package de.ugoe.cs.cpdp.dataprocessing;

import org.apache.commons.collections4.list.SetUniqueList;

import weka.core.Instance;
import weka.core.Instances;

/**
 * Sets the bias of the weights of the training data. By using a bias of 0.5 (default value) the total weight of the positive instances (i.e.
 * fault-prone) is equal to the total weight of the negative instances (i.e. non-fault-prone). Otherwise the weights between the two will be 
 * distributed according to the bias, where <0.5 means in favor of the negative instances and >0.5 in favor of the positive instances. 
 * equal to the total weight of the test 
 * @author Steffen Herbold
 */
public class BiasedWeights implements IProcessesingStrategy, ISetWiseProcessingStrategy {

	/**
	 * bias used for the weighting
	 */
	private double bias = 0.5;
	
	
	/**
	 * Sets the bias to be used for weighting.
	 * @param parameters string with the bias
	 */
	@Override
	public void setParameter(String parameters) {
		bias = Double.parseDouble(parameters);
	}

	/**
	 * @see de.ugoe.cs.cpdp.dataprocessing.ProcessesingStrategy#apply(weka.core.Instances, weka.core.Instances)
	 */
	@Override
	public void apply(Instances testdata, Instances traindata) {
		//setBiasedWeights(testdata);
		setBiasedWeights(traindata);
	}
	
	/**
	 * @see de.ugoe.cs.cpdp.dataprocessing.SetWiseProcessingStrategy#apply(weka.core.Instances, org.apache.commons.collections4.list.SetUniqueList)
	 */
	@Override
	public void apply(Instances testdata, SetUniqueList<Instances> traindataSet) {
		for( Instances traindata : traindataSet ) {
			setBiasedWeights(traindata);
		}
	}
	
	/**
	 * Helper method that sets the weights for a given data set.
	 * @param data data set whose weights are set
	 */
	private void setBiasedWeights(Instances data) {
		final int classIndex = data.classIndex();
		
		final int[] counts = data.attributeStats(classIndex).nominalCounts;
		
		final double weightNegatives = ((1-bias)*data.numInstances()) / counts[0];
		final double weightPositives = (bias*data.numInstances()) / counts[1];
		
		
		for( int i=0 ; i<data.numInstances() ; i++ ) {
			Instance instance = data.instance(i);
			if( instance.value(classIndex)==0 ) {
				instance.setWeight(weightNegatives);
			}
			if( instance.value(classIndex)==1 ) {
				instance.setWeight(weightPositives);
			}
		}
	}

	

}