<?php
  
  namespace Guzzle\Batch;
  
  use Guzzle\Common\Exception\InvalidArgumentException;
  
  /**
   * Batch transfer strategy where transfer logic can be defined via a Closure.
   * This class is to be used with {@see Guzzle\Batch\BatchInterface}
   */
  class BatchClosureTransfer implements BatchTransferInterface
  {
      /** @var callable A closure that performs the transfer */
      protected $callable;
  
      /** @var mixed $context Context passed to the callable */
      protected $context;
  
      /**
       * @param mixed $callable Callable that performs the transfer. This function should accept two arguments:
       *                        (array $batch, mixed $context).
       * @param mixed $context  Optional context to pass to the batch divisor
       *
       * @throws InvalidArgumentException
       */
      public function __construct($callable, $context = null)
      {
          if (!is_callable($callable)) {
              throw new InvalidArgumentException('Argument must be callable');
          }
  
          $this->callable = $callable;
          $this->context = $context;
      }
  
      public function transfer(array $batch)
      {
          return empty($batch) ? null : call_user_func($this->callable, $batch, $this->context);
      }
  }