/*******************************************************************************
 * Copyright (c) 2007, 2011 Association for Decentralized Information Management
 * in Industry THTH ry.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     VTT Technical Research Centre of Finland - initial API and implementation
 *******************************************************************************/
package org.simantics.ui.jobs;

import java.util.function.Consumer;

import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.core.runtime.jobs.Job;
import org.simantics.DatabaseJob;
import org.simantics.Simantics;
import org.simantics.db.Session;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.layer0.util.SessionGarbageCollection;
import org.simantics.db.service.LifecycleSupport;
import org.simantics.utils.ui.ErrorLogger;

/**
 * @author Tuukka Lehtonen
 */
public class SessionGarbageCollectorJob extends Job {

    private static SessionGarbageCollectorJob instance;

    public synchronized static SessionGarbageCollectorJob getInstance() {
        if (instance == null)
            instance = new SessionGarbageCollectorJob();
        return instance;
    }

    private static final boolean TRACE                  = false;

    /**
     * At least 60 seconds between executions.
     */
    private static final long    DEFAULT_QUIET_TIME     = 5000;

    private long                 start;
    private long                 quietTime;
    private long                 userDefinedQuietTime;

    private boolean              enabled                = true;

    /**
     * 
     */
    public SessionGarbageCollectorJob() {
        this(DEFAULT_QUIET_TIME);
    }

    /**
     * @param delayBetweenExecutions
     */
    public SessionGarbageCollectorJob(long delayBetweenExecutions) {
        super("Database Garbage Collector");
        setPriority(Job.DECORATE);

        // Hide job from users.
        setSystem(true);

        this.start = System.currentTimeMillis();
        this.quietTime = delayBetweenExecutions;
        this.userDefinedQuietTime = delayBetweenExecutions;
    }

    /**
     * Cancels the currently scheduled execution of this job and reschedules
     * another execution after the current quiet time. This can be used for
     * easily pushing GC back a bit while performing an operation during which
     * it is not efficient to GC.
     *
     * @see #setQuietTime(long)
     */
    public void rescheduleAfterQuietTime() {
        cancel();
        scheduleAfterQuietTime();
    }

    /**
     * Cancels the currently scheduled execution of this job and reschedules
     * another with no delay. This can be used for immediate forced execution of
     * session GC.
     */
    public void rescheduleNow() {
        cancel();
        schedule();
    }

    /**
     * @param enabled
     * @return
     */
    public SessionGarbageCollectorJob setEnabled(boolean enabled) {
        this.enabled = enabled;
        return this;
    }

//    /**
//     * @param quietTime quiet time between collections in
//     *        milliseconds
//     */
//    public SessionGarbageCollectorJob setQuietTime(long quietTime) {
//        this.quietTime = quietTime;
//        return this;
//    }

    /**
     * Schedules this job after the currently set quiet time.
     * 
     * @see #setQuietTime(long)
     */
    public void scheduleAfterQuietTime() {
        schedule(quietTime);
    }

    @Override
    public boolean shouldSchedule() {
        return enabled;
    }

    @Override
    public boolean shouldRun() {
        if (TRACE) {
            if (!enabled) {
                long t = System.currentTimeMillis();
                System.out.println("GC disabled, not running @ " + ((double) (t - start) * 1e-3) + " seconds");
            }
        }
        return enabled;
    }

    /**
     * Only invoked with actual errors, not <code>null</code> values.
     */
    Consumer<DatabaseException> errorCallback = e -> ErrorLogger.defaultLogError(e);

    @Override
    protected IStatus run(IProgressMonitor monitor) {
        long interval = quietTime;
        try {
            Session session = Simantics.peekSession();
            if (session == null)
                return Status.CANCEL_STATUS;
            LifecycleSupport lfs = session.peekService(LifecycleSupport.class);
            if (lfs == null || lfs.isClosed() || lfs.isClosing())
                return Status.CANCEL_STATUS;

            // Never run while a heavy database job is in progress.
            if (DatabaseJob.inProgress()) {
                // Schedule again in at most 10 seconds instead of
                // waiting for the whole quiet time period again.
                interval = Math.min(10, quietTime);
                return Status.CANCEL_STATUS;
            }

//            // Don't run if there are currently write requests in progress
//            TransactionSupport ts = session.getService(TransactionSupport.class);
//            if (ts.getWriteCount() > 0) {
//                if (TRACE) {
//                    long t = System.currentTimeMillis();
//                    System.out.println("Write in progress, no GC @ " + ((double) (t - start) * 1e-3) + " seconds");
//                }
//                return Status.CANCEL_STATUS;
//            }

            long begin = System.currentTimeMillis();
            if (TRACE) {
                System.out.println("running GC @ " + ((double) (begin - start) * 1e-3) + " seconds");
            }

            boolean busy = SessionGarbageCollection.gc(monitor, session, true, errorCallback);
            if(busy) {
            	quietTime = Math.max((3*quietTime)/4, 100);
            } else {
            	if(quietTime < userDefinedQuietTime)
            		quietTime = Math.min(userDefinedQuietTime, (long)(1.2*quietTime));
            }

            if (TRACE)
            	if(busy)
            		System.err.println("Session GC ended busy. New quiet time is " + quietTime);
            
            // This quiet time might have been adjusted in GC
            interval = quietTime;

            long intermediate = System.currentTimeMillis();

            // Clean up heap of all garbage left behind by SessionGarbageCollection 
            //System.gc();

            if (TRACE) {
                //long end = System.currentTimeMillis();
                //System.out.println("Session.GC " + (intermediate - begin) + "ms, System.GC " + (end-intermediate) + "ms, total " + (end - begin) + "ms");
                System.out.println("Session.GC " + (intermediate - begin) + "ms");
            }

            // Reschedule after a quiet period.
            return Status.OK_STATUS;
        } finally {
            schedule(interval);
            monitor.done();
        }
    }

}