/*
 * 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.runtime.metrics;

import org.apache.flink.metrics.Gauge;

import java.util.Arrays;

import static org.apache.flink.util.Preconditions.checkArgument;

/** A {@link Gauge} for exposing the minimum watermark of chosen {@link WatermarkGauge}s. */
public class MinWatermarkGauge implements Gauge<Long> {
    private final WatermarkGauge[] watermarkGauges;

    public MinWatermarkGauge(WatermarkGauge... watermarkGauges) {
        checkArgument(watermarkGauges.length > 0);
        this.watermarkGauges = watermarkGauges;
    }

    @Override
    public Long getValue() {
        return Arrays.stream(watermarkGauges).mapToLong(WatermarkGauge::getValue).min().orElse(0);
    }
}
