PHP: Facade

Facade

Facade is a structural design pattern that provides a simplified (but limited) interface to a complex system of classes, library or framework.

While Facade decreases the overall complexity of the application, it also helps to move unwanted dependencies to one place.

More about Facade

Application of the pattern in PHP

Complexity:

Popularity:

Usage examples: The Facade pattern is commonly used in PHP applications, where the facade classes simplify the work with complex libraries or APIs.

Example: Structure of the Pattern

This example illustrates the structure of the Facade design pattern and focuses on following questions:

  • What classes does it consists of?
  • What roles do these classes play?
  • In what way the elements of the pattern are related?

After learning about the pattern's structure it will be easier for you to grasp the following example, based on a real world PHP use case.

FacadeStructural.php: Structural Example

<?php

namespace RefactoringGuru\Facade\Structural;

/**
 * The Facade class provides a simple interface to the complex logic of one or
 * several subsystems. The Facade delegates the client requests to the
 * appropriate objects within the subsystem. The Facade is also responsible for
 * managing their lifecycle. All of this shields the client from the undesired
 * complexity of the subsystem.
 */
class Facade
{
    protected $subsystem1;

    protected $subsystem2;

    /**
     * Depending on your application's needs, you can provide the Facade with
     * existing subsystem objects or force the Facade to create them on its own.
     */
    public function __construct(
        Subsystem1 $subsystem1 = null,
        Subsystem2 $subsystem2 = null
    ) {
        $this->subsystem1 = $subsystem1 ?: new Subsystem1();
        $this->subsystem2 = $subsystem2 ?: new Subsystem2();
    }

    /**
     * The Facade's methods are convenient shortcuts to the sophisticated
     * functionality of the subsystems. However, clients get only to a fraction
     * of a subsystem's capabilities.
     */
    public function operation()
    {
        $result = "Facade initializes subsystems:\n";
        $result .= $this->subsystem1->operation1();
        $result .= $this->subsystem2->operation1();
        $result .= "Facade orders subsystems to perform the action:\n";
        $result .= $this->subsystem1->operationN();
        $result .= $this->subsystem2->operationZ();

        return $result;
    }
}

/**
 * The Subsystem can accept requests either from the facade or client directly.
 * In any case, to the Subsystem, the Facade is yet another client, and it's not
 * a part of the Subsystem.
 */
class Subsystem1
{
    function operation1()
    {
        return "Subsystem1: Ready!\n";
    }

    // ...

    function operationN()
    {
        return "Subsystem1: Go!\n";
    }
}

/**
 * Some facades can work with multiple subsystems at the same time.
 */
class Subsystem2
{
    public function operation1()
    {
        return "Subsystem2: Get ready!\n";
    }

    // ...

    public function operationZ()
    {
        return "Subsystem2: Fire!\n";
    }
}

/**
 * The client code works with complex subsystems through a simple interface
 * provided by the Facade. When a facade manages the lifecycle of the subsystem,
 * the client might not even know about the existence of the subsystem. This
 * approach lets you keep the complexity under control.
 */
function clientCode(Facade $facade)
{
    // ...

    print($facade->operation());

    // ...
}

/**
 * The client code may have some of the subsystem's objects already created. In
 * this case, it might be worthwhile to initialize the Facade with these objects
 * instead of letting the Facade create new instances.
 */
$subsystem1 = new Subsystem1();
$subsystem2 = new Subsystem2();
$facade = new Facade($subsystem1, $subsystem2);
clientCode($facade);

Output.txt: Output

Facade initializes subsystems:
Subsystem1: Ready!
Subsystem2: Get ready!
Facade orders subsystems to perform the action:
Subsystem1: Go!
Subsystem2: Fire!

Example: Real World Example

Think of the Facade as a simplicity adapter for some complex subsystem. The Facade isolates complexity within a single class and allows other application code to use the straightforward interface.

In this example, the Facade hides the complexity of the YouTube API and FFmpeg library from the client code. Instead of working with dozens of classes, the client uses a simple method on the Facade.

FacadeRealWorld.php: Real world example

<?php

namespace RefactoringGuru\Facade\RealWorld;

/**
 * Facade Design Pattern
 *
 * Intent: Provide a unified interface to a set of interfaces in a subsystem.
 * Facade defines a higher-level interface that makes the subsystem easier to
 * use.
 *
 * Example: Think of the Facade as a simplicity adapter for some complex
 * subsystem. The Facade isolates complexity within a single class and allows
 * other application code to use the straightforward interface.
 *
 * In this example, the Facade hides the complexity of the YouTube API and
 * FFmpeg library from the client code. Instead of working with dozens of
 * classes, the client uses a simple method on the Facade.
 */

/**
 * The Facade provides a single method for downloading videos from YouTube. This
 * method hides all the complexity of the PHP network layer, YouTube API and the
 * video conversion library (FFmpeg).
 */
class YouTubeDownloader
{
    protected $youtube;
    protected $ffmpeg;

    /**
     * It is handy when the Facade can manage the lifecycle of the subsystem it
     * uses.
     */
    public function __construct(string $youtubeApiKey)
    {
        $this->youtube = new YouTube($youtubeApiKey);
        $this->ffmpeg = new FFMpeg();
    }

    /**
     * The Facade provides a simple method for downloading video and encoding it
     * to a target format (for the sake of simplicity, the real-world code is
     * commented-out).
     */
    public function downloadVideo(string $url)
    {
        print("Fetching video metadata from youtube...\n");
        // $title = $this->youtube->fetchVideo($url)->getTitle();
        print("Saving video file to a temporary file...\n");
        // $this->youtube->saveAs($url, "video.mpg");

        print("Processing source video...\n");
        // $video = $this->ffmpeg->open('video.mpg');
        print("Normalizing and resizing the video to smaller dimensions...\n");
        // $video
        //     ->filters()
        //     ->resize(new FFMpeg\Coordinate\Dimension(320, 240))
        //     ->synchronize();
        print("Capturing preview image...\n");
        // $video
        //     ->frame(FFMpeg\Coordinate\TimeCode::fromSeconds(10))
        //     ->save($title . 'frame.jpg');
        print("Saving video in target formats...\n");
        // $video
        //     ->save(new FFMpeg\Format\Video\X264(), $title . '.mp4')
        //     ->save(new FFMpeg\Format\Video\WMV(), $title . '.wmv')
        //     ->save(new FFMpeg\Format\Video\WebM(), $title . '.webm');
        print("Done!\n");
    }
}

/**
 * The YouTube API subsystem.
 */
class YouTube
{
    function fetchVideo() { /* ... */ }

    function saveAs($path) { /* ... */ }

    // ...more methods and classes... RU: ...дополнительные методы и классы...
}

/**
 * The FFmpeg subsystem (a complex video/audio conversion library).
 */
class FFMpeg
{
    static public function create() { /* ... */ }

    public function open(string $video) { /* ... */ }

    // ...more methods and classes... RU: ...дополнительные методы и классы...
}

class FFMpegVideo
{
    public function filters() { /* ... */ }

    public function resize() { /* ... */ }

    public function synchronize() { /* ... */ }

    public function frame() { /* ... */ }

    public function save(string $path) { /* ... */ }

    // ...more methods and classes... RU: ...дополнительные методы и классы...
}


/**
 * The client code does not depend on any subsystem's classes. Any changes
 * inside the subsystem's code won't affect the client code. You will only need
 * to update the Facade.
 */
function clientCode(YouTubeDownloader $facade)
{
    // ...

    $facade->downloadVideo("https://www.youtube.com/watch?v=QH2-TGUlwu4");

    // ...
}

$facade = new YouTubeDownloader("APIKEY-XXXXXXXXX");
clientCode($facade);

Output.txt: Output

Fetching video metadata from youtube...
Saving video file to a temporary file...
Processing source video...
Normalizing and resizing the video to smaller dimensions...
Capturing preview image...
Saving video in target formats...
Done!