/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.sysds.utils.stats;

/**
 * Helper class to time the execution of elements
 */
public class Timing {
	/** The current timers starting time */
	private long _start = -1;

	/**
	 * Get a timer that is started.
	 */
	public Timing() {
		this(true);
	}

	/**
	 * Get a timing that is optionally started
	 * 
	 * @param start If the timer should reset its time.
	 */
	public Timing(boolean start) {
		// init and start the timer
		if(start)
			start();
	}

	/**
	 * Starts the time measurement.
	 */
	public void start() {
		_start = System.nanoTime();
	}

	/**
	 * Measures and returns the time since the last start() or stop() invocation and restarts the measurement.
	 * 
	 * @return duration between start and stop
	 */
	public double stop() {
		if(_start == -1)
			throw new RuntimeException("Stop time measurement without prior start is invalid.");

		long end = System.nanoTime();
		double duration = ((double) (end - _start)) / 1000000;

		// carry end time over
		_start = end;
		return duration;
	}

	/**
	 * Measures and returns the time since the last start() or stop() invocation, restarts the measurement, and prints
	 * the last measurement to STDOUT.
	 */
	public void stopAndPrint() {
		double tmp = stop();
		System.out.println("PARFOR: time = " + tmp + "ms");
	}

	@Override
	public String toString(){
		return "Timing: " + stop();
	}
}
