bigtop-master/bigtop-data-generators/bigpetstore-data-generator/src/main/java/org/apache/bigtop/datagenerators/bigpetstore/generators/transaction/CategoryWeightFunction.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.bigtop.datagenerators.bigpetstore.generators.transaction;

import org.apache.bigtop.datagenerators.samplers.pdfs.ExponentialPDF;
import org.apache.bigtop.datagenerators.samplers.pdfs.ProbabilityDensityFunction;
import org.apache.bigtop.datagenerators.samplers.wfs.ConditionalWeightFunction;
import org.apache.bigtop.datagenerators.samplers.wfs.WeightFunction;

public class CategoryWeightFunction implements ConditionalWeightFunction<Double, Double>
{
	private final ProbabilityDensityFunction<Double> pdf;

	public CategoryWeightFunction(double averagePurchaseTriggerTime)
	{
		double lambda = 1.0 / averagePurchaseTriggerTime;
		pdf = new ExponentialPDF(lambda);
	}

	@Override
	public double weight(Double exhaustionTime, Double transactionTime)
	{
		double remainingTime = Math.max(0.0, exhaustionTime - transactionTime);
		return pdf.probability(remainingTime);
	}
}
