/**
 * Code originally by Ahmed Abdel Mohsen
 * Code modified by Daniel Rinehart <danielr@neophi.com>
 * Original version at https://www.ccs.neu.edu/course/csg260/ssl/RelationReduction/
 */
/**
 * Utility class used to work with relation clauses that are of rank three and
 * represent truth tables between 0 and 255.
 */
class Relation1 {
	/**
	 * Private constructor to force utility class usage.
	 */
	private Relation1() {
	}

	/**
	 * Reduce the relation by setting the variable in the location specified by
	 * variableNumber to value.
	 * 
	 * @param relationNumber
	 *            Current relation number
	 * @param variableNumber
	 *            Variable number to set
	 * @param value
	 *            Value to set variable to
	 * @return Reduced relation number
	 */
	public static int reduce(int relationNumber, int variableNumber, int value) {
		int r, m; // new relation number
		m = getMagicNumber(variableNumber, value);
		r = (relationNumber & m);
		if (value == 0) {
			r = r | (r << (1 << variableNumber));
		} else {
			r = r | (r >> (1 << variableNumber));
		}
		return r;
	}

	/**
	 * Determine if a variable is still in a relation.
	 * 
	 * @param relationNumber
	 *            Relation to check
	 * @param variableNumber
	 *            Variable position to check
	 * @return True if the variable is still in the relation
	 */
	public static boolean isVariableNotInRelation(int relationNumber, int variableNumber) {
		int r0 = reduce(relationNumber, variableNumber, 0);
		int r1 = reduce(relationNumber, variableNumber, 1);
		return (r0 == r1);
	}

	/**
	 * Determine how many variables are still in a relation.
	 * 
	 * @param relationNumber
	 *            Relation to check
	 * @return Number of variables in relation
	 */
	public static int variablesInRelation(int relationNumber) {
		int rank = 3;
		for (int i = 0; i < 3; i++) {
			if (isVariableNotInRelation(relationNumber, i)) {
				rank--;
			}
		}
		return rank;
	}

	/**
	 * Determine how many rows in the relation's truth table evaluate to true
	 * given s variables set to true.
	 * 
	 * @param relationNumber
	 *            Relation to check
	 * @param sub
	 *            Number of variables set to true
	 * @return Number of rows that evaluate to true
	 */
	public static int q(int relationNumber, int sub/* 0,1,2,3 */) {
		int m;
		switch (sub) {
		case 0:
			m = 1;
			break;
		case 1:
			m = 22;
			break;
		case 2:
			m = 104;
			break;
		case 3:
			m = 128;
			break;
		default:
			m = 0;
			System.out.println("Sub can be 0,1,2,or 3");
		}
		return ones((relationNumber & m));
	}

	/**
	 * Determine the total number of rows in the relation's truth table that
	 * evaluate to true.
	 * 
	 * @param relationNumber
	 *            Relation check
	 * @return Number of rows that evaluate to true.
	 */
	public static int ones(int relationNumber) {
		int c = 0;
		for (int i = 0; i < 8; i++) {
			if ((relationNumber & (1 << i)) != 0) {
				c++;
			}
		}
		return c;
	}

	/**
	 * Determine the magic number for a variable position and value.
	 * 
	 * @param variableNumber
	 *            Variable position
	 * @param value
	 *            Value
	 * @return Magic number
	 */
	private static int getMagicNumber(int variableNumber, int value) {
		// ToDo: use xor, see if there is a default return value
		if (value == 0) {
			if (variableNumber == 0) {
				return 85; /* 1st var (Least Significant), value 0 */
			}
			if (variableNumber == 1) {
				return 51;
			}
			if (variableNumber == 2) {
				return 15; /* last var (Most Significant), value 0 */
			}
			System.out.println("Only 3 variable Numbers are allowed 0,1,2");
		} else if (value == 1) {
			if (variableNumber == 0) {
				return 170; /* 1st var (Least Significant), value 1 */
			}
			if (variableNumber == 1) {
				return 204;
			}
			if (variableNumber == 2) {
				return 240; /* last var (Most Significant), value 0 */
			}
			System.out.println("Only 3 variable Numbers are allowed 0,1,2");
		} else {
			System.out.println("Only 0 or 1 are allowed as values");
		}
		return -1;
	}
}