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/*
 * 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.operators.async.queue;

import org.apache.flink.annotation.Internal;
import org.apache.flink.streaming.api.operators.TimestampedCollector;
import org.apache.flink.streaming.api.watermark.Watermark;
import org.apache.flink.util.Preconditions;

import javax.annotation.Nonnull;

import java.util.Collection;

/** {@link StreamElementQueueEntry} implementation for the {@link Watermark}. */
@Internal
class WatermarkQueueEntry implements StreamElementQueueEntry {
    @Nonnull private final Watermark watermark;

    WatermarkQueueEntry(Watermark watermark) {
        this.watermark = Preconditions.checkNotNull(watermark);
    }

    @Override
    public void emitResult(TimestampedCollector output) {
        output.emitWatermark(watermark);
    }

    @Nonnull
    @Override
    public Watermark getInputElement() {
        return watermark;
    }

    @Override
    public boolean isDone() {
        return true;
    }

    @Override
    public void complete(Collection result) {
        throw new IllegalStateException("Cannot complete a watermark.");
    }
}