package bjc.utils.gen;

import java.util.Random;

import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.Identity;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IList;

/**
 * Represents a random number generator where certain results are weighted more
 * heavily than others.
 *
 * @author ben
 *
 * @param <E>
 *        The type of values that are randomly selected.
 */
public class WeightedRandom<E> {
	/* The list of probabilities for each result */
	private final IList<Integer> probabilities;
	/* The list of possible results to pick from */
	private final IList<E> results;

	/* The source for any needed random numbers */
	private Random source;
	/* The total chance for all values. */
	private int totalChance;

	/**
	 * Create a new weighted random generator with the specified source of
	 * randomness.
	 *
	 * @param src
	 *        The source of randomness to use.
	 */
	public WeightedRandom(final Random src) {
		probabilities = new FunctionalList<>();
		results       = new FunctionalList<>();

		if(src == null) throw new NullPointerException("Source of randomness must not be null");

		source = src;
	}

	/**
	 * Add a probability for a specific result to be given.
	 *
	 * @param chance
	 *        The chance to get this result.
	 *
	 * @param result
	 *        The result to get when the chance comes up.
	 */
	public void addProbability(final int chance, final E result) {
		probabilities.add(chance);
		results.add(result);

		totalChance += chance;
	}

	/**
	 * Generate a weighted random value.
	 *
	 * @return A random value selected in a weighted fashion.
	 */
	public E generateValue() {
		return generateValue(source);
	}

	public E generateValue(Random rn) {
		int target = rn.nextInt(totalChance);

		int i = 0;

		for(int prob : probabilities) {
			if(target <= prob) return results.getByIndex(i);

			target -= prob;
			i      += 1;
		}

		throw new NullPointerException("Fell off the end of the results list");
	}
	/**
	 * Return a list of values that can be generated by this generator
	 *
	 * @return A list of all the values that can be generated
	 */
	public IList<E> getResults() {
		return results;
	}

	/**
	 * Return a list containing values that can be generated paired with the
	 * probability of those values being generated
	 *
	 * @return A list of pairs of values and value probabilities
	 */
	public IList<IPair<Integer, E>> getValues() {
		return probabilities.pairWith(results);
	}
}