/*******************************************************************************
 * Copyright (c) 2015-2018 Skymind, Inc.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Apache License, Version 2.0 which is available at
 * https://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.
 *
 * SPDX-License-Identifier: Apache-2.0
 ******************************************************************************/

package org.datavec.spark.transform.sparkfunction.sequence;

import lombok.AllArgsConstructor;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.sql.Row;
import org.datavec.api.transform.schema.Schema;
import org.datavec.api.writable.Writable;
import org.datavec.spark.transform.DataFrames;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * Combiner function for use in {@link DataFrames#toRecordsSequence(DataFrame)}
 * <p>
 * Assumption here: first two columns are the sequence UUID and the sequence index, as per
 * {@link DataFrames#toDataFrameSequence(Schema, JavaRDD)}
 *
 * @author Alex Black
 */
@AllArgsConstructor
public class DataFrameToSequenceMergeValue
                implements Function2<List<List<Writable>>, Iterable<Row>, List<List<Writable>>> {

    private final Schema schema;

    @Override
    public List<List<Writable>> call(List<List<Writable>> seqSoFar, Iterable<Row> rows) throws Exception {
        List<List<Writable>> retSeq = new ArrayList<>(seqSoFar);
        for (Row v1 : rows) {
            List<Writable> ret = DataFrames.rowToWritables(schema, v1);
            retSeq.add(ret);
        }

        Collections.sort(retSeq, new Comparator<List<Writable>>() {
            @Override
            public int compare(List<Writable> o1, List<Writable> o2) {
                return Integer.compare(o1.get(1).toInt(), o2.get(1).toInt());
            }
        });

        return retSeq;
    }
}
