xpto.php

<?php
class Xpto
{	
	public function addPoints($amount)
	{
		return $this->processPoints($amount, function ($amount, $currentPointsAvailable, $conversionRate) {
			return $currentPointsAvailable + ($amount * $conversionRate)
		});
	}

	public function removePoints($amount)
	{
	    return $this->processPoints($amount, function ($amount, $currentPointsAvailable, $conversionRate) {
			return $currentPointsAvailable - ($amount * $conversionRate)
		});
	}

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

		if (!is_callable($action)) {
			throw new InvalidArgument('Action must be a callable');
		}
		$newPoints = $action($amount, $currentPointsAvailable, $conversionRate);

        // SAVE THE PORRA TODA!
	}
}