wayang-platforms/wayang-spark/src/main/java/org/apache/wayang/spark/compiler/ExtendedFlatMapFunctionAdapter.java

/*
 * 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.spark.compiler;

import org.apache.spark.api.java.function.FlatMapFunction;
import org.apache.spark.api.java.function.Function;
import org.apache.wayang.core.function.ExecutionContext;
import org.apache.wayang.core.function.FunctionDescriptor;
import org.apache.wayang.spark.execution.SparkExecutionContext;

import java.util.Iterator;

/**
 * Implements a {@link FlatMapFunction} that calls {@link org.apache.wayang.core.function.ExtendedFunction#open(ExecutionContext)}
 * of its implementation before delegating the very first {@link Function#call(Object)}.
 */
public class ExtendedFlatMapFunctionAdapter<InputType, OutputType> implements FlatMapFunction<InputType, OutputType> {

    private final FunctionDescriptor.ExtendedSerializableFunction<InputType, Iterable<OutputType>> impl;

    private final SparkExecutionContext executionContext;

    private boolean isFirstRun = true;

    public ExtendedFlatMapFunctionAdapter(FunctionDescriptor.ExtendedSerializableFunction extendedFunction,
                                          SparkExecutionContext sparkExecutionContext) {
        this.impl = extendedFunction;
        this.executionContext = sparkExecutionContext;
    }

    @Override
    public Iterator<OutputType> call(InputType v1) throws Exception {
        if (this.isFirstRun) {
            this.impl.open(this.executionContext);
            this.isFirstRun = false;
        }

        return this.impl.apply(v1).iterator();
    }

}