public class TelepadRegistry {

    private HashMap<Player, ArrayList<Telepad>> registeredPads;

    public void register(Player p, Telepad tp) {
        if(!registeredPads.containsKey(p)){
            //to prevent possible npe's if the HashMap doesn't have the player registered, add the player to the Map,
            //and add a new arraylist to that key index before putting the pad in the player's list.
            registeredPads.put(p, new ArrayList<Telepad>());
        }
        registeredPads.get(p).add(tp);
    }

    public Telepad getLastBuiltInRange(Telepad pad) {
        Location padLoc = pad.getLocation();
        Telepad currentChoice = pad;
        ArrayList<Telepad> inRange = getInRange(pad);
        if (inRange.isEmpty()) {
            // nothing found do nothing
        }
        else {
            currentChoice = inRange.get(0);
            double currentDiffTime = pad.getBuildTime() - currentChoice.getBuildTime();
            for (Telepad tp : inRange) {
                if(pad.getBuildTime() - tp.getBuildTime() < currentDiffTime) {
                    currentChoice = tp;
                }
            }
        }
        return currentChoice;
    }

    private ArrayList<Telepad> getInRange(Telepad source) {
        ArrayList<Telepad> retVal = new ArrayList<Telepad>();
        Location sourceLoc = source.getLocation();
        for (Telepad tp : registeredPads.get(source.getPlayerOwner())) {
            Location destLoc = tp.getLocation();
            double dx = sourceLoc.getX() - destLoc.getX();
            double dy = sourceLoc.getY() - destLoc.getY();
            double distance = Math.abs(Math.sqrt((dx * dx) + (dy * dy)));
            if (distance < source.getRange()) {
                retVal.add(tp);
            }
        }
        return retVal;
    }

}