package edu.neu.ccs.evergreen.model;

import java.util.Set;

/**
 * Used to capture how a value was assigned to a variable.
 */
public class Assignment {
	private int variable;

	private int value;

	private boolean decision;

	private Set<Integer> forcedBy;

	private Constraint forcingConstraint;

	/**
	 * Create a simple assignment that attaches a value to a variable.
	 * 
	 * @param variable
	 *            Variable
	 * @param value
	 *            Value
	 */
	public Assignment(int variable, int value) {
		this(variable, value, true, null, null);
	}

	/**
	 * Create a complex assignment that tracks what variables forced the
	 * variable to the set and the constraint the caused it to be forced.
	 * 
	 * @param variable
	 *            Variable
	 * @param value
	 *            Value
	 * @param forcedBy
	 *            Variables that forced it
	 * @param forcingConstraint
	 *            Constraint that did the forcing
	 */
	public Assignment(int variable, int value, Set<Integer> forcedBy,
			Constraint forcingConstraint) {
		this(variable, value, false, forcedBy, forcingConstraint);
	}

	/**
	 * An assignment of a value to a variable. This also indicates if the
	 * assignment was forced or was a decision variable.
	 * 
	 * @param variable
	 *            Variable
	 * @param value
	 *            Value
	 * @param decision
	 *            True if decided
	 */
	private Assignment(int variable, int value, boolean decision,
			Set<Integer> forcedBy, Constraint forcingConstraint) {
		if (variable < 0) {
			throw new IllegalArgumentException("Variable must be positive");
		}
		this.variable = variable;
		this.value = value;
		this.decision = decision;
		this.forcedBy = forcedBy;
		this.forcingConstraint = forcingConstraint;
	}

	/**
	 * Return the variable for use in creating a super resolvent. This will
	 * reverse its value if it was a decision variable otherwise it returns it
	 * as is.
	 * 
	 * @return Signed negated variable
	 */
	public int getForcedVariable() {
		if (!decision) {
			return variable;
		}
		if (value == 0) {
			return variable;
		}
		return -variable;
	}

	/**
	 * Raw variable.
	 * 
	 * @return Variable
	 */
	public int getVariable() {
		return variable;
	}

	/**
	 * Value assigned to the variable.
	 * 
	 * @return Value
	 */
	public int getValue() {
		return value;
	}
	
	/**
	 * Was this a decision variable.
	 * 
	 * @return True if decision; false otherwise
	 */
	public boolean getDecision() {
		return decision;
	}

	/**
	 * Set if this was a decision variable.
	 * 
	 * @param decision
	 *            True if a decision variable
	 */
	public void setDecision(boolean decision) {
		this.decision = decision;
	}

	/**
	 * Return the variables that forced this variable to be set.
	 * 
	 * @return Forcing variables
	 */
	public Set<Integer> getForcedBy() {
		return forcedBy;
	}

	/**
	 * Return the constraint that caused the variable to be forced.
	 * 
	 * @return Constraint
	 */
	public Constraint getForcingConstraint() {
		return forcingConstraint;
	}

	/**
	 * Add a set of variables to those that caused the forcing.
	 * 
	 * @param forcedBy
	 *            Forced by
	 */
	public void addForcedBy(Set<Integer> forcedBy) {
		this.forcedBy.addAll(forcedBy);
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		StringBuffer result = new StringBuffer();
		result.append(variable);
		if (decision) {
			result.append("*");
		}
		result.append("=");
		result.append(value);
		return result.toString();
	}
}