package tmcsim.highwaymodel;

import java.util.Comparator;

/**
 * Compare two stations by route and postmile. 
 * Used by Highways.toJson() so json is listed by route then postmile
 * @author jdalbey
 * @version 4/2/2019
 */
public final class StationComparator implements Comparator
{

    /**
     * Compare two stations by route and postmile. 
     */
    @Override
    public int compare(Object a, Object b)
    {
        // check for identity
        if (a == b)
        {
            return 0;
        }
        // check that Object is of type Station, if not throw exception
        if (!(a instanceof Station && b instanceof Station))
        {
            throw new ClassCastException("A Station object expected.");
        }
        Station statA = (Station) a;
        Station statB = (Station) b;
        // compare by direction field first
        int i = statA.direction.compareTo(statB.direction);
        if (i != 0) return i;
        
        // get difference of postmile values
        double val = statA.postmile - statB.postmile;
        
        // set appropriate comparable return value
        int retval = 0;
        if (val > 0)
        {
            retval = 1;
        }
        else if (val < 0)
        {
            retval = -1;
        }

        return retval;
    }

}