package franck.eecs1030;

import java.util.HashMap;
import java.util.Map;

/**
 * Converts amounts between different units.
 * 
 * @author Franck van Breugel
 */
public class Converter
{
    /**
     * The constant that represents the unit of centimeters.
     */
    public static final int CENTIMETER = 1;
    
    /**
     * The constant that represents the unit of feet.
     */
    public static final int FOOT = 4;
    
    /**
     * The constant that represents the unit of inches.
     */
    public static final int INCH = 3;
    
    /**
     * The constant that represents the unit of meters.
     */
    public static final int METER = 2;
    
    private static Map<Integer, Map<Integer, Double>> factor = new HashMap<Integer, Map<Integer, Double>>();
    
    static
    {
	final double CENTIMETERS_PER_METER = 100.0;
	final double CENTIMETERS_PER_INCH = 2.54;
	final double CENTIMETERS_PER_FOOT = 30.48;
	final double INCHES_PER_FOOT = 12.0;
	
	Map<Integer, Double> map = new HashMap<Integer, Double>();
	
	map.put(Converter.CENTIMETER, 1.0);
	map.put(Converter.METER, 1.0 / CENTIMETERS_PER_METER);
	map.put(Converter.INCH, 1.0 / CENTIMETERS_PER_INCH);
	map.put(Converter.FOOT, 1.0 / CENTIMETERS_PER_FOOT);
	Converter.factor.put(Converter.CENTIMETER, map);
	
	map = new HashMap<Integer, Double>();
	map.put(Converter.CENTIMETER, CENTIMETERS_PER_METER);
	map.put(Converter.METER, 1.0);
	map.put(Converter.INCH, CENTIMETERS_PER_METER / CENTIMETERS_PER_INCH);
	map.put(Converter.FOOT, CENTIMETERS_PER_METER / CENTIMETERS_PER_FOOT);
	Converter.factor.put(Converter.METER, map);
	
	map = new HashMap<Integer, Double>();
	map.put(Converter.CENTIMETER, CENTIMETERS_PER_INCH);
	map.put(Converter.METER, CENTIMETERS_PER_INCH / CENTIMETERS_PER_METER);
	map.put(Converter.INCH, 1.0);
	map.put(Converter.FOOT, 1.0 / INCHES_PER_FOOT);
	Converter.factor.put(Converter.INCH, map);
	
	map = new HashMap<Integer, Double>();
	map.put(Converter.CENTIMETER, CENTIMETERS_PER_FOOT);
	map.put(Converter.METER, CENTIMETERS_PER_FOOT / CENTIMETERS_PER_METER);
	map.put(Converter.INCH, INCHES_PER_FOOT);
	map.put(Converter.FOOT, 1.0);
	Converter.factor.put(Converter.FOOT, map);
    }
    
    private Converter() {}
    
    /**
     * Converts the given amount from the given unit to the other given unit.
     * 
     * @param amount the amount to be converted.
     * @pre. amount >= 0
     * @param from the unit of the amount.
     * @pre. from == Converter.CENTIMETER || from == Converter.METER || from == Converter.INCH || from == Converter.FOOT
     * @param to the unit to which the amount is converted.
     * @pre. to == Converter.CENTIMETER || to == Converter.METER || to == Converter.INCH || to == Converter.FOOT
     * @return the given amount converted from the given unit to the other given unit.
     * @throws IllegalArgumentException if the amount is too big so that it causes an overflow.
     */
    public static double convert(double amount, int from, int to) throws IllegalArgumentException
    {
	double converted = amount * Converter.factor.get(from).get(to);
	
	if (converted == Double.POSITIVE_INFINITY) // overflow
	{
	    throw new IllegalArgumentException();
	}
	else
	{
	    return converted;
	}
    }
}