/*
 * 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.beam.sdk.state;

import javax.annotation.Nullable;
import org.apache.beam.sdk.annotations.Experimental;
import org.joda.time.Instant;

/** Interface for interacting with time. */
@Experimental(Experimental.Kind.TIMERS)
public interface Timers {
  /**
   * Sets a timer to fire when the event time watermark, the current processing time, or the
   * synchronized processing time watermark surpasses a given timestamp.
   *
   * <p>See {@link TimeDomain} for details on the time domains available.
   *
   * <p>Timers are not guaranteed to fire immediately, but will be delivered at some time
   * afterwards.
   *
   * <p>An implementation of {@link Timers} implicitly scopes timers that are set - they may be
   * scoped to a key and window, or a key, window, and trigger, etc.
   *
   * @param timestamp the time at which the timer should be delivered
   * @param timeDomain the domain that the {@code timestamp} applies to
   */
  void setTimer(Instant timestamp, TimeDomain timeDomain);

  /** Removes the timer set in this context for the {@code timestmap} and {@code timeDomain}. */
  void deleteTimer(Instant timestamp, TimeDomain timeDomain);

  /** Returns the current processing time. */
  Instant currentProcessingTime();

  /** Returns the current synchronized processing time or {@code null} if unknown. */
  @Nullable
  Instant currentSynchronizedProcessingTime();

  /** Returns the current event time. */
  Instant currentEventTime();
}
