Using Exceptions for Code Flow

ImageBatchProgram.php

<?php

Class Image //Represents a single image file
{
  	public $type;	
	public $uri;

	public function __construct($pathToImage)
	{
		$this->uri = $pathToImage;		
		$this->type = getTypeFromPath($pathToImage);
	}
	
	public function loadRawData()
	{
		try
		{
			return openImageAndReadData($this->uri); //Attempt to read the image data from file
		}
		catch (FileOpenException $e) //on file error throw a Transform error
		{
			throw TransformErrorException("Image Could not be opened");
		}
	}
}

//I know this wasn't neccasary but it felt wrong creating multiple transforms and not connecting them
Interface TransformInterface
{
	public function validate($image); //This will validate the source image works with the transform
	public function process($image); //This handles the actual processing
}

Class StacheTransform implements TransformInterface
{
	public function validate($image)
	{
		return ($image->type === "PNG"); //This transform only works on PNGs
	}

	public function process($imageData)
	{
		try
		{
			return sendImageToAPI($imageData, "http://mustacheAppender.io"); //Attempt to Stache Image
		}
		catch (ServiceUnavailableException $e) //If it's a temporary error (e.g. we know the service works) try again
		{
			sleep(1);
			return $this->process($imageData);
		}
		catch (RateLimitReachedException $e) //If there is no point trying throw an error
		{
			throw TransformErrorException("Rate Limit Reached");
		}
	}
}

Class MemeTextTransform implements TransformInterface
{
	public function validate($image)
	{
		return (strpos($image->uri, "meme") === false); //You can't Meme a Meme
	}

	public function process($imageData)
	{
		try
		{
			return sendImageToAPI($imageData, "http://addMemeText.org?text=I_Has_Cheezburgers"); //Attempt to add text
		}
		catch (ServiceUnavailableException $e) //Same as before
		{
			sleep(1);
			return $this->process($imageData);
		}
		catch (ImageRejectedByMemePolice $e) //Different issue similar solution
		{
			throw TransformErrorException("Image Did not Pass Meme Quality Control");
		}
	}
}


Class ImageTransformer //Handles the processing
{
	private $images; //Images of the class above
	private $failedImages; //Associative arrays representing a failed transform

	private $transforms; //Array that holds the transforms (pretend it has one of each from above)

	public function __construct($images, $transformsArr) //Assign the images and transforms and initialize the failed array
	{
		$this->images = $imagesArr;
		$this->failedImages = array();
		$this->transforms = $transformsArr;
		$this->process(); //Call process
	}

	public function process()
	{
		foreach ($this->images as $image) { //Cycle through Images
			try
			{
				$imageData = $image->loadRawData();		
				foreach ($this->transforms as $transform) { //Cycle through transforms
					if ($transform->validate($image)) {	//Check if they validate the specific transforms test
						$imageData = $transform->process($imageData);	//transform the image storing it for the next transform to work off of
					} else { //in the event the image fails a transforms test (validate()) then throw a transform exception
						throw TransformErrorException("Image did not meet transformation's requirements");
					}
				}
				saveNewImage($imageData, $image->uri); //Save the final image on success
  			}
			catch (TransformErrorException $e) //Handle all the different transform exceptions from above
			{
				$d = (Object) array(
					"path" => $image->uri,
					"error" => $e->message
				);
				array_push($this->failedImages, $d); //Store the error for later
			}
		}

		foreach ($this->failedImages as $failed) { //Once all transforms are done, let the user know which failed and why
			echo "Image " . $failed->path . " failed transforming - Reason: " . $failed->error . "\n";
		}
	}
}