/*
 * 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.flink.api.java.operators;

import org.apache.flink.annotation.Public;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.util.Preconditions;

/**
 * Base class for operations that operates on two input data sets.
 * 
 * @param <IN1> The data type of the first input data set.
 * @param <IN2> The data type of the second input data set.
 * @param <OUT> The data type of the returned data set.
 */
@Public
public abstract class TwoInputOperator<IN1, IN2, OUT, O extends TwoInputOperator<IN1, IN2, OUT, O>> extends Operator<OUT, O> {
	
	private final DataSet<IN1> input1;
	private final DataSet<IN2> input2;
	
	
	protected TwoInputOperator(DataSet<IN1> input1, DataSet<IN2> input2, TypeInformation<OUT> resultType) {
		super(Preconditions.checkNotNull(input1, "input1 is null").getExecutionEnvironment(), resultType);
		Preconditions.checkNotNull(input2, "input2 is null");
		DataSet.checkSameExecutionContext(input1, input2);
		this.input1 = input1;
		this.input2 = input2;
	}
	
	/**
	 * Gets the data set that this operation uses as its first input.
	 * 
	 * @return The data set that this operation uses as its first input.
	 */
	public DataSet<IN1> getInput1() {
		return this.input1;
	}
	
	/**
	 * Gets the data set that this operation uses as its second input.
	 * 
	 * @return The data set that this operation uses as its second input.
	 */
	public DataSet<IN2> getInput2() {
		return this.input2;
	}
	
	/**
	 * Gets the type information of the data type of the first input data set.
	 * This method returns equivalent information as {@code getInput1().getType()}.
	 * 
	 * @return The first input data type.
	 */
	public TypeInformation<IN1> getInput1Type() {
		return this.input1.getType();
	}
	
	/**
	 * Gets the type information of the data type of the second input data set.
	 * This method returns equivalent information as {@code getInput2().getType()}.
	 * 
	 * @return The second input data type.
	 */
	public TypeInformation<IN2> getInput2Type() {
		return this.input2.getType();
	}
	
	/**
	 * Translates this java API operator into a common API operator with two inputs.
	 * 
	 * @param input1 The first input of the operation, as a common API operator.
	 * @param input2 The second input of the operation, as a common API operator.
	 * @return The created common API operator.
	 */
	protected abstract org.apache.flink.api.common.operators.Operator<OUT> translateToDataFlow(
			org.apache.flink.api.common.operators.Operator<IN1> input1, org.apache.flink.api.common.operators.Operator<IN2> input2);
}