content: /**
   * Licensed 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.aurora.common.util.testing;
  
  import java.time.Instant;
  import java.util.concurrent.TimeUnit;
  
  import com.google.common.base.Preconditions;
  
  import org.apache.aurora.common.quantity.Amount;
  import org.apache.aurora.common.quantity.Time;
  import org.apache.aurora.common.util.Clock;
  
  /**
   * A clock for use in testing with a configurable value for {@link #nowMillis()}.
   *
   * @author John Sirois
   */
  public class FakeClock implements Clock {
    // Tests may need to use the clock from multiple threads, ensure liveness.
    private volatile long nowNanos;
  
    /**
     * Sets what {@link #nowMillis()} will return until this method is called again with a new value
     * for {@code now}.
     *
     * @param nowMillis the current time in milliseconds
     */
    public void setNowMillis(long nowMillis) {
      Preconditions.checkArgument(nowMillis >= 0);
      this.nowNanos = TimeUnit.MILLISECONDS.toNanos(nowMillis);
    }
  
    /**
     * Advances the current time by {@code millis} milliseconds.  Time can be retarded by passing a
     * negative value.
     *
     * @param period the amount of time to advance the current time by
     */
    public void advance(Amount<Long, Time> period) {
      Preconditions.checkNotNull(period);
      long newNanos = nowNanos + period.as(Time.NANOSECONDS);
      Preconditions.checkArgument(newNanos >= 0,
          "invalid period %s - would move current time to a negative value: %sns", period, newNanos);
      nowNanos = newNanos;
    }
  
    @Override
    public long nowMillis() {
      return TimeUnit.NANOSECONDS.toMillis(nowNanos);
    }
  
    @Override
    public long nowNanos() {
      return nowNanos;
    }
  
    /**
     * Waits in fake time, immediately returning in real time; however a check of {@link #nowMillis}
     * after this method completes will consistently reveal that {@code millis} did in fact pass while
     * waiting.
     *
     * @param millis the amount of time to wait in milliseconds
     */
    @Override
    public void waitFor(long millis) {
      advance(Amount.of(millis, Time.MILLISECONDS));
    }
  
    @Override
    public Instant nowInstant() {
      return Instant.ofEpochMilli(nowMillis());
    }
  }
  