package geniusweb.ip.general;

import java.util.Random;

public class RandomSubsetOfGivenSet {
	final private int[] givenSet;
	final private int numOfElementsInGivenSet;
	final private int sizeOfSubsetToBeSampled;
	final private boolean subsetEqualsGivenSet;
	private int[] availableIndicesToChooseFrom;
	private Random randomGenerator;

	// ******************************************************************************************************

	/**
	 * The constructor:
	 * 
	 * @param givenSet:                The set from which subsets will be
	 *                                 sampled
	 * @param numOfElementsInGivenSet: the number of elements in the set from
	 *                                 which subsets will be sampled
	 * @param sizeOfSubsetToBeSampled: the size of every subset that will be
	 *                                 sampled.
	 */
	public RandomSubsetOfGivenSet(int[] givenSet, int numOfElementsInGivenSet,
			int sizeOfSubsetToBeSampled) {
		this.givenSet = givenSet;
		this.numOfElementsInGivenSet = numOfElementsInGivenSet;
		this.sizeOfSubsetToBeSampled = sizeOfSubsetToBeSampled;
		this.randomGenerator = new Random();
		this.availableIndicesToChooseFrom = new int[numOfElementsInGivenSet];
		if (sizeOfSubsetToBeSampled == numOfElementsInGivenSet)
			subsetEqualsGivenSet = true;
		else
			subsetEqualsGivenSet = false;
	}

	// ******************************************************************************************************

	/**
	 * Returns random subset of size: "sizeOfSubsetToBeSampled", taken from the
	 * set: "givenSet"
	 */
	public int[] getSubsetInByteFormat() {
		if (this.subsetEqualsGivenSet) {
			int[] copyOfGivenSet = new int[numOfElementsInGivenSet];
			for (int i = 0; i < numOfElementsInGivenSet; i++) {
				copyOfGivenSet[i] = givenSet[i];
			}
			return copyOfGivenSet;
		} else {
			// this.randomGenerator = new Random();
			for (int i = numOfElementsInGivenSet - 1; i >= 0; i--) {
				availableIndicesToChooseFrom[i] = i;
			}
			int[] subsetInByteFormat = new int[sizeOfSubsetToBeSampled];
			int indexInSubset = 0;
			for (int i = numOfElementsInGivenSet
					- 1; i >= numOfElementsInGivenSet
							- sizeOfSubsetToBeSampled; i--) {
				int j = this.randomGenerator.nextInt(i + 1);
				subsetInByteFormat[indexInSubset] = givenSet[availableIndicesToChooseFrom[j]];
				indexInSubset++;
				availableIndicesToChooseFrom[j] = availableIndicesToChooseFrom[i];
			}
			return subsetInByteFormat;
		}
	}

	// ******************************************************************************************************

	/**
	 * Returns random subset of size: "sizeOfSubsetToBeSampled", taken from the
	 * set: "givenSet"
	 */
	public int getSubsetInBitFormat() {
		if (this.subsetEqualsGivenSet) {
			int copyOfGivenSet = 0;
			for (int i = 0; i < numOfElementsInGivenSet; i++) {
				// Add agent "givenSet[i]" to "copyOfGivenSet"
				copyOfGivenSet += 1 << (givenSet[i] - 1);
			}
			return copyOfGivenSet;
		} else {
			// this.randomGenerator = new Random();
			for (int i = numOfElementsInGivenSet - 1; i >= 0; i--) {
				availableIndicesToChooseFrom[i] = i;
			}
			int subsetInBitFormat = 0;
			int indexInSubset = 0;
			for (int i = numOfElementsInGivenSet
					- 1; i >= numOfElementsInGivenSet
							- sizeOfSubsetToBeSampled; i--) {
				int j = this.randomGenerator.nextInt(i + 1);
				// Add agent "givenSet[ availableIndicesToChooseFrom[ j ] ]" to
				// "subsetInBitFormat"
				subsetInBitFormat += 1 << (givenSet[availableIndicesToChooseFrom[j]]
						- 1);
				indexInSubset++;
				availableIndicesToChooseFrom[j] = availableIndicesToChooseFrom[i];
			}
			return subsetInBitFormat;
		}
	}
}