package compbio.stat.servlet.util;

import java.util.TimerTask;


/**
 * A task that can be scheduled for recurring execution by a {@link Scheduler}.
 */
public abstract class SchedulerTask implements Runnable {

    final Object lock = new Object();

    int state = VIRGIN;
    static final int VIRGIN = 0;
    static final int SCHEDULED = 1;
    static final int CANCELLED = 2;

    TimerTask timerTask;

    /**
     * Creates a new scheduler task.
     */

    protected SchedulerTask() {
    }

    /**
     * The action to be performed by this scheduler task.
     */

    public abstract void run();

    /**
     * Cancels this scheduler task.
     * <p>
     * This method may be called repeatedly; the second and subsequent calls have no effect.
     *
     * @return true if this task was already scheduled to run
     */

    public boolean cancel() {
        synchronized (lock) {
            if (timerTask != null) {
                timerTask.cancel();
            }
            boolean result = (state == SCHEDULED);
            state = CANCELLED;
            return result;
        }
    }

    /**
     * Returns the <i>scheduled</i> execution time of the most recent actual execution of
     * this task. (If this method is invoked while task execution is in progress,
     * the return value is the scheduled execution time of the ongoing task execution.)
     *
     * @return the time at which the most recent execution of this task was scheduled
     * to occur, in the format returned by <code>Date.getTime()</code>. The return value
     * is undefined if the task has yet to commence its first execution.
     */

    public long scheduledExecutionTime() {
        synchronized (lock) {
            return timerTask == null ? 0 : timerTask.scheduledExecutionTime();
        }
    }

}