factory_method.php

<?php
abstract class ItemShop {
  public function order_item($type) {
    //$item = $this->factory->create_item($type);
    $item = $this->create_item($type);

    if ($item->is_expired()) return;
    if ($item->is_sold_out()) return;
    if ($item->on_sale()) {
      $item->sale_price();
    }
    return $item;
  }

  abstract public function create_item($type);
}



class TokyoItemShop extends ItemShop {
  public function create_item($type) {
    $item = null;
    if ($type === "katana") {
      $item = new KatanaItem();
    }
    elseif ($type === "shuriken") {
      $item = new ShurikenItem();
    }
    return $item;
  }
}


class MythlogyItemShop extends ItemShop {
  public function create_item($type) {
    $item = null;
    if ($type === "gungnir") {
      $item = new GungnirItem();
    }
    elseif ($type === "laevatein") {
      $item = new LaevateinItem();
    }
    return $item;
  }
}



abstract class Item {
  public $price;

  public function is_expired() {
    return time() > 1521767460;
  }
  public function is_sold_out() {
    return false; // infinite!
  }
  public function on_sale() {
    return false; // normal...
  }
  public function sale_price() {
    $this->price *= 0.5; // half price!
  }
}

class ShurikenItem extends Item {
  public function __construct() {
    $this->price = 100;
  }
}

class GungnirItem extends Item {
  public function __construct() {
    $this->price = 100000;
  }
}


$tokyo_item_shop = new TokyoItemShop();
$item = $tokyo_item_shop->order_item("shuriken");
echo "shuriken price: ".$item->price.PHP_EOL;

$mythology_item_shop = new MythlogyItemShop();
$item = $mythology_item_shop->order_item("gungnir");
echo "gungnir price: ".$item->price.PHP_EOL;