// Copyright (C) 2002 Jon A. Maxwell (JAM)
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

package net.sourceforge.jnlp.cache;

/**
 * A policy that determines when a resource should be checked for
 * an updated version.<p>
 *
 * @author <a href="mailto:jmaxwell@users.sourceforge.net">Jon A. Maxwell (JAM)</a> - initial author
 * @version $Revision: 1.3 $
 */
public class UpdatePolicy {

    // todo: implement session updating

    // todo: doesn't seem to work in the same JVM, probably because
    // Resource is being held by a tracker so it isn't collected;
    // then next time a tracker adds the resource even if
    // shouldUpdate==true it's state is already marked
    // CONNECTED|DOWNLOADED.  Let the resource be collected or reset
    // to UNINITIALIZED.

    public static UpdatePolicy ALWAYS = new UpdatePolicy(0);
    public static UpdatePolicy SESSION = new UpdatePolicy(-1);
    public static UpdatePolicy FORCE = new UpdatePolicy(Long.MIN_VALUE);
    public static UpdatePolicy NEVER = new UpdatePolicy(Long.MAX_VALUE);

    private long timeDiff = -1;

    /**
     * Create a new update policy; this policy always updates the
     * entry unless the shouldUpdate method is overridden.
     */
    public UpdatePolicy() {
    }

    /**
     * Create an update policy that only checks a file for being
     * updated if it has not been checked for longer than the
     * specified time.
     *
     * @param timeDiff how long in ms until update needed
     */
    public UpdatePolicy(long timeDiff) {
        this.timeDiff = timeDiff;
    }

    /**
     * Returns whether the resource should be checked for being
     * up-to-date.
     */
    public boolean shouldUpdate(CacheEntry entry) {
        long updated = entry.getLastUpdated();
        long current = System.currentTimeMillis();

        if (current - updated >= timeDiff)
            return true;
        else
            return false;
    }

}