/*
 * 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.java.operators;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.function.BinaryOperator;
import org.apache.wayang.basic.operators.GlobalReduceOperator;
import org.apache.wayang.core.api.Configuration;
import org.apache.wayang.core.function.ReduceDescriptor;
import org.apache.wayang.core.optimizer.OptimizationContext;
import org.apache.wayang.core.optimizer.costs.LoadProfileEstimator;
import org.apache.wayang.core.optimizer.costs.LoadProfileEstimators;
import org.apache.wayang.core.plan.wayangplan.ExecutionOperator;
import org.apache.wayang.core.platform.ChannelDescriptor;
import org.apache.wayang.core.platform.ChannelInstance;
import org.apache.wayang.core.platform.lineage.ExecutionLineageNode;
import org.apache.wayang.core.types.DataSetType;
import org.apache.wayang.core.util.Tuple;
import org.apache.wayang.java.channels.CollectionChannel;
import org.apache.wayang.java.channels.JavaChannelInstance;
import org.apache.wayang.java.channels.StreamChannel;
import org.apache.wayang.java.execution.JavaExecutor;

/**
 * Java implementation of the {@link GlobalReduceOperator}.
 */
public class JavaGlobalReduceOperator<Type>
        extends GlobalReduceOperator<Type>
        implements JavaExecutionOperator {


    /**
     * Creates a new instance.
     *
     * @param type             type of the reduce elements (i.e., type of {@link #getInput()} and {@link #getOutput()})
     * @param reduceDescriptor describes the reduction to be performed on the elements
     */
    public JavaGlobalReduceOperator(DataSetType<Type> type,
                                    ReduceDescriptor<Type> reduceDescriptor) {
        super(reduceDescriptor, type);
    }

    /**
     * Copies an instance (exclusive of broadcasts).
     *
     * @param that that should be copied
     */
    public JavaGlobalReduceOperator(GlobalReduceOperator<Type> that) {
        super(that);
    }

    @Override
    public Tuple<Collection<ExecutionLineageNode>, Collection<ChannelInstance>> evaluate(
            ChannelInstance[] inputs,
            ChannelInstance[] outputs,
            JavaExecutor javaExecutor,
            OptimizationContext.OperatorContext operatorContext) {
        assert inputs.length == this.getNumInputs();
        assert outputs.length == this.getNumOutputs();

        final BinaryOperator<Type> reduceFunction = javaExecutor.getCompiler().compile(this.reduceDescriptor);
        JavaExecutor.openFunction(this, reduceFunction, inputs, operatorContext);

        final Optional<Type> reduction = ((JavaChannelInstance) inputs[0]).<Type>provideStream().reduce(reduceFunction);
        ((CollectionChannel.Instance) outputs[0]).accept(reduction.isPresent() ?
                Collections.singleton(reduction.get()) :
                Collections.emptyList());

        return ExecutionOperator.modelEagerExecution(inputs, outputs, operatorContext);
    }

    @Override
    public String getLoadProfileEstimatorConfigurationKey() {
        return "wayang.java.globalreduce.load";
    }

    @Override
    public Optional<LoadProfileEstimator> createLoadProfileEstimator(Configuration configuration) {
        final Optional<LoadProfileEstimator> optEstimator =
                JavaExecutionOperator.super.createLoadProfileEstimator(configuration);
        LoadProfileEstimators.nestUdfEstimator(optEstimator, this.reduceDescriptor, configuration);
        return optEstimator;
    }

    @Override
    public List<ChannelDescriptor> getSupportedInputChannels(int index) {
        assert index <= this.getNumInputs() || (index == 0 && this.getNumInputs() == 0);
        if (this.getInput(index).isBroadcast()) return Collections.singletonList(CollectionChannel.DESCRIPTOR);
        return Arrays.asList(CollectionChannel.DESCRIPTOR, StreamChannel.DESCRIPTOR);
    }

    @Override
    public List<ChannelDescriptor> getSupportedOutputChannels(int index) {
        assert index <= this.getNumOutputs() || (index == 0 && this.getNumOutputs() == 0);
        return Collections.singletonList(CollectionChannel.DESCRIPTOR);
    }

}