/*
    * Copyright (C) 2016, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.util.time;
  
  import static java.util.concurrent.TimeUnit.MICROSECONDS;
  import static java.util.concurrent.TimeUnit.MILLISECONDS;
  
  import java.time.Duration;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * A {@link org.eclipse.jgit.util.time.MonotonicClock} based on
   * {@code System.currentTimeMillis}.
   *
   * @since 4.6
   */
  public class MonotonicSystemClock implements MonotonicClock {
  	private static final AtomicLong before = new AtomicLong();
  
  	private static long nowMicros() {
  		long now = MILLISECONDS.toMicros(System.currentTimeMillis());
  		for (;;) {
  			long o = before.get();
  			long n = Math.max(o + 1, now);
  			if (before.compareAndSet(o, n)) {
  				return n;
  			}
  		}
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public ProposedTimestamp propose() {
  		final long u = nowMicros();
  		return new ProposedTimestamp() {
  			@Override
  			public long read(TimeUnit unit) {
  				return unit.convert(u, MICROSECONDS);
  			}
  
  			@Override
  			public void blockUntil(Duration maxWait) {
  				// Assume system clock never goes backwards.
  			}
  		};
  	}
  }