package lab.art;

import java.util.Random;

/**
 * This utility class provides methods to create expressions.
 * 
 * @author Franck van Breugel
 */
public class Expressions 
{
    private Expressions() {}
    
    /**
     * Returns a random expression.
     * 
     * @param random a Random object.
     * @pre. random != null
     * @return a random expression.
     */
    public static Expression getRandom(Random random)
    {
	final int TYPES = 6;
	final int PRODUCT = 0;
	final int AVERAGE = 1;
	final int SINE = 2;
	final int COSINE = 3;
	final int VARIABLE_X = 4;
	final int VARIABLE_Y = 5;
	
	Expression expression;
	
	switch (random.nextInt(TYPES))
	{
	    case PRODUCT : 
		expression = new Product(Expressions.getRandom(random), Expressions.getRandom(random));
		break;
	    case AVERAGE : 
		expression = new Average(Expressions.getRandom(random), Expressions.getRandom(random));
		break;
	    case SINE : 
		expression = new Sine(Expressions.getRandom(random));
		break;
	    case COSINE : 
		expression = new Cosine(Expressions.getRandom(random));
		break;
	    case VARIABLE_X :
		expression = new VariableX();
		break;
	    case VARIABLE_Y :
		expression = new VariableY();
		break;
	    default :
		expression = null;
	}
	
	return expression;
    }
    
    /**
     * Returns the expression represented by the given string.
     * 
     * @param expression string representation of an expression.
     * @return the expression represented by the given string.
     * @throws Exception if the given string does not represent an expression.
     */
    public static Expression fromString(String expression) throws Exception
    {
	final String COS_START = "cos(pi * ";
	final String SIN_START = "sin(pi * ";
	final String AVG_START = "average(";
	final String X_START = "x";
	final String Y_START = "y";
	final String PRODUCT_START = "(";
	
	if (expression.startsWith(COS_START))
	{
	    expression = expression.substring(COS_START.length(), expression.length() - 1);
	    return new Cosine(Expressions.fromString(expression));
	}
	else if (expression.startsWith(SIN_START))
	{
	    expression = expression.substring(SIN_START.length(), expression.length() - 1);
	    return new Sine(Expressions.fromString(expression));
	}
	else if (expression.startsWith(AVG_START))
	{
	    expression = expression.substring(AVG_START.length(), expression.length() - 1);
	    int index = 0;
	    int open = 0;
	    boolean found = false;
	    while (index < expression.length() && !found)
	    {
		if (expression.charAt(index) == ',' && open == 0)
		{
		    found = true;
		}
		else if (expression.charAt(index) == '(')
		{
		    open++;
		}
		else if (expression.charAt(index) == ')')
		{
		    open--;
		}
		index++;
	    }
	    
	    if (!found)
	    {
		throw new Exception("Parsing failed");
	    }
	    else
	    {
		Expression first = Expressions.fromString(expression.substring(0, index));
		Expression second = Expressions.fromString(expression.substring(index + 1, expression.length()));
		return new Average(first, second);
	    }
	}
	else if (expression.startsWith(X_START))
	{
	    return new VariableX();
	}
	else if (expression.startsWith(Y_START))
	{
	    return new VariableY();
	}
	else if (expression.startsWith(PRODUCT_START))
	{
	    expression = expression.substring(1, expression.length() - 1);
	    int index = 0;
	    int open = 0;
	    boolean found = false;
	    while (index < expression.length() && !found)
	    {
		if (expression.charAt(index) == '*' && open == 0)
		{
		    found = true;
		}
		else if (expression.charAt(index) == '(')
		{
		    open++;
		}
		else if (expression.charAt(index) == ')')
		{
		    open--;
		}
		index++;
	    }
	    
	    if (!found)
	    {
		throw new Exception("Parsing failed");
	    }
	    else
	    {
		Expression first = Expressions.fromString(expression.substring(0, index - 1));
		Expression second = Expressions.fromString(expression.substring(index + 1, expression.length()));
		return new Product(first, second);
	    }
	}
	else
	{
	    throw new Exception("Parsing failed");
	}
    }
}