package bjc.utils.gen;

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;

import java.util.Random;

/**
 * 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 IList<Integer> probabilities;

	/*
	 * The list of possible results to pick from
	 */
	private IList<E> results;

	/*
	 * The source for any needed random numbers
	 */
	private Random source;

	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(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(int chance, 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() {
		IHolder<Integer> value = new Identity<>(source.nextInt(totalChance));
		IHolder<E> current = new Identity<>();
		IHolder<Boolean> picked = new Identity<>(true);

		probabilities.forEachIndexed((index, probability) -> {
			if(picked.unwrap(bool -> bool)) {
				if(value.unwrap((number) -> number < probability)) {
					current.transform((result) -> results.getByIndex(index));

					picked.transform((bool) -> false);
				} else {
					value.transform((number) -> number - probability);
				}
			}
		});

		return current.unwrap((result) -> result);
	}

	/**
	 * 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);
	}
}