Extract a PostPusher service to push the post

Extract a `PostPusher` service with an IFTTT implementation. That means
if this needs to change to use a different service in the future, the
IFTTT implementation can remain unchanged and a new implementation can
be added with its own form params etc.

This also makes this functionality easier to test as we can add a
`NullPostPusher` implementation for testing.

References #332

web/modules/custom/blog/opdavies_blog.services.yml

@@ -10,3 +10,9 @@ services:
 
   Drupal\opdavies_blog\Repository\PostRepository:
     autowire: true
+
+  Drupal\opdavies_blog\Service\PostPusher\IftttPostPusher:
+    autowire: true
+
+  Drupal\opdavies_blog\Service\PostPusher\PostPusher:
+    alias: Drupal\opdavies_blog\Service\PostPusher\IftttPostPusher

web/modules/custom/blog/src/EventSubscriber/PushBlogPostToSocialMedia.php

@@ -4,27 +4,18 @@ declare(strict_types=1);
 
 namespace Drupal\opdavies_blog\EventSubscriber;
 
-use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Config\ImmutableConfig;
 use Drupal\core_event_dispatcher\Event\Entity\AbstractEntityEvent;
 use Drupal\hook_event_dispatcher\HookEventDispatcherInterface;
 use Drupal\opdavies_blog\Entity\Node\Post;
-use GuzzleHttp\Client;
-use GuzzleHttp\ClientInterface;
+use Drupal\opdavies_blog\Service\PostPusher\PostPusher;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
 final class PushBlogPostToSocialMedia implements EventSubscriberInterface {
 
-  private ClientInterface $client;
+  private PostPusher $postPusher;
 
-  private ImmutableConfig $config;
-
-  public function __construct(
-    ConfigFactoryInterface $configFactory,
-    Client $client
-  ) {
-    $this->client = $client;
-    $this->config = $configFactory->get('opdavies_blog.settings');
+  public function __construct(PostPusher $postPusher) {
+    $this->postPusher = $postPusher;
   }
 
   /**
@@ -49,19 +40,11 @@ final class PushBlogPostToSocialMedia implements EventSubscriberInterface {
       return;
     }
 
-    if (!$url = $this->config->get('post_tweet_webhook_url')) {
-      return;
-    }
-
     if (!$this->shouldBePushed($entity)) {
       return;
     }
 
-    $this->client->post($url, [
-      'form_params' => [
-        'value1' => $entity->toTweet(),
-      ],
-    ]);
+    $this->postPusher->push($entity);
 
     $entity->markAsSentToSocialMedia();
     $entity->save();
@@ -88,4 +71,3 @@ final class PushBlogPostToSocialMedia implements EventSubscriberInterface {
   }
 
 }
-

web/modules/custom/blog/src/Service/PostPusher/HttpPostPusher.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\opdavies_blog\Service\PostPusher;
+
+use GuzzleHttp\ClientInterface;
+
+abstract class HttpPostPusher implements PostPusher {
+
+  protected ClientInterface $client;
+
+  public function __construct(ClientInterface $client) {
+    $this->client = $client;
+  }
+
+}

web/modules/custom/blog/src/Service/PostPusher/IftttPostPusher.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\opdavies_blog\Service\PostPusher;
+
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\opdavies_blog\Entity\Node\Post;
+use GuzzleHttp\ClientInterface;
+use Webmozart\Assert\Assert;
+
+final class IftttPostPusher extends HttpPostPusher {
+
+  private ConfigFactoryInterface $configFactory;
+
+  public function __construct(
+    ClientInterface $client,
+    ConfigFactoryInterface $configFactory
+  ) {
+    $this->configFactory = $configFactory;
+
+    parent::__construct($client);
+  }
+
+  public function push(Post $post): void {
+    $url = $this->configFactory
+      ->get('opdavies_blog.settings')
+      ->get('post_tweet_webhook_url');
+
+    Assert::notNull($url, 'Cannot push the post if there is no URL.');
+
+    $this->client->post($url, [
+      'form_params' => [
+        'value1' => $post->toTweet(),
+      ],
+    ]);
+  }
+
+}

web/modules/custom/blog/src/Service/PostPusher/PostPusher.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\opdavies_blog\Service\PostPusher;
+
+use Drupal\opdavies_blog\Entity\Node\Post;
+
+interface PostPusher {
+
+  public function push(Post $post): void;
+
+}