package lab.art;

/**
 * This class represents a binary expression.
 * 
 * @author Franck van Breugel
 */
public abstract class BinaryExpression extends Expression 
{
    private Expression first;
    private Expression second;
    //@ invariant this.first != null && this.second != null
    
    /**
     * Initializes this binary expression with the given two subexpressions.
     * 
     * @param first the first subexpression.
     * @pre. first != null
     * @param second the second subexpression.
     * @pre. second != null
     */
    public BinaryExpression(Expression first, Expression second) 
    {
	super();
	this.setFirst(first);
	this.setSecond(second);
    }
    
    /**
     * Returns the first subexpression of this binary expression.
     * 
     * @return the first subexpression of this binary expression.
     */
    private Expression getFirst() 
    {
	return this.first;
    }

    /**
     * Returns the second subexpression of this binary expression.
     * 
     * @return the second subexpression of this binary expression.
     */
    private Expression getSecond() 
    {
	return this.second;
    }

    /**
     * Sets the first subexpression of this binary expression to the given expression.
     * 
     * @param first the new first subexpression of this binary expression.
     */
    private void setFirst(Expression first) 
    {
	this.first = first;
    }

    /**
     * Sets the second subexpression of this binary expression to the given expression.
     * 
     * @param second the new second subexpression of this binary expression.
     */
    private void setSecond(Expression second) 
    {
	this.second = second;
    }
    
    /**
     * Tests whether this binary expression is the same as the given object.
     * Two binary expressions are the same if their subexpressions are the same,
     * that is, the first expression of the one is equal to the first expression
     * of the other and the second expression of the one is equal to the second
     * expression of the other, or the first expression of the one is equal to 
     * the second expression of the other and the second expression of the one 
     * is equal to the first expression of the other.
     * 
     * @param object an object.
     * @return true if this binary expression is the same as the given object,
     * false otherwise.
     */
    public boolean equals(Object object)
    {
	boolean equal;
	if (object != null && this.getClass() == object.getClass())
	{
	    BinaryExpression other = (BinaryExpression) object;
	    equal = (this.getFirst().equals(other.getFirst()) &&
		     this.getSecond().equals(other.getSecond())) ||
		(this.getFirst().equals(other.getSecond()) &&
		 this.getSecond().equals(other.getFirst()));
	}
	else
	{
	    equal = false;
	}
	return equal;
    }
    
    /**
     * Returns the hash code of this binary expression.
     * The hash code of a binary expression is the sum
     * of the hash codes of its subexpressions.
     * 
     * @return the hash code of this binary expression.
     */
    public int hashCode()
    {
	return this.getFirst().hashCode() + this.getSecond().hashCode();
    }
    
    /**
     * Evaluates this binary expression at the given x- and y-coordinate
     * with the given binary operator.
     * 
     * @param x the x-coordinate.
     * @pre. x >= -1 && x <= 1
     * @param y the y-coordinate.
     * @pre. y >= -1 && y <= 1
     * @param operator a binary operator.
     * @pre. operator != null
     * @return the value of this binary expression at the given x- and y-coordinate
     * with the given binary operator.
     */
    public double evaluate(double x, double y, BinaryOperator operator)
    {
	return operator.operation(this.getFirst().evaluate(x, y), this.getSecond().evaluate(x, y));
    }
    
    /**
     * Returns a string representation of this binary expression for the given pattern.
     * 
     * @param pattern the pattern describing how the two subexpressions should be combined.
     * @pre. pattern contains %s twice
     * @return a string representation of this binary expression for the given pattern.
     */
    public String toString(String pattern)
    {
	return String.format(pattern, this.getFirst().toString(), this.getSecond().toString());
    }
}