/*******************************************************************************
 *
 * Copyright (c) 2004-2010 Oracle Corporation.
 *
 * 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:
 *
 *
 *******************************************************************************/ 

package hudson.model;

import hudson.Extension;
import hudson.ExtensionList;
import hudson.ExtensionPoint;

import java.io.IOException;

/**
 * Extension point that allows plugins to veto the restart.
 *
 * @author Kohsuke Kawaguchi
 * @since 1.376
 */
public abstract class RestartListener implements ExtensionPoint {

    /**
     * Called periodically during the safe restart.
     *
     * @return false to block the restart
     */
    public abstract boolean isReadyToRestart() throws IOException, InterruptedException;

    /**
     * Called immediately before the restart is actually triggered.
     */
    public void onRestart() {
    }

    /**
     * Returns all the registered {@link LabelFinder}s.
     */
    public static ExtensionList<RestartListener> all() {
        return Hudson.getInstance().getExtensionList(RestartListener.class);
    }

    /**
     * Returns true iff all the listeners OKed the restart.
     */
    public static boolean isAllReady() throws IOException, InterruptedException {
        for (RestartListener listener : all()) {
            if (!listener.isReadyToRestart()) {
                return false;
            }
        }
        return true;
    }

    /**
     * Default logic. Wait for all the executors to become idle.
     */
    @Extension
    public static class Default extends RestartListener {

        @Override
        public boolean isReadyToRestart() throws IOException, InterruptedException {
            Hudson h = Hudson.getInstance();
            return h.overallLoad.computeTotalExecutors() <= h.overallLoad.computeIdleExecutors();
        }
    }
}