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package com.tinkerpop.gremlin.driver;

import com.tinkerpop.gremlin.driver.message.ResponseMessage;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
 * A queue of incoming {@link ResponseMessage} objects.  The queue is updated by the
 * {@link com.tinkerpop.gremlin.driver.Handler.GremlinResponseHandler} until a response terminator is identified.  At that point the fetch
 * status is changed to {@link Status#COMPLETE} and all results have made it client side.
 *
 * @author Stephen Mallette (http://stephen.genoprime.com)
 */
class ResponseQueue {
    public enum Status {
        FETCHING,
        COMPLETE
    }

    private final LinkedBlockingQueue responseQueue;

    private volatile Status status = Status.FETCHING;

    private final AtomicReference error = new AtomicReference<>();

    private final CompletableFuture readComplete;

    public ResponseQueue(final LinkedBlockingQueue responseQueue, final CompletableFuture readComplete) {
        this.responseQueue = responseQueue;
        this.readComplete = readComplete;
    }

    public void add(final ResponseMessage msg) {
        this.responseQueue.offer(msg);
    }

    public int size() {
        if (error.get() != null) throw new RuntimeException(error.get());
        return this.responseQueue.size();
    }

    public boolean isEmpty() {
        if (error.get() != null) throw new RuntimeException(error.get());
        return this.size() == 0;
    }

    public ResponseMessage poll() {
        ResponseMessage msg = null;
        do {
            if (error.get() != null) throw new RuntimeException(error.get());
            try {
                msg = responseQueue.poll(10, TimeUnit.MILLISECONDS);
            } catch (InterruptedException ie) {
                error.set(new RuntimeException(ie));
            }
        } while (null == msg && status == Status.FETCHING);

        if (error.get() != null) throw new RuntimeException(error.get());

        return msg;
    }

    public Status getStatus() {
        return status;
    }

    void markComplete() {
        this.status = Status.COMPLETE;
        this.readComplete.complete(null);
    }

    void markError(final Throwable throwable) {
        error.set(throwable);
        this.readComplete.complete(null);
    }
}