New Post: Decorator pattern in open source code

src/content/blog/decorator-pattern-in-open-source-code.md

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+---
+author: Erison Silva
+pubDatetime: 2024-09-27T10:00:00Z
+title: Decorator pattern in open source code
+slug: decorator-pattern-in-open-source-code
+featured: true
+draft: false
+tags:
+  - pattern
+  - developer
+description: How Decorator pattern can help us modify some functionalities from open source code.
+---
+
+In some open source repositories that contain a **small** number of maintainers are common to see classes as final, it happens because they can make modification without complex *Backward Compatibility Promise*, But on the other hand it keeps code a bit "complicated" to modify!
+
+But well it is not so complicated since they implements interfaces and use *composition* in the code 😁, and here starts the beneficial of [Decorator pattern][decorator-pattern] 💅.
+
+
+## Open source code
+
+I was looking for some project that has a good number of users, Then I choose [EasyAdminBundle][easy-admin-bundle] as example, it has more then **+18k users** and **4k starts**
+
+the piece of code that I gonna use is [AdminUrlGenerator.php][admin-url-generator], and we gonna add a dispatch event when the [generate method][admin-url-generator-method] is called.
+
+## Creating a decorator
+
+As the AdminUrlGenerator.php is a final class, it is not possible to extends this class and overite `generate` method, and in this case an alternative is use a decorator.
+
+```php
+<?php
+
+declare(strict_types = 1);
+
+namespace App\Decorator;
+
+use EasyCorp\Bundle\EasyAdminBundle\Provider\AdminContextProvider;
+use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
+use App\Event\UrlGeneratedEvent;
+
+final class AdminUrlGeneratorDecorator implements AdminContextProvider
+{
+    public function __construct(
+      private AdminUrlGenerator $adminUrlGenerator,
+      private EventDispatcherInterface $event,
+    ) {
+    }
+
+    public function generateUrl(): string
+    {
+          $url = $this->adminUrlGenerator->generate();
+          $this->event->dispatch(new UrlGeneratedEvent($url));
+
+          return $url;
+    }
+
+    public function setRoute(string $routeName, array $routeParameters = []): self
+    {
+        $this->adminUrlGenerator->setRoute($routeName, $routeParameters);
+
+        return $this;
+    }
+
+    public function get(string $paramName): mixed
+    {
+        return $this->adminUrlGenerator->get($paramName);
+    }
+
+    //....
+}
+```
+
+## Breaking Down AdminUrlGeneratorDecorator class
+
+```php
+<?php
+
+final class AdminUrlGeneratorDecorator implements AdminContextProvider
+```
+
+Here we are creating the decorator and implementing the same interface used in AdminUrlGenerator class, it is important because this class is injected via `__construct` on ClassXYZ via [AdminContextProvider][admin-context-provider-interface], and as both class implements the same interface we can choose which class we want to in inject and in our case we gonna inject the new class created (AdminUrlGeneratorDecorator)
+
+```php
+<?php
+
+    public function __construct(
+      private AdminUrlGenerator $adminUrlGenerator,
+      private EventDispatcherInterface $event,
+    ) {
+    }
+```
+
+- `AdminUrlGenerator` is the original class that we want to modify the behavour
+- `EventDispatcherInterface` is the Symofony event class, we gonna use this inside of method that we want to overite.
+
+```php
+<?php
+    public function generateUrl(): string
+    {
+          $url = $this->adminUrlGenerator->generate();
+          $this->event->dispatch(new UrlGeneratedEvent($url));
+
+          return $url;
+    }
+```
+
+It is the method that we want to modify, on the first line we are calling the original method to generate the url.
+the second line is dispatching our event and in the last one we are returning the url generated by original method.
+
+```php
+<?php
+    public function setRoute(string $routeName, array $routeParameters = []): self
+    {
+        $this->adminUrlGenerator->setRoute($routeName, $routeParameters);
+
+        return $this;
+    }
+
+    public function get(string $paramName): mixed
+    {
+        return $this->adminUrlGenerator->get($paramName);
+    }
+
+    //....
+```
+Maybe you were asking yourself, "why do I need those methods if I just want to change `generate` method?"
+
+It is needed because [AdminContextProvider][admin-context-provider-interface] is forcing to implement those methods.
+and this case we must implement them and call the original implementation, like I did with `setRoute` and `get` methods
+
+> Just to simplify the example I did not add all methods, But you must add all of them.
+
+[decorator-pattern]: https://refactoring.guru/design-patterns/decorator
+[easy-admin-bundle]: https://github.com/EasyCorp/EasyAdminBundle
+[admin-url-generator]: https://github.com/EasyCorp/EasyAdminBundle/blob/v4.12.0/src/Router/AdminUrlGenerator.php
+[admin-url-generator-method]: https://github.com/EasyCorp/EasyAdminBundle/blob/v4.12.0/src/Router/AdminUrlGenerator.php#L261
+[admin-context-provider-interface]: https://github.com/EasyCorp/EasyAdminBundle/blob/v4.12.0/src/Router/AdminUrlGeneratorInterface.php#L10