package edu.neu.ccs.evergreen.model;

/**
 * A constraint which is a relation number and its variables.
 * 
 */
public class Constraint {
	/**
	 * The maximum rank of variables supported by the system
	 */
	public static final int MAX_RANK = 3;

	/**
	 * The unsatisfied constraint relation number.
	 */
	public static final int UNSATISFIED = 0;

	/**
	 * The satisfied constraint relation number.
	 */
	public static final int SATISFIED = 255;

	/**
	 * Can this relation be reduced at all?
	 * 
	 * @param relationNumber
	 *            Relation number to check
	 * @return True if it can not be reduced
	 */
	public static boolean reducable(int relationNumber) {
		return ((relationNumber != UNSATISFIED) && (relationNumber != SATISFIED));
	}

	private int id;

	private int relationNumber;

	private int weight;

	private int variables[];

	/**
	 * Create a new Relation Number.
	 * 
	 * @param id
	 *            ID of the constraint
	 * @param relationNumber
	 *            Relation number for the constraint
	 * @param variables
	 *            Variables in the constraint
	 * @param weight
	 *            Weight of the constraint
	 */
	public Constraint(int id, int relationNumber, int variables[], int weight) {
		this.id = id;
		this.relationNumber = relationNumber;
		verify(variables);
		this.variables = variables;
		this.weight = weight;
	}

	/**
	 * Sanity check that the variables are valid.
	 * 
	 * @param variables
	 *            Variables
	 */
	private void verify(int variables[]) {
		for (int i = 0; i < variables.length; i++) {
			for (int j = i + 1; j < variables.length; j++) {
				if (variables[i] == variables[j]) {
					throw new IllegalArgumentException("Variable "
							+ variables[i] + " is equal to " + variables[j]);
				}
			}
		}
	}

	/**
	 * Return the ID of this constraint.
	 * 
	 * @return ID
	 */
	public int getID() {
		return id;
	}

	/**
	 * Return the position of a variable in the constraint.
	 * 
	 * @param variable
	 *            Variable
	 * @return Position
	 */
	public int getPosition(int variable) {
		int position = 0;
		while (variables[position] != variable) {
			position++;
		}
		return position;
	}

	/**
	 * The relation number of this constraint.
	 * 
	 * @return Relation number
	 */
	public int getRelationNumber() {
		return relationNumber;
	}

	/**
	 * The weight of this constraint.
	 * 
	 * @return Relation weight
	 */
	public int getWeight() {
		return weight;
	}

	/**
	 * Rank of constraint.
	 * 
	 * @return Rank
	 */
	public int getRank() {
		return variables.length;
	}

	/**
	 * Return the variable at the given position.
	 * 
	 * @param position
	 *            Position
	 * @return Variable
	 */
	public int getVariable(int position) {
		return variables[position];
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		StringBuffer result = new StringBuffer();
		result.append(relationNumber);
		result.append(" ");
		result.append(weight);
		result.append(":");
		for (int i = variables.length - 1; i >= 0; i--) {
			result.append(variables[i]);
			if (i != 0) {
				result.append(" ");
			}
		}
		return result.toString();
	}
}