/*
 * The MIT License
 * 
 * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package hudson.model;

import org.kohsuke.stapler.StaplerRequest;
import org.kohsuke.stapler.StaplerResponse;

import javax.servlet.ServletException;
import java.io.IOException;
import java.util.LinkedHashSet;
import java.util.SortedMap;

import hudson.model.Descriptor.FormException;

/**
 * {@link Job} that monitors activities that happen outside Hudson,
 * which requires occasional batch reload activity to obtain the up-to-date information.
 *
 * <p>
 * This can be used as a base class to derive custom {@link Job} type.
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class ViewJob<JobT extends ViewJob<JobT,RunT>, RunT extends Run<JobT,RunT>>
    extends Job<JobT,RunT> {

    /**
     * We occasionally update the list of {@link Run}s from a file system.
     * The next scheduled update time.
     */
    private transient long nextUpdate = 0;

    /**
     * All {@link Run}s. Copy-on-write semantics.
     */
    protected transient /*almost final*/ RunMap<RunT> runs = new RunMap<RunT>();

    private transient boolean notLoaded = true;

    /**
     * If the reloading of runs are in progress (in another thread,
     * set to true.)
     */
    private transient volatile boolean reloadingInProgress;

    /**
     * {@link ExternalJob}s that need to be reloaded.
     *
     * This is a set, so no {@link ExternalJob}s are scheduled twice, yet
     * it's order is predictable, avoiding starvation.
     */
    private static final LinkedHashSet<ViewJob> reloadQueue = new LinkedHashSet<ViewJob>();
    /*package*/ static final Thread reloadThread = new ReloadThread();
    static {
        reloadThread.start();
    }

    /**
     * @deprecated as of 1.390
     */
    protected ViewJob(Hudson parent, String name) {
        super(parent,name);
    }

    protected ViewJob(ItemGroup parent, String name) {
        super(parent,name);
    }

    public boolean isBuildable() {
        return false;
    }

    @Override
    public void onLoad(ItemGroup<? extends Item> parent, String name) throws IOException {
        super.onLoad(parent, name);
        notLoaded = true;
    }

    protected SortedMap<Integer,RunT> _getRuns() {
        if(notLoaded || runs==null) {
            // if none is loaded yet, do so immediately.
            synchronized(this) {
                if(runs==null)
                    runs = new RunMap<RunT>();
                if(notLoaded) {
                    notLoaded = false;
                    _reload();   
                }
            }
        }
        if(nextUpdate<System.currentTimeMillis()) {
            if(!reloadingInProgress) {
                // schedule a new reloading operation.
                // we don't want to block the current thread,
                // so reloading is done asynchronously.
                reloadingInProgress = true;
                synchronized(reloadQueue) {
                    reloadQueue.add(this);
                    reloadQueue.notify();
                }
            }
        }
        return runs;
    }

    public void removeRun(RunT run) {
        // reload the info next time
        nextUpdate = 0;
    }

    private void _reload() {
        try {
            reload();
        } finally {
            reloadingInProgress = false;
            nextUpdate = reloadPeriodically ? System.currentTimeMillis()+1000*60 : Long.MAX_VALUE;
        }
    }

    /**
     * Reloads the list of {@link Run}s. This operation can take a long time.
     *
     * <p>
     * The loaded {@link Run}s should be set to {@link #runs}.
     */
    protected abstract void reload();

    @Override
    protected void submit( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException, FormException {
        super.submit(req,rsp);
        // make sure to reload to reflect this config change.
        nextUpdate = 0;
    }


    /**
     * Thread that reloads the {@link Run}s.
     */
    private static final class ReloadThread extends Thread {
        private ReloadThread() {
            setName("ViewJob reload thread");
        }

        private ViewJob getNext() throws InterruptedException {
            synchronized(reloadQueue) {
                // reload operations might eat InterruptException,
                // so check the status every so often
                while(reloadQueue.isEmpty() && !terminating())
                    reloadQueue.wait(60*1000);
                if(terminating())
                    throw new InterruptedException();   // terminate now
                ViewJob job = reloadQueue.iterator().next();
                reloadQueue.remove(job);
                return job;
            }
        }

        private boolean terminating() {
            return Hudson.getInstance().isTerminating();
        }

        @Override
        public void run() {
            while (!terminating()) {
                try {
                    getNext()._reload();
                } catch (InterruptedException e) {
                    // treat this as a death signal
                    return;
                } catch (Throwable t) {
                    // otherwise ignore any error
                    t.printStackTrace();
                }
            }
        }
    }

    // private static final Logger logger = Logger.getLogger(ViewJob.class.getName());

    /**
     * In the very old version of Hudson, an external job submission was just creating files on the file system,
     * so we needed to periodically reload the jobs from a file system to pick up new records.
     *
     * <p>
     * We then switched to submission via HTTP, so this reloading is no longer necessary, so only do this
     * when explicitly requested.
     * 
     */
    public static boolean reloadPeriodically = Boolean.getBoolean(ViewJob.class.getName()+".reloadPeriodically");
}