/**
 * A simple Stopwatch utility for measuring time in milliseconds.
 *
 * @author  Stefan Nilsson
 * @version 2009-02-10
 */
public class Stopwatch {
    /**
     * Time when start() was called. Contains a valid time
     * only if the clock is running.
     */
    private long startTime;

    /**
     * Holds the total accumulated time since last reset.
     * Does not include time since start() if clock is running.
     */
    private long totalTime = 0;

    private boolean isRunning = false;

    /**
     * Constructs a new Stopwatch. The new clock is not
     * running and the total time is set to 0.
     */
    public Stopwatch() {
    }

    /**
     * Turns this clock on.
     * Has no effect if the clock is already running.
     *
     * @return a reference to this Stopwatch.
     */
    public Stopwatch start() {
        if (!isRunning) {
            isRunning = true;
            startTime = System.nanoTime();
        }
	return this;
    }

    /**
     * Turns this clock off.
     * Has no effect if the clock is not running.
     *
     * @return a reference to this Stopwatch.
     */
    public Stopwatch stop() {
        if (isRunning) {
            totalTime += System.nanoTime() - startTime;
            isRunning = false;
        }
	return this;
    }

    /**
     * Resets this clock.
     * The clock is stopped and the total time is set to 0.
     *
     * @return a reference to this Stopwatch.
     */
    public Stopwatch reset() {
        isRunning = false;
        totalTime = 0;
	return this;
    }

    /**
     * Returns the total time that this clock has been running since
     * last reset.
     * Does not affect the running status of the clock; if the clock
     * is running when this method is called, it continues to run.
     *
     * @return the time in milliseconds.
     */
    public long getTime() {
        return getTimeNano() / 1000000;
    }

    private long getTimeNano() {
        return totalTime +
            (isRunning ? System.nanoTime() - startTime : 0);
    }

    /**
     * Tests if this clock is running.
     *
     * @return <tt>true</tt> if this clock is running;
     *         <tt>false</tt> otherwise.
     */
    public boolean isRunning() {
        return isRunning;
    }

    /**
     * Returns a string description of this clock. The exact details
     * of the representation are unspecified and subject to change,
     * but this is typical: "25 ms (running)".
     */
    @Override public String toString() {
	return getTime() + " ms" +
	    (isRunning() ? " (running)" : " (stopped)");
    }
}