //When passive node becomes active, queued events should be published before any other events are processed
        this.isQueueFlushing = true;
        this.isActiveNode = true;
        Event event;
        while ((event = passiveNodeProcessedEvents.poll()) != null) {
            sinkHandlerCallBack.mapAndSend(event);
        }
        this.isQueueFlushing = false;
        synchronized (lockObject) {
            lockObject.notifyAll();
        }
    }

    /**
     * Get the timestamp of the last event published from the given sink.
     * Will only be called when this node is the Active node and publishing events.
     *
     * @return Object that holds the Sink Handler Element Id and timestamp of last published event.
     */
    public long getActiveNodeLastPublishedTimestamp() {
        //Since both nodes deploy same siddhi apps, every sink handler will get the same element Id in both nodes
        return lastPublishedEventTimestamp;
    }

    /**
     * Method that removes the events from the queue that the active node has already published
     *
     * @param activeLastPublishedTimestamp timestamp of the last event the active node published from the given sink
     */
    public void trimPassiveNodeEventQueue(long activeLastPublishedTimestamp) {
        while (passiveNodeProcessedEvents.peek() != null &&
                passiveNodeProcessedEvents.peek().getTimestamp() <= activeLastPublishedTimestamp) {
            passiveNodeProcessedEvents.remove();
        }
    }

    public Queue<Event> getPassiveNodeProcessedEvents() {
        return passiveNodeProcessedEvents;
    }

    @Override
    public Map<String, Object> currentState() {
        // Do Nothing
        return null;
    }

    @Override
    public void restoreState(Map<String, Object> map) {
        // Do Nothing
    }

    @Override
    public String getElementId() {
        return sinkHandlerElementId;
    }

    /**
     * Method that would enable force publishing data regardless of the Node's mode,
     * only when forcePublish is set to true
     *
     * @param streamDefinition the stream definition based on which, a sink is identified
     */
    private void setForcePublishing(StreamDefinition streamDefinition) {
        streamDefinition.getAnnotations().forEach(streamAnnotation -> {
            if (streamAnnotation.getName().equalsIgnoreCase(SINK)) {
                streamAnnotation.getAnnotations().forEach(sinkAnnotation -> {
                    if (sinkAnnotation.getName().equalsIgnoreCase(DISTRIBUTION)) {
                        sinkAnnotation.getElements().forEach(distributedSinkElement -> {
                            if (distributedSinkElement.getKey().equalsIgnoreCase(FORCE_PUBLISH)) {
                                this.isForcePublishing =
                                        distributedSinkElement.getValue().equalsIgnoreCase(TRUE);
                            }
                        });
                    }
                });
            }
        });
    }
}
