BackupHandler

BackupPowerDelegateInteface.php

<?php

interface BackupPowerDelegateInteface

   public function successTurnonPowerBackup();
   public function successTurnonPowerBackup();
}

BackupPowerHandler.php

<?php

class BackupPowerHandler
{
   /**
    * @var BackupPowerDelegateInteface
    */
   protected $delegate;

   public function setDelegate(BackupPowerDelegateInteface $delegate)
   {
       $this->delegate = $delegate;
   }

   public function turnOnPower()
   {
       $turnedOn = rand(0, 1);

       if($turnedOn)
           $this->delegate->successTurnonPowerBackup();
       else $this->delegate->errorTurnonPowerBackup();
   }
}

OfficeDelegate.php

<?php

class OfficeDelegate implements PrintingDelegate, BackupPowerDelegateInterface
{

    /**
     * @var BackupPowerHandler
     */
    private $backupHandler;

    /**
     * @var PrinterHandler
     */
    private $printer;

    /**
     * OfficeDelegate constructor.
     *
     * @param $backupHandler
     * @param $printer
     */
    public function __construct(BackupPowerHandler $backupPowerHandler, PrinterHandler $printer)
    {
        $this->backupHandler = $backupPowerHandler;
        $this->printer       = $printer;
    }


    public function process()
    {
        $printingHandler = new PrinterHandler($this);
        $printingHandler->printDocument();

        if (!$this->turnOnPower()) {
            $backupPowerHandler = new BackupPowerHandler();
            $backupPowerHandler->setDelegate($this);
            $backupPowerHandler->turnOnPower();
        }
    }

    /**
     * @return boolean
     */
    private function turnOnPower()
    {
        return boolval(rand(0, 1));
    }

    /**
     * Implement method to receive printing document from printer
     *
     * @param array $documents
     */
    public function pickPrintingDocument(array $documents)
    {
        foreach ($documents as $doc) {
            echo 'Received document: ' . $doc;
        }
    }

    public function successTurnonPowerBackup()
    {
        echo 'Power is turned on successfully';
    }

    public function errorTurnonPowerBackup()
    {
        throw new Exception('Can not turn on backup power!');
    }
}

PrinterHandler.php

<?php

class PrinterHandler
{
    /**
     * @var PrintingDelegate
     */
    private $delegate;

    public function __construct($delegate = null)
    {
        if ($delegate) {
            $this->delegate = $delegate;
        }
    }

    public function setDelegate(PrintingDelegate $delegate)
    {
        $this->delegate = $delegate;
    }


    private function chargeInk()
    {
        echo 'Charging ink';
    }

    public function printDocument()
    {
        $this->chargeInk();
        $documents = [];

        for ($i = 0; $i < 10; $i++) {
            $documents[$i] = 'Document ' . $i;
        }
        $this->delegate->pickPrintingDocument($documents);
    }
}

PrintingDelegateInterface.php

<?php

interface PrintingDelegateInterface
{

    public function pickPrintingDocument(array $documents);
}