package edu.neu.ccs.evergreen.model;

/**
 * Used to create constraint.
 * 
 */
public class ConstraintFactory {
	private static int BASE[] = new int[Constraint.MAX_RANK + 1];

	static {
		for (int rank = 0; rank < BASE.length; rank++) {
			BASE[rank] = (int) Math.pow(2, Math.pow(2, rank)) - 1;
		}
	}

	/**
	 * Create an or constraint with rank 1, 2, or 3.
	 * 
	 * @param id
	 *            ID of the constraint
	 * @param relationNumber
	 *            Relation for the constraint
	 * @param variables
	 *            Variables in the relation
	 * @param weight
	 *            Weight of relation
	 * @return Relation Number
	 */
	public static Constraint createConstraint(int id, int relationNumber,
			int variables[], int weight) {
		if (variables.length > Constraint.MAX_RANK) {
			throw new IllegalArgumentException("Vars can not be longer than "
					+ Constraint.MAX_RANK);
		}
		if ((relationNumber < Constraint.UNSATISFIED)
				|| (relationNumber > Constraint.SATISFIED)) {
			throw new IllegalArgumentException("Relation number "
					+ relationNumber + " is not valid.");
		}
		return new Constraint(id, relationNumber, variables, weight);
	}

	/**
	 * Create an or constraint with rank 1, 2, or 3.
	 * 
	 * @param id
	 *            ID of the constraint
	 * @param variables
	 *            Variables in the relation
	 * @param weight
	 *            Weight of relation
	 * @return Relation Number
	 */
	public static Constraint createOr(int id, int variables[], int weight) {
		if (variables.length > Constraint.MAX_RANK) {
			throw new IllegalArgumentException("Vars can not be longer than "
					+ Constraint.MAX_RANK);
		}
		int missing = 1;
		int offset = 1;
		for (int i = 0; i < variables.length; i++) {
			if (variables[i] < 0) {
				variables[i] = -variables[i];
				missing = missing << offset;
			}
			offset *= 2;
		}
		int relationNumber = BASE[variables.length] & ~missing;
		for (int i = variables.length; i < Constraint.MAX_RANK; i++) {
			relationNumber = relationNumber | relationNumber << offset;
			offset *= 2;
		}
		return new Constraint(id, relationNumber, variables, weight);
	}

	/**
	 * Create an implies constraint such that 1 or 2 implies 0.
	 * 
	 * @param id
	 *            ID of the constraint
	 * @param variables
	 *            Three variables
	 * @param weight
	 *            Weight of relation
	 * @return Relation Number
	 */
	public static Constraint createImplies(int id, int variables[], int weight) {
		if (variables.length != 3) {
			throw new IllegalArgumentException("Vars must be of length 3");
		}
		int relationNumber = 169;
		if (variables[1] < 0) {
			variables[1] = -variables[1];
			if (variables[2] < 0) {
				variables[2] = -variables[2];
				relationNumber = 106;
			} else {
				relationNumber = 166;
			}
		} else if (variables[2] < 0) {
			variables[2] = -variables[2];
			relationNumber = 154;
		}
		return new Constraint(id, relationNumber, variables, weight);
	}
}