/*
 * 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.flink.operators;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.functions.KeySelector;
import org.apache.wayang.basic.operators.ReduceByOperator;
import org.apache.wayang.core.api.Configuration;
import org.apache.wayang.core.function.ReduceDescriptor;
import org.apache.wayang.core.function.TransformationDescriptor;
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.flink.channels.DataSetChannel;
import org.apache.wayang.flink.compiler.FunctionCompiler;
import org.apache.wayang.flink.execution.FlinkExecutor;


/**
 * Flink implementation of the {@link ReduceByOperator}.
 */
public class FlinkReduceByOperator<InputType, KeyType>
        extends ReduceByOperator<InputType, KeyType>
        implements FlinkExecutionOperator {


    /**
     * Creates a new instance.
     *
     * @param type             type of the reduce elements (i.e., type of {@link #getInput()} and {@link #getOutput()})
     * @param keyDescriptor    describes how to extract the key from data units
     * @param reduceDescriptor describes the reduction to be performed on the elements
     */
    public FlinkReduceByOperator(DataSetType<InputType> type, TransformationDescriptor<InputType, KeyType> keyDescriptor,
                                 ReduceDescriptor<InputType> reduceDescriptor) {
        super(keyDescriptor, reduceDescriptor, type);
    }

    /**
     * Copies an instance (exclusive of broadcasts).
     *
     * @param that that should be copied
     */
    public FlinkReduceByOperator(ReduceByOperator<InputType, KeyType> that) {
        super(that);
    }

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

        DataSetChannel.Instance input = (DataSetChannel.Instance) inputs[0];
        DataSetChannel.Instance output = (DataSetChannel.Instance) outputs[0];

        final DataSet<InputType> dataSetInput = input.provideDataSet();

        FunctionCompiler compiler = flinkExecutor.getCompiler();

        KeySelector<InputType, KeyType> keySelector = compiler.compileKeySelector(this.keyDescriptor);

        ReduceFunction<InputType> reduceFunction = compiler.compile(this.reduceDescriptor);


        DataSet<InputType> dataSetOutput =
                dataSetInput
                        .groupBy(keySelector)
                        .reduce(reduceFunction)
                        .setParallelism(flinkExecutor.getNumDefaultPartitions());

        output.accept(dataSetOutput, flinkExecutor);

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

    @Override
    protected ExecutionOperator createCopy() {
        return new FlinkReduceByOperator<>(this.getType(), this.getKeyDescriptor(), this.getReduceDescriptor());
    }


    @Override
    public String getLoadProfileEstimatorConfigurationKey() {
        return "wayang.flink.reduceby.load";
    }

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

    @Override
    public List<ChannelDescriptor> getSupportedInputChannels(int index) {
        return Arrays.asList(DataSetChannel.DESCRIPTOR, DataSetChannel.DESCRIPTOR_MANY);
    }

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

    @Override
    public boolean containsAction() {
        return false;
    }
}