OXDEV-8947 Add decoration example

Signed-off-by: Anton Fedurtsya <anton@fedurtsya.com>

Author: Sieg

README.md

@@ -94,6 +94,9 @@ The repository contains examples of following cases and more:
 
 * [Using Symfony DI](services.yaml)
   * [Injection of Registry classes with bind](https://github.com/OXID-eSales/examples-module/blob/b-7.4.x/services.yaml#L16)
+  * [Service decoration](src/Greeting/Service/Decorator/GreetingValidationDecorator.php) - shows how to decorate services
+    * Note: While the example uses validation/truncation for simplicity, better use cases include logging, caching, performance monitoring, or audit trails
+    * [Decorator registration](src/Greeting/services.yaml) - using `decorates:` in DI configuration
 
 * [Migrations](migration)
   * extending a shop database table (`oxuser`)

src/Greeting/Service/Decorator/GreetingValidationDecorator.php

@@ -0,0 +1,58 @@
+<?php
+
+/**
+ * Copyright © . All rights reserved.
+ * See LICENSE file for license details.
+ */
+
+declare(strict_types=1);
+
+namespace OxidEsales\ExamplesModule\Greeting\Service\Decorator;
+
+use OxidEsales\Eshop\Application\Model\User as EshopModelUser;
+use OxidEsales\ExamplesModule\Greeting\Service\GreetingMessageServiceInterface;
+
+/**
+ * Decorator that adds validation to greeting messages.
+ *
+ * This is an example of the Decorator pattern in Symfony DI.
+ * Decorators allow you to add cross-cutting concerns (like validation,
+ * logging, caching) without modifying the original service.
+ *
+ * Benefits:
+ * - Open/Closed Principle: extend functionality without modifying existing code
+ * - Single Responsibility: validation logic separate from business logic
+ * - Easy to enable/disable: just register/unregister the decorator
+ * - Testable: can test validation independently
+ */
+readonly class GreetingValidationDecorator implements GreetingMessageServiceInterface
+{
+    private const MAX_GREETING_LENGTH = 50;
+
+    public function __construct(
+        private GreetingMessageServiceInterface $originalService
+    ) {
+    }
+
+    public function getGeneralGreeting(): string
+    {
+        return $this->originalService->getGeneralGreeting();
+    }
+
+    public function getGreeting(?EshopModelUser $user = null): string
+    {
+        return $this->originalService->getGreeting($user);
+    }
+
+    /**
+     * Truncates greeting message if it exceeds maximum length before saving.
+     */
+    public function saveGreetingForCurrentUser(string $message): void
+    {
+        if (mb_strlen($message) > self::MAX_GREETING_LENGTH) {
+            $message = mb_substr($message, 0, self::MAX_GREETING_LENGTH);
+        }
+
+        $this->originalService->saveGreetingForCurrentUser($message);
+    }
+}

src/Greeting/services.yaml

@@ -16,6 +16,11 @@ services:
       $shopName: '%env(OEEM_SHOP_NAME)%'
     public: true
 
+  OxidEsales\ExamplesModule\Greeting\Service\Decorator\GreetingValidationDecorator:
+    decorates: OxidEsales\ExamplesModule\Greeting\Service\GreetingMessageServiceInterface
+    arguments:
+      $originalService: '@.inner'
+
   OxidEsales\ExamplesModule\Greeting\Service\UserServiceInterface:
     class: OxidEsales\ExamplesModule\Greeting\Service\UserService
 

tests/Unit/Greeting/Service/Decorator/GreetingValidationDecoratorTest.php

@@ -0,0 +1,106 @@
+<?php
+
+/**
+ * Copyright © . All rights reserved.
+ * See LICENSE file for license details.
+ */
+
+declare(strict_types=1);
+
+namespace OxidEsales\ExamplesModule\Tests\Unit\Greeting\Service\Decorator;
+
+use OxidEsales\Eshop\Application\Model\User;
+use OxidEsales\ExamplesModule\Greeting\Service\Decorator\GreetingValidationDecorator;
+use OxidEsales\ExamplesModule\Greeting\Service\GreetingMessageServiceInterface;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(GreetingValidationDecorator::class)]
+final class GreetingValidationDecoratorTest extends TestCase
+{
+    #[Test]
+    public function getGeneralGreetingDelegatesToInnerService(): void
+    {
+        $expectedGreeting = uniqid('greeting');
+        $innerService = $this->createMock(GreetingMessageServiceInterface::class);
+        $innerService->expects($this->once())
+            ->method('getGeneralGreeting')
+            ->willReturn($expectedGreeting);
+
+        $sut = $this->getSut(originalService: $innerService);
+
+        $this->assertSame($expectedGreeting, $sut->getGeneralGreeting());
+    }
+
+    #[Test]
+    public function getGreetingDelegatesToInnerService(): void
+    {
+        $expectedGreeting = uniqid('greeting');
+        $userMock = $this->createMock(User::class);
+
+        $innerService = $this->createMock(GreetingMessageServiceInterface::class);
+        $innerService->expects($this->once())
+            ->method('getGreeting')
+            ->with($userMock)
+            ->willReturn($expectedGreeting);
+
+        $sut = $this->getSut(originalService: $innerService);
+
+        $this->assertSame($expectedGreeting, $sut->getGreeting($userMock));
+    }
+
+    #[Test]
+    #[DataProvider('truncationProvider')]
+    public function saveGreetingForCurrentUserTruncatesLongMessages(
+        string $inputMessage,
+        string $expectedMessage
+    ): void {
+        $innerService = $this->createMock(GreetingMessageServiceInterface::class);
+        $innerService->expects($this->once())
+            ->method('saveGreetingForCurrentUser')
+            ->with($expectedMessage);
+
+        $sut = $this->getSut(originalService: $innerService);
+        $sut->saveGreetingForCurrentUser($inputMessage);
+    }
+
+    public static function truncationProvider(): array
+    {
+        return [
+            'exactly 50 chars' => [
+                str_repeat('a', 50),
+                str_repeat('a', 50),
+            ],
+            'exactly 51 chars - truncated to 50' => [
+                str_repeat('a', 51),
+                str_repeat('a', 50),
+            ],
+            'long message - 100 chars truncated to 50' => [
+                str_repeat('a', 100),
+                str_repeat('a', 50),
+            ],
+            'message with multibyte chars' => [
+                'Это очень длинное приветствие которое должно быть обрезано',
+                'Это очень длинное приветствие которое должно быть ',
+            ],
+            'short message passed through' => [
+                'Hello',
+                'Hello',
+            ],
+            'empty string passed through' => [
+                '',
+                '',
+            ],
+        ];
+    }
+
+    private function getSut(
+        ?GreetingMessageServiceInterface $originalService = null
+    ): GreetingValidationDecorator {
+        return new GreetingValidationDecorator(
+            originalService: $originalService ?? $this->createStub(GreetingMessageServiceInterface::class)
+        );
+    }
+}