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package org.javasimon.clock;

/**
 * Interface for getting current time. By default {@link Clock#SYSTEM} is used to match System timers,
 * but different implementation can be used to provide different time for {@link org.javasimon.Manager}.
 * This also allows easier testing without sleeping.
 *
 * @author Ivan Mushketyk
 * @since 3.5
 */
public interface Clock {

	/**
	 * Gets current time in nanoseconds.
	 *
	 * @return current time in nanoseconds
	 */
	long nanoTime();

	/**
	 * Gets current time in milliseconds.
	 *
	 * @return current time in milliseconds
	 */
	long milliTime();

	/**
	 * Converts nano timer value into millis timestamp compatible with {@link #milliTime()} without actually
	 * using the timer. Method does not just divide nanos by one million, but also works with remembered
	 * values for milli- and nano-timers at one particular moment.
	 *
	 * @param nanos nano timer value
	 * @return ms timestamp
	 * @since 3.5 (before in SimonUtils since 3.3, before in SimonManager since 3.1)
	 */
	long millisForNano(long nanos);

	/** Default implementation using {@link java.lang.System#currentTimeMillis()} and {@link java.lang.System#nanoTime()}. */
	Clock SYSTEM = new Clock() {
		@Override
		public long nanoTime() {
			return System.nanoTime();
		}

		@Override
		public long milliTime() {
			return System.currentTimeMillis();
		}

		@Override
		public long millisForNano(long nanos) {
			return ClockUtils.millisForNano(nanos);
		}
	};

	/** Clock implementation measuring CPU time. */
	Clock CPU = new CpuClock();
}