/*******************************************************************************
 * Copyright (c) 2000, 2016 IBM Corporation and others.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 *******************************************************************************/
package org.eclipse.dltk.internal.core.search.processing;

import java.util.concurrent.atomic.AtomicInteger;

import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.OperationCanceledException;
import org.eclipse.core.runtime.SubMonitor;
import org.eclipse.dltk.core.DLTKCore;
import org.eclipse.dltk.internal.core.util.Messages;
import org.eclipse.dltk.internal.core.util.Util;
import org.eclipse.osgi.util.NLS;

public abstract class JobManager implements Runnable {

	/* enable delay between processing jobs if single core || multithreading */
	private static final boolean ENABLE_DELAYS = Runtime.getRuntime().availableProcessors() == 1;

	/* queue of jobs to execute */
	protected IJob[] awaitingJobs = new IJob[10];
	protected int jobStart = 0;
	protected int jobEnd = -1;
	protected boolean executing = false;

	/* background processing */
	protected Thread processingThread;

	/*
	 * counter indicating whether job execution is enabled or not, disabled if <= 0
	 * it cannot go beyond 1
	 */
	private int enableCount = 1;

	public final static boolean VERBOSE = DLTKCore.VERBOSE_JOBMANAGER;
	/* flag indicating that the activation has completed */
	public boolean activated = false;

	private final AtomicInteger awaitingClients = new AtomicInteger();

	/**
	 * Invoked exactly once, in background, before starting processing any job
	 */
	public void activateProcessing() {
		this.activated = true;
	}

	/**
	 * Answer the amount of awaiting jobs.
	 */
	public synchronized int awaitingJobsCount() {
		// pretend busy in case concurrent job attempts performing before
		// activated
		return this.activated ? this.jobEnd - this.jobStart + 1 : 1;
	}

	/**
	 * Answers the first job in the queue, or null if there is no job available
	 * Until the job has completed, the job manager will keep answering the same
	 * job.
	 */
	public synchronized IJob currentJob() {
		if (this.enableCount > 0 && this.jobStart <= this.jobEnd)
			return this.awaitingJobs[this.jobStart];
		return null;
	}

	public void disable() {
		this.enableCount--;
		if (VERBOSE)
			Util.verbose("DISABLING background indexing"); //$NON-NLS-1$
	}

	/**
	 * Remove the index from cache for a given project. Passing null as a job family
	 * discards them all.
	 */
	public void discardJobs(String jobFamily) {

		if (VERBOSE)
			Util.verbose("DISCARD   background job family - " + jobFamily); //$NON-NLS-1$

		try {
			IJob currentJob;
			// cancel current job if it belongs to the given family
			synchronized (this) {
				currentJob = this.currentJob();
				disable();
			}
			if (currentJob != null && (jobFamily == null || currentJob.belongsTo(jobFamily))) {
				currentJob.cancel();

				// wait until current active job has finished
				while (this.processingThread != null && this.executing) {
					try {
						if (VERBOSE)
							Util.verbose("-> waiting end of current background job - " + currentJob); //$NON-NLS-1$
						Thread.sleep(50);
					} catch (InterruptedException e) {
						// ignore
					}
				}
			}

			// flush and compact awaiting jobs
			int loc = -1;
			synchronized (this) {
				for (int i = this.jobStart; i <= this.jobEnd; i++) {
					currentJob = this.awaitingJobs[i];
					if (currentJob != null) { // sanity check
						this.awaitingJobs[i] = null;
						if (!(jobFamily == null || currentJob.belongsTo(jobFamily))) { // copy down,
							// compacting
							this.awaitingJobs[++loc] = currentJob;
						} else {
							if (VERBOSE)
								Util.verbose("-> discarding background job  - " + currentJob); //$NON-NLS-1$
							currentJob.cancel();
						}
					}
				}
				this.jobStart = 0;
				this.jobEnd = loc;
			}
		} finally {
			enable();
		}
		if (VERBOSE)
			Util.verbose("DISCARD   DONE with background job family - " + jobFamily); //$NON-NLS-1$
	}

	public synchronized void enable() {
		this.enableCount++;
		if (VERBOSE)
			Util.verbose("ENABLING  background indexing"); //$NON-NLS-1$
		this.notifyAll(); // wake up the background thread if it is waiting
		// (context must be synchronized)
	}

	public synchronized boolean isJobWaiting(IJob request) {
		for (int i = this.jobEnd; i > this.jobStart; i--)
			// don't check job at jobStart, as it may have already started
			if (request.equals(this.awaitingJobs[i]))
				return true;
		return false;
	}

	/**
	 * Advance to the next available job, once the current one has been completed.
	 * Note: clients awaiting until the job count is zero are still waiting at this
	 * point.
	 */
	protected synchronized void moveToNextJob() {
		// if (!enabled) return;

		if (this.jobStart <= this.jobEnd) {
			this.awaitingJobs[this.jobStart++] = null;
			if (this.jobStart > this.jobEnd) {
				this.jobStart = 0;
				this.jobEnd = -1;
			}
		}
	}

	/**
	 * Notifies that processing thread idle state has come to an end.
	 */
	protected void notifyIdle(long idlingTime) {
		// do nothing
	}

	/**
	 * Notifies that processing thread is going to idle state.
	 */
	protected void notifyIdle() {
		// do nothing
	}

	/**
	 * This API is allowing to run one job in concurrence with background
	 * processing. Indeed since other jobs are performed in background, resource
	 * sharing might be an issue.Therefore, this functionality allows a given job to
	 * be run without colliding with background ones. Note: multiple thread might
	 * attempt to perform concurrent jobs at the same time, and should synchronize
	 * (it is deliberately left to clients to decide whether concurrent jobs might
	 * interfere or not. In general, multiple read jobs are ok).
	 *
	 * Waiting policy can be: IJobConstants.ForceImmediateSearch
	 * IJobConstants.CancelIfNotReadyToSearch IJobConstants.WaitUntilReadyToSearch
	 *
	 */
	public boolean performConcurrentJob(IJob searchJob, int waitingPolicy, IProgressMonitor monitor) {
		if (VERBOSE)
			Util.verbose("STARTING  concurrent job - " + searchJob); //$NON-NLS-1$

		boolean status = IJob.FAILED;
		searchJob.ensureReadyToRun();
		try {
			SubMonitor subMonitor = SubMonitor.convert(monitor);
			if (awaitingJobsCount() > 0) {
				switch (waitingPolicy) {

				case IJob.ForceImmediate:
					if (VERBOSE)
						Util.verbose("-> NOT READY - forcing immediate - " + searchJob);//$NON-NLS-1$
					try {
						disable(); // pause indexing
						status = searchJob.execute(subMonitor);
					} finally {
						enable();
					}
					if (VERBOSE)
						Util.verbose("FINISHED  concurrent job - " + searchJob); //$NON-NLS-1$
					return status;

				case IJob.CancelIfNotReady:
					if (VERBOSE)
						Util.verbose("-> NOT READY - cancelling - " + searchJob); //$NON-NLS-1$
					if (VERBOSE)
						Util.verbose("CANCELED concurrent job - " + searchJob); //$NON-NLS-1$
					throw new OperationCanceledException();

				case IJob.WaitUntilReady:
					SubMonitor subProgress = subMonitor.setWorkRemaining(10).split(8).setWorkRemaining(1000);

					if (ENABLE_DELAYS) {
						synchronized (delaySignal) {
							delaySignal.notify();
						}
					}

					// use local variable to avoid potential NPE (see bug 20435 NPE
					// when searchingscriptmethod
					// and bug 42760 NullPointerException in JobManager when
					// searching)
					Thread t = this.processingThread;
					int originalPriority = t == null ? -1 : t.getPriority();
					try {
						if (t != null)
							t.setPriority(Thread.currentThread().getPriority());
						this.awaitingClients.incrementAndGet();
						IJob previousJob = null;
						int awaitingWork;
						while ((awaitingWork = awaitingJobsCount()) > 0) {
							if (subProgress != null && subProgress.isCanceled())
								throw new OperationCanceledException();
							final IJob currentJob = currentJob();
							// currentJob can be null when jobs have been added to
							// the queue but job manager is not enabled
							if (currentJob != null && currentJob != previousJob) {
								if (VERBOSE)
									Util.verbose("-> NOT READY - waiting until ready - " + searchJob);//$NON-NLS-1$
								subProgress.subTask(
										NLS.bind(Messages.manager_filesToIndex, Integer.toString(awaitingWork)));
								subProgress.worked(1);
								previousJob = currentJob;
							}
							try {
								if (VERBOSE)
									Util.verbose("-> GOING TO SLEEP - " + searchJob);//$NON-NLS-1$
								Thread.sleep(50);
							} catch (InterruptedException e) {
								// ignore
							}
						}
					} finally {
						this.awaitingClients.decrementAndGet();
						if (t != null && originalPriority > -1 && t.isAlive())
							t.setPriority(originalPriority);
					}
				}
			}
			status = searchJob.execute(subMonitor);
			if (VERBOSE)
				Util.verbose("FINISHED  concurrent job - " + searchJob); //$NON-NLS-1$
		} finally {
			SubMonitor.done(monitor);
		}
		return status;
	}

	public abstract String processName();

	private static final class WaitJob implements IJob {
		@Override
		public boolean belongsTo(String jobFamily) {
			return false;
		}

		@Override
		public void cancel() {
		}

		@Override
		public void ensureReadyToRun() {
		}

		@Override
		public boolean execute(IProgressMonitor progress) {
			return false;
		}

		@Override
		public String toString() {
			return "WAIT-UNTIL-READY-JOB"; //$NON-NLS-1$
		}
	}

	public void waitUntilReady() {
		performConcurrentJob(new WaitJob(), IJob.WaitUntilReady, null);
	}

	/**
	 * @since 2.0
	 */
	public void requestIfNotWaiting(IJob job) {
		if (!isJobWaiting(job)) {
			request(job);
		}
	}

	public synchronized void request(IJob job) {

		job.ensureReadyToRun();

		// append the job to the list of ones to process later on
		int size = this.awaitingJobs.length;
		if (++this.jobEnd == size) { // when growing, relocate jobs starting at
			// position 0
			this.jobEnd -= this.jobStart;
			System.arraycopy(this.awaitingJobs, this.jobStart, this.awaitingJobs = new IJob[size * 2], 0, this.jobEnd);
			this.jobStart = 0;
		}
		this.awaitingJobs[this.jobEnd] = job;
		if (VERBOSE) {
			Util.verbose("REQUEST   background job - " + job); //$NON-NLS-1$
			Util.verbose("AWAITING JOBS count: " + awaitingJobsCount()); //$NON-NLS-1$
		}
		notifyAll(); // wake up the background thread if it is waiting
	}

	/**
	 * Flush current state
	 */
	public synchronized void reset() {
		if (VERBOSE)
			Util.verbose("Reset"); //$NON-NLS-1$

		if (this.processingThread != null) {
			discardJobs(null); // discard all jobs
		} else {
			/* initiate background processing */
			this.processingThread = new Thread(this, this.processName());
			this.processingThread.setDaemon(true);
			// less prioritary by default, priority is raised if clients are
			// actively waiting on it
			this.processingThread.setPriority(Thread.NORM_PRIORITY - 1);
			this.processingThread.start();
		}
	}

	/**
	 * is used for delaying before processing new jobs, that could be canceled by
	 * {@link #performConcurrentJob()} if called with {@link IJob#WaitUntilReady}
	 */
	private final Object delaySignal = new Object();

	/**
	 * Infinite loop performing resource indexing
	 */
	@Override
	public void run() {
		long idlingStart = -1;
		activateProcessing();
		try {
			while (this.processingThread != null) {
				try {
					IJob job;
					synchronized (this) {
						// handle shutdown case when notifyAll came before the
						// wait but after the while loop was entered
						if (this.processingThread == null)
							continue;

						// must check for new job inside this sync block to
						// avoid timing hole
						if ((job = currentJob()) == null) {
							if (idlingStart < 0) {
								idlingStart = System.currentTimeMillis();
								notifyIdle();
							} else
								notifyIdle(System.currentTimeMillis() - idlingStart);
							this.wait(); // wait until a new job is posted (or
							// reenabled:38901)
						} else {
							idlingStart = -1;
						}
					}
					if (job == null) {
						notifyIdle(System.currentTimeMillis() - idlingStart);
						// just woke up, delay before processing any new jobs,
						// allow some time for the active thread to finish
						if (ENABLE_DELAYS) {
							synchronized (delaySignal) {
								delaySignal.wait(50);
							}
						}
						continue;
					}
					if (VERBOSE) {
						Util.verbose(awaitingJobsCount() + " awaiting jobs"); //$NON-NLS-1$
						Util.verbose("STARTING background job - " + job); //$NON-NLS-1$
					}
					try {
						this.executing = true;
						/* boolean status = */job.execute(null);
						// if (status == FAILED) request(job);
					} finally {
						this.executing = false;
						if (VERBOSE)
							Util.verbose("FINISHED background job - " + job); //$NON-NLS-1$
						moveToNextJob();
						if (ENABLE_DELAYS && this.awaitingClients.get() == 0)
							Thread.sleep(50);
					}
				} catch (InterruptedException e) { // background indexing was
					// interrupted
				}
			}
		} catch (RuntimeException e) {
			if (this.processingThread != null) { // if not shutting down
				// keep job manager alive
				this.discardJobs(null);
				this.processingThread = null;
				this.reset(); // this will fork a new thread with no waiting
				// jobs, some indexes will be inconsistent

				// log exception
				Util.log(e, "Background Indexer Crash Recovery"); //$NON-NLS-1$
			}
			throw e;
		} catch (Error e) {
			if (this.processingThread != null && !(e instanceof ThreadDeath)) {
				// keep job manager alive
				this.discardJobs(null);
				this.processingThread = null;
				this.reset(); // this will fork a new thread with no waiting
				// jobs, some indexes will be inconsistent

				// log exception
				Util.log(e, "Background Indexer Crash Recovery"); //$NON-NLS-1$
			}
			throw e;
		}
	}

	/**
	 * Stop background processing, and wait until the current job is completed
	 * before returning
	 */
	public void shutdown() {

		if (VERBOSE)
			Util.verbose("Shutdown"); //$NON-NLS-1$

		disable();
		discardJobs(null); // will wait until current executing job has
		// completed
		Thread thread = this.processingThread;
		try {
			if (thread != null) { // see
				// http://bugs.eclipse.org/bugs/show_bug.cgi
				// ?id=31858
				synchronized (this) {
					this.processingThread = null; // mark the job manager as
					// shutting down so that the
					// thread will stop by
					// itself
					this.notifyAll(); // ensure its awake so it can be shutdown
				}
				// in case processing thread is handling a job
				// XXX wait not more than 1 minute
				thread.join(60000);
			}
		} catch (InterruptedException e) {
			// ignore
		}
	}

	@Override
	public String toString() {
		StringBuilder buffer = new StringBuilder(64);
		buffer.append("Enable count:").append(this.enableCount).append('\n'); //$NON-NLS-1$
		int numJobs = this.jobEnd - this.jobStart + 1;
		buffer.append("Jobs in queue:").append(numJobs).append('\n'); //$NON-NLS-1$
		for (int i = 0; i < numJobs && i < 15; i++) {
			buffer.append(i).append(" - job[" + i + "]: ").append(this.awaitingJobs[this.jobStart + i]).append('\n'); //$NON-NLS-1$ //$NON-NLS-2$
		}
		return buffer.toString();
	}
}