Gilded Rose kata

gistfile1.php

<?php

require_once 'src/Item.php';

class GildedRose {

    const DEFAULT_QUALITY_CHANGE = -1;
    const DEGRADES_TWICE_AS_FAST = 2;
    const DEFAULT_CHANGE_FOR_BACKSTAGE_PASS = 1;
    const CHANGE_FOR_BACKSTAGE_PASS_WHEN_LESS_THAN_5_DAYS = 3;
    const CHANGE_FOR_BACKSTAGE_PASS_WHEN_LESS_THAN_10_DAYS = 2;
    const MAXIMUM_QUALITY_VALUE = 50;
    const MINIMUM_QUALITY_VALUE = 0;

    public static function updateQuality($items) {
       foreach($items as $item) {

            $qualityChange = self::getQualityChange($item);
            $item->setQuality($item->getQuality() + $qualityChange);
            if($item->getQuality() > self::MAXIMUM_QUALITY_VALUE) {
                $item->setQuality(self::MAXIMUM_QUALITY_VALUE);
            }
            if($item->getQuality() < self::MINIMUM_QUALITY_VALUE) {
                $item->setQuality(self::MINIMUM_QUALITY_VALUE);
            }

            $sellInChange = -1;
            if($item->name == "Sulfuras, Hand of Ragnaros") {
                $sellInChange = 0;
            }
            $item->setSellIn($item->getSellIn() + $sellInChange);

        } 
    }

    private static function getQualityChange($item) {
        $change = self::DEFAULT_QUALITY_CHANGE;
        $change = self::modifyQualityBasedOnItemType($item,$change);
        $change = self::modifyQualityBasedOnSellIn($item,$change);
        if($item->name == "Backstage passes to a TAFKAL80ETC concert") {
            $change = self::countBackstagePassQuality($item);
        }
        return $change;
    }
    
    private static function modifyQualityBasedOnItemType($item,$change) {
        switch ($item->getName()) {
            case "Aged Brie":
                return abs($change);
            case "Sulfuras, Hand of Ragnaros":
                return 0;
            case "Conjured Mana Cake":
                return $change * 2;
            default:
                return $change;
        }
    }

    private static function modifyQualityBasedOnSellIn($item,$change) {
        if($item->getSellIn() <= 0) {
            return $change * self::DEGRADES_TWICE_AS_FAST;
        }
        return $change;
    }

    private static function countBackstagePassQuality($item) {
        if($item->getSellIn() <= 0) {
            return -$item->getQuality();
        }       
        if($item->getSellIn() <= 5) {
            return self::CHANGE_FOR_BACKSTAGE_PASS_WHEN_LESS_THAN_5_DAYS;
        }       
        if($item->getSellIn() <= 10) {
            return self::CHANGE_FOR_BACKSTAGE_PASS_WHEN_LESS_THAN_10_DAYS;
        }       
 
        return self::DEFAULT_CHANGE_FOR_BACKSTAGE_PASS;
    }

}