/*******************************************************************************
 *
 * Copyright (c) 2010, InfraDNA, Inc.
 *
 * 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.queue;

import hudson.Extension;
import hudson.ExtensionList;
import hudson.ExtensionPoint;
import hudson.model.Computer;
import hudson.model.Executor;
import hudson.model.Hudson;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Predicts future load to the system, to assist the scheduling decisions
 *
 * <p> When Hudson makes a scheduling decision, Hudson considers predicted
 * future load — e.g., "We do currently have one available executor, but
 * we know we need this for something else in 30 minutes, so we can't currently
 * schedule a build that takes 1 hour."
 *
 * <p> This extension point plugs in such estimation of future load.
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class LoadPredictor implements ExtensionPoint {

    /**
     * Estimates load starting from the 'start' timestamp, up to the 'end'
     * timestamp.
     *
     * @param start Where to start enumeration. Always bigger or equal to the
     * current time of the execution.
     * @param plan This is the execution plan for which we are making a load
     * prediction. Never null. While this object is still being partially
     * constructed when this method is called, some of its properties (like
     * {@link MappingWorksheet#item} provide access to more contextual
     * information.
     * @since 1.380
     */
    public Iterable<FutureLoad> predict(MappingWorksheet plan, Computer computer, long start, long end) {
        // maintain backward compatibility by calling the old signature.
        return predict(computer, start, end);
    }

    /**
     * Estimates load starting from the 'start' timestamp, up to the 'end'
     * timestamp.
     *
     * @param start Where to start enumeration. Always bigger or equal to the
     * current time of the execution.
     * @deprecated as of 1.380 Use
     * {@link #predict(MappingWorksheet, Computer, long, long)}
     */
    public Iterable<FutureLoad> predict(Computer computer, long start, long end) {
        return Collections.emptyList();
    }

    /**
     * All the registered instances.
     */
    public static ExtensionList<LoadPredictor> all() {
        return Hudson.getInstance().getExtensionList(LoadPredictor.class);
    }

    /**
     * Considers currently running tasks and their completion.
     */
    @Extension
    public static class CurrentlyRunningTasks extends LoadPredictor {

        @Override
        public Iterable<FutureLoad> predict(MappingWorksheet plan, final Computer computer, long start, long eternity) {
            long now = System.currentTimeMillis();
            List<FutureLoad> fl = new ArrayList<FutureLoad>();
            for (Executor e : computer.getExecutors()) {
                if (e.isIdle()) {
                    continue;
                }

                long eta = e.getEstimatedRemainingTimeMillis();
                long end = eta < 0 ? eternity : now + eta; // when does this task end?
                if (end < start) {
                    continue;   // should be over by the 'start' time.
                }
                fl.add(new FutureLoad(start, end - start, 1));
            }
            return fl;
        }
    }
}