gilded rose - php - step before polymorphism

GildedRose.php

<?php

namespace GildedRose;

class GildedRose
{

    private $items;

    function __construct($items)
    {
        $this->items = $items;
    }

    function updateQuality()
    {
        foreach ($this->items as $item) {
            $this->updateItem($item);
        }
    }

    /**
     * @param $item
     */
    private function updateItem($item)
    {
        if ($item->name == 'Sulfuras, Hand of Ragnaros') {
            return;
        }

        $item->sell_in = $item->sell_in - 1;

        switch ($item->name) {
            case 'Aged Brie' :
                if ($item->quality < 50) {
                    $increase = 1;
                    if ($item->sell_in < 0) {
                        $increase++;
                    }
                    $item->quality = $item->quality + $increase;
                }
                break;
            case 'Backstage passes to a TAFKAL80ETC concert':
                if ($item->quality < 50) {
                    $increase = 1;
                    if ($item->sell_in < 10) {
                        $increase++;
                    }
                    if ($item->sell_in < 5) {
                        $increase++;
                    }
                    $item->quality = $item->quality + $increase;
                }
                if ($item->sell_in < 0) {
                    $item->quality = 0;
                }
                break;
            default:
                if ($item->quality > 0) {
                    $decrease = 1;
                    if ($item->sell_in < 0) {
                        $decrease++;
                    }
                    $item->quality = $item->quality - $decrease;
                }
                break;

        }
    }
}