Creating Filters

This chapter explains how to create your own file filters using AbstractFileFilter.

Preparation

You need to install the package rekalogika/file-derivation to use this feature:

composer require rekalogika/file-derivation

To create a filter class, you can extend AbstractFileFilter, create a method (or more) for the callers to specify the filtering parameters, and implement all the abstract methods.

The following is an example filter class that creates a derived file by (rather uselessly) appending a text to the original content:

use Rekalogika\Contracts\File\FileInterface;
use Rekalogika\File\Derivation\Filter\AbstractFileFilter;
use Rekalogika\File\TemporaryFile;

class TextAppender extends AbstractFileFilter
{
    private string $text;

    /**
     * Your custom method that lets the caller specify the filtering parameters.
     */
    public function appendText(string $text): self
    {
        assert(ctype_alpha($text)); // ensure alpha characters only
        $this->text = $text;

        return $this;
    }

    /**
     * This method return the derivation ID from the filtering parameters the
     * caller provided.
     */
    #[\Override]
    protected function getDerivationId(): string
    {
        return 'append_' . $this->text;
    }

    #[\Override]
    protected function process(): FileInterface
    {
        $originalContent = $this->getSourceFile()->getContent();

        return new TemporaryFile::createFromString($originalContent . $this->text);
    }
}

If you are using autoconfiguration, then you are all set. Otherwise, you need to tag your class with rekalogika.file.derivation.filter:

config/services.yaml

services:
    App\TextAppender:
        tags:
            - { name: 'rekalogika.file.derivation.filter' }

A caller will be able to use the above filter like the following:

use Rekalogika\Contracts\File\FileInterface;

/** @var TextAppender $textAppender */
/** @var FileInterface $file */

$derivedFile = $textAppender
    ->take($file)
    ->appendText('foo')
    ->getResult();