/*
 * 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.graph;

import org.apache.flink.api.common.JobExecutionResult;
import org.apache.flink.api.common.accumulators.Accumulator;
import org.apache.flink.api.common.io.RichOutputFormat;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.util.AbstractID;
import org.apache.flink.util.Preconditions;

import java.io.IOException;
import java.io.Serializable;

/**
 * A {@link GraphAnalytic} computes over a DataSet and returns the results via
 * Flink accumulators. This computation is cheaply performed in a terminating
 * {@link RichOutputFormat}.
 *
 * This class simplifies the creation of analytic helpers by providing pass-through
 * methods for adding and getting accumulators. Each accumulator name is prefixed
 * with a random string since Flink accumulators share a per-job global namespace.
 * This class also provides empty implementations of {@link RichOutputFormat#open}
 * and {@link RichOutputFormat#close}.
 *
 * @param <T> element type
 */
public abstract class AnalyticHelper<T>
extends RichOutputFormat<T> {

	private static final String SEPARATOR = "-";

	private String id = new AbstractID().toString();

	@Override
	public void configure(Configuration parameters) {}

	@Override
	public void open(int taskNumber, int numTasks) throws IOException {}

	/**
	 * Adds an accumulator by prepending the given name with a random string.
	 *
	 * @param name The name of the accumulator
	 * @param accumulator The accumulator
	 * @param <V> Type of values that are added to the accumulator
	 * @param <A> Type of the accumulator result as it will be reported to the client
	 */
	public <V, A extends Serializable> void addAccumulator(String name, Accumulator<V, A> accumulator) {
		getRuntimeContext().addAccumulator(id + SEPARATOR + name, accumulator);
	}

	/**
	 * Gets the accumulator with the given name. Returns {@code null}, if no accumulator with
	 * that name was produced.
	 *
	 * @param accumulatorName The name of the accumulator
	 * @param <A> The generic type of the accumulator value
	 * @return The value of the accumulator with the given name
	 */
	public <A> A getAccumulator(ExecutionEnvironment env, String accumulatorName) {
		JobExecutionResult result = env.getLastJobExecutionResult();

		Preconditions.checkNotNull(result, "No result found for job, was execute() called before getting the result?");

		return result.getAccumulatorResult(id + SEPARATOR + accumulatorName);
	}
}