xpto.php

<?php
class Xpto
{	
	public function addPoints($amount)
	{
        return $this->addOrRemovePoints($amount, 'add');
	}

	public function removePoints($amount)
	{
	    return $this->addOrRemovePoints($amount, 'remove');
	}

	private function addOrRemovePoints($amount, $action)
	{
	    $currentPointsAvailable = (float)$this->get('points_available');
	    $conversionRate = (float)$this->get('points_per_base_ccy_unit');

	    switch ($action) {
            case 'add':
                $newPoints = $currentPointsAvailable + ($amount * $conversionRate);
                break;
            case 'remove':
                $newPoints = $currentPointsAvailable - ($amount * $conversionRate);
                break;
            default:
                throw new Exception('Invalid call to this method.');
	    }

        // SAVE THE PORRA TODA!
	}
}