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/**
 * Copyright (C) 2016 Hurence ([email protected])
 *
 * 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 com.hurence.logisland.sampling;

import com.hurence.logisland.record.Record;

import java.util.List;
import java.util.stream.Collectors;

public class FirstItemSampler extends AbstractSampler {


    private int numBuckets;

    public FirstItemSampler(String valueFieldName, String timeFieldName, int numBuckets) {
        super(valueFieldName,timeFieldName);
        this.numBuckets = numBuckets;
    }


    /**
     * divide the points sequence into equally sized buckets
     * and select the first point of each bucket
     *
     * @param inputRecords the iput list
     * @return
     */
    @Override
    public List sample(List inputRecords) {
        // simple downsample to numBucket data points
        final int bucketSize = SamplingUtils.fitBucketSize(inputRecords, numBuckets);

        return SamplingUtils.grouped(inputRecords, bucketSize)
                .map(record -> getTimeValueRecord(record.get(0)))
                .collect(Collectors.toList());
    }
}