/*
 * 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.wayang.basic.operators;

import org.apache.wayang.core.api.Configuration;
import org.apache.wayang.core.function.FunctionDescriptor;
import org.apache.wayang.core.function.ReduceDescriptor;
import org.apache.wayang.core.optimizer.cardinality.CardinalityEstimator;
import org.apache.wayang.core.optimizer.cardinality.FixedSizeCardinalityEstimator;
import org.apache.wayang.core.plan.wayangplan.UnaryToUnaryOperator;
import org.apache.wayang.core.types.DataSetType;

import java.util.Optional;

/**
 * This operator is context dependent: after a {@link GroupByOperator}, it is meant to be a {@link ReduceByOperator};
 * otherwise, it is a {@link GlobalReduceOperator}.
 */
public class ReduceOperator<Type> extends UnaryToUnaryOperator<Type, Type> {

    private final ReduceDescriptor<Type> reduceDescriptor;

    /**
     * @deprecated This method is just a hack that is necessary because of the ambiguous nature of this operator.
     */
    public static <Type> ReduceOperator<Type> createGroupedReduce(
            ReduceDescriptor<Type> reduceDescriptor,
            DataSetType<? extends Iterable<Type>> inputType,
            DataSetType<Type> outputType) {
        return new ReduceOperator<>(reduceDescriptor, (DataSetType<Type>) inputType, outputType);
    }

    /**
     * Creates a new instance.
     *
     * @param reduceDescriptor describes the reduction to be performed by this operator
     */
    public ReduceOperator(ReduceDescriptor<Type> reduceDescriptor,
                          DataSetType<Type> inputType, DataSetType<Type> outputType) {
        super(inputType, outputType, true);
        this.reduceDescriptor = reduceDescriptor;
    }


    /**
     * Creates a new instance.
     *
     * @param reduceDescriptor describes the reduction to be performed by this operator
     */
    public ReduceOperator(FunctionDescriptor.SerializableBinaryOperator<Type> reduceDescriptor,
                          Class<Type> typeClass) {
        this(new ReduceDescriptor<>(reduceDescriptor, typeClass),
                DataSetType.createDefault(typeClass),
                DataSetType.createDefault(typeClass));
    }


    public ReduceDescriptor<Type> getReduceDescriptor() {
        return this.reduceDescriptor;
    }

    @Override
    public Optional<CardinalityEstimator> createCardinalityEstimator(int outputIndex,
                                                                     Configuration configuration) {
        return Optional.of(new FixedSizeCardinalityEstimator(1L));
    }
}