1 files changed, 112 insertions, 0 deletions
diff --git a/base/src/main/java/bjc/utils/gen/WeightedRandom.java b/base/src/main/java/bjc/utils/gen/WeightedRandom.java
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+++ b/base/src/main/java/bjc/utils/gen/WeightedRandom.java
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+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 final 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(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() {
+		final IHolder<Integer> value = new Identity<>(source.nextInt(totalChance));
+		final IHolder<E> current = new Identity<>();
+		final 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);
+	}
+}