/*
 * 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.flink.streaming.api.windowing.triggers;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.streaming.api.windowing.windows.Window;

/**
 * A trigger that can turn any {@link Trigger} into a purging {@code Trigger}.
 *
 * <p>When the nested trigger fires, this will return a {@code FIRE_AND_PURGE}
 * {@link TriggerResult}.
 *
 * @param <T> The type of elements on which this trigger can operate.
 * @param <W> The type of {@link Window Windows} on which this trigger can operate.
 */
@PublicEvolving
public class PurgingTrigger<T, W extends Window> extends Trigger<T, W> {
	private static final long serialVersionUID = 1L;

	private Trigger<T, W> nestedTrigger;

	private  PurgingTrigger(Trigger<T, W> nestedTrigger) {
		this.nestedTrigger = nestedTrigger;
	}

	@Override
	public TriggerResult onElement(T element, long timestamp, W window, TriggerContext ctx) throws Exception {
		TriggerResult triggerResult = nestedTrigger.onElement(element, timestamp, window, ctx);
		return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;
	}

	@Override
	public TriggerResult onEventTime(long time, W window, TriggerContext ctx) throws Exception {
		TriggerResult triggerResult = nestedTrigger.onEventTime(time, window, ctx);
		return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;
	}

	@Override
	public TriggerResult onProcessingTime(long time, W window, TriggerContext ctx) throws Exception {
		TriggerResult triggerResult = nestedTrigger.onProcessingTime(time, window, ctx);
		return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;
	}

	@Override
	public void clear(W window, TriggerContext ctx) throws Exception {
		nestedTrigger.clear(window, ctx);
	}

	@Override
	public boolean canMerge() {
		return nestedTrigger.canMerge();
	}

	@Override
	public void onMerge(W window, OnMergeContext ctx) throws Exception {
		nestedTrigger.onMerge(window, ctx);
	}

	@Override
	public String toString() {
		return "PurgingTrigger(" + nestedTrigger.toString() + ")";
	}

	/**
	 * Creates a new purging trigger from the given {@code Trigger}.
	 *
	 * @param nestedTrigger The trigger that is wrapped by this purging trigger
	 */
	public static <T, W extends Window> PurgingTrigger<T, W> of(Trigger<T, W> nestedTrigger) {
		return new PurgingTrigger<>(nestedTrigger);
	}

	@VisibleForTesting
	public Trigger<T, W> getNestedTrigger() {
		return nestedTrigger;
	}
}