/*******************************************************************************
 * ============LICENSE_START==================================================
 * * org.onap.dmaap
 * * ===========================================================================
 * * Copyright © 2017 AT&T Intellectual Property. All rights reserved.
 * * ===========================================================================
 * * Licensed 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.
 * * ============LICENSE_END====================================================
 * *
 * * ECOMP is a trademark and service mark of AT&T Intellectual Property.
 * *
 ******************************************************************************/


package org.onap.dmaap.datarouter.node;

import java.util.*;

/**
 * Execute an operation no more frequently than a specified interval
 */

public abstract class RateLimitedOperation implements Runnable {
    private boolean marked;    // a timer task exists
    private boolean executing;    // the operation is currently in progress
    private boolean remark;    // a request was made while the operation was in progress
    private Timer timer;
    private long last;    // when the last operation started
    private long mininterval;

    /**
     * Create a rate limited operation
     *
     * @param mininterval The minimum number of milliseconds after the last execution starts before a new execution can begin
     * @param timer       The timer used to perform deferred executions
     */
    public RateLimitedOperation(long mininterval, Timer timer) {
        this.timer = timer;
        this.mininterval = mininterval;
    }

    private class deferred extends TimerTask {
        public void run() {
            execute();
        }
    }

    private synchronized void unmark() {
        marked = false;
    }

    private void execute() {
        unmark();
        request();
    }

    /**
     * Request that the operation be performed by this thread or at a later time by the timer
     */
    public void request() {
        if (premark()) {
            return;
        }
        do {
            run();
        } while (demark());
    }

    private synchronized boolean premark() {
        if (executing) {
            // currently executing - wait until it finishes
            remark = true;
            return (true);
        }
        if (marked) {
            // timer currently running - will run when it expires
            return (true);
        }
        long now = System.currentTimeMillis();
        if (last + mininterval > now) {
            // too soon - schedule a timer
            marked = true;
            timer.schedule(new deferred(), last + mininterval - now);
            return (true);
        }
        last = now;
        executing = true;
        // start execution
        return (false);
    }

    private synchronized boolean demark() {
        executing = false;
        if (remark) {
            remark = false;
            return (!premark());
        }
        return (false);
    }
}