How to use a strategy design pattern in Magento2?

What is a strategy design pattern?

Strategy pattern is known as Policy Pattern also.

The Strategy design pattern allows you to take a class that does something specific in a lot of different ways and extracts all of these algorithms into separate classes called strategies.

Use a strategy design pattern to avoid writing multiple if else statements or switch cases to perform some event.

Example:- If you want to trigger a custom notification after placing an order according to order status so to perform this event you have to use multiple if else statements or switch cases and you have to write extra lines of code to do your task to call the method for each state. use the strategy design pattern to perform this task by writing a few lines of code in place of multiple if-else statements or switch cases.

How to use the strategy pattern

1) Create file etc/frontend/di.xml in your module to define the order status and methods. Those you want to call according to order status.

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Webkul\Custom\Helper\Data">
        <arguments>
            <argument name="orderStatus" xsi:type="array">
                <item name="order_status" xsi:type="array">
                    <item name="new" xsi:type="string">newState</item>
                    <item name="processing" xsi:type="string">processingState</item>
                    <item name="holded" xsi:type="string">holdedState</item>
                    <item name="canceled" xsi:type="string">canceledState</item>
                    <item name="complete" xsi:type="string">completeState</item>
                </item>
            </argument>
        </arguments>
    </type>
</config>

Use the type declaration to add the arguments in your class constructor parameters.

2) Create \Helper\Data.php in your module as we have defined the type “Webkul\Custom\Helper\Data” in di.xml. We are using the helper to load the arguments. So we can use it all over the class as per requirements.

<?php

namespace Webkul\Custom\Helper;

/**
 * MpNotifications data helper
 */
class Data extends \Magento\Framework\App\Helper\AbstractHelper
{

    /**
     * Construct
     *
     * @param \Magento\Framework\App\Helper\Context $context
     * @param array $orderStatus
     */
    public function __construct(
        \Magento\Framework\App\Helper\Context $context,
        $orderStatus = []
    ) {
        parent::__construct($context);
        $this->orderStatus = $orderStatus;
    }


    /**
     * Return method array
     *
     * @param string $type
     * @return array
     */
    public function getMethodArray($type)
    {
        return $this->orderStatus[$type];
    }

}

3) Create file Webkul\Custom\Observer\SalesOrderChangeStateAfterObserver.php for the event sales_order_save_after

<?php

namespace Webkul\Custom\Observer;

use Magento\Framework\Event\ObserverInterface;

class SalesOrderChangeStateAfterObserver implements ObserverInterface
{
    public const ORDER_STATUS = 'order_status';

    /**
     * @var $_ordersFactory
     */
    protected $_ordersFactory;

    /**
     * Constructor
     *
     * @param \Magento\Sales\Model\OrdersFactory $ordersFactory
     * @param \Webkul\Custom\Helper\Data $dataHelper
     */
    public function __construct(               \Magento\Sales\Model\OrdersFactory $ordersFactory,
        \Webkul\Custom\Helper\Data $dataHelper
    ) {
        $this->_ordersFactory = $ordersFactory;
        $this->_dataHelper = $dataHelper;
    }

    /**
     * Sales Order Change State After
     *
     * @param \Magento\Framework\Event\Observer $observer
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {        
          try {
                        $order = $observer->getEvent()->getOrder();
                    
                        $orderId = $order->getId();
                        $orderFactory = $this->_ordersFactory->create();
                        $methodArray = $this->_dataHelper->getMethodArray(self::ORDER_STATUS);
                        if (!empty($order->getState())) {
                            $method = $methodArray[$order->getState()];
                            $this->$method($orderId, $order, $orderFactory);
                        }
            }
    }

    /**
     * New state
     *
     * @param int $orderId
     * @param object $order
     * @param object $orderFactory
     */
    private function newState($orderId, $order, $orderFactory)
    {
      // Wrrite your code here
    }

}