package pacman.entries.pacman;

import pacman.utils.DataFile;

/**
 * A linear function of the feature values.
 */
public class QFunction {

	private double[] weights; // Weight vector
	private double bias; // For a constant feature
	
	private double[] eligibility; // Traces
	private double ebias; // For a constant feature
	
	/** Start with everything at zero. */
	public QFunction(FeatureSet prototype) {
		weights = new double[prototype.size()];
		eligibility = new double[prototype.size()];
	}

	/** Load initial settings from a file. */
	public QFunction(FeatureSet prototype, String filename) {
		this(prototype);
		
		DataFile file = new DataFile(filename);
		bias = Double.parseDouble(file.nextLine());
		for (int i=0; i<weights.length; i++)
			weights[i] = Double.parseDouble(file.nextLine());
		file.close();
	}

	/** Estimate the Q-value given the features for an action. */
	public double evaluate(FeatureSet features) {
		double sum = bias;
		for (int i=0; i<weights.length; i++)
			sum += (features.get(i) * weights[i]); 
		return sum;
	}

	/** Gradient-descent weight update - without eligibility traces. */
	public void updateWeights(double update, FeatureSet features) {
		for (int i=0; i<weights.length; i++)
			weights[i] += (update * features.get(i));
		bias += update;
	}
	
	/** Gradient-descent weight update - with eligibility traces. */
	public void updateWeights(double update) {
		for (int i=0; i<weights.length; i++)
			weights[i] += (update * eligibility[i]);
		bias += (update * ebias);
	}
	
	/** Zero out the eligibility traces. */
	public void clearTraces() {
		for (int i=0; i<eligibility.length; i++)
			eligibility[i] = 0;
		ebias = 0;
	}
	
	/** Decrease the eligibility traces. */
	public void decayTraces(double update) {
		for (int i=0; i<eligibility.length; i++)
			eligibility[i] *= update;
		ebias *= update;
	}
	
	/** Increase the eligibility traces. */
	public void addTraces(FeatureSet features) {
		for (int i=0; i<eligibility.length; i++)
			eligibility[i] += features.get(i);
		ebias++;
	}
	
	/** Save to a file. */
	public void save(String filename) {
		DataFile file = new DataFile(filename);
		file.clear();
		file.append(bias+"\n");
		for (double w : weights)
			file.append(w+"\n");
		file.close();
	}
}