/**
 * 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;

import java.time.Instant;

/**
 * An abstraction of the system clock.
 * @author John Sirois
 */
public interface Clock {
  // TODO(zmanji): Consider replacing this with java.time.Clock
  /**
   * A clock that returns the the actual time reported by the system.
   */
  Clock SYSTEM_CLOCK = new Clock() {
    @Override public long nowMillis() {
      return System.currentTimeMillis();
    }
    @Override public long nowNanos() {
      return System.nanoTime();
    }
    @Override public void waitFor(long millis) throws InterruptedException {
      Thread.sleep(millis);
    }
    @Override public Instant nowInstant() {
      return Instant.now();
    }
  };

  /**
   * Returns the current time in milliseconds since the epoch.
   *
   * @return The current time in milliseconds since the epoch.
   * @see System#currentTimeMillis()
   */
  long nowMillis();

  /**
   * Returns the current time in nanoseconds. Should be used only for relative timing.
   * See {@code System.nanoTime()} for tips on using the value returned here.
   *
   * @return A measure of the current time in nanoseconds.
   * @see System#nanoTime()
   */
  long nowNanos();

  /**
   * Waits for the given amount of time to pass on this clock before returning.
   *
   * @param millis the amount of time to wait in milliseconds
   * @throws InterruptedException if this wait was interrupted
   */
  void waitFor(long millis) throws InterruptedException;

  /**
   * Returns the current time as an java.time.Instant.
   *
   * @return the Instant representing the current time.
   * @see Instant#now()
   */
  Instant nowInstant();
}