Added admin notice when Imagick is not installed

gaussholder.php

@@ -19,6 +19,7 @@
 
 require_once __DIR__ . '/inc/class-plugin.php';
 require_once __DIR__ . '/inc/frontend/namespace.php';
+require_once __DIR__ . '/inc/admin/namespace.php';
 require_once __DIR__ . '/inc/jpeg/namespace.php';
 
 if ( defined( 'WP_CLI' ) && WP_CLI ) {
@@ -27,8 +28,10 @@
 }
 
 add_action( 'plugins_loaded', __NAMESPACE__ . '\\Frontend\\bootstrap' );
+add_action( 'admin_init', __NAMESPACE__ . '\\Admin\\bootstrap' );
 add_filter( 'wp_update_attachment_metadata', __NAMESPACE__ . '\\queue_generate_placeholders_on_save', 10, 2 );
 add_action( 'gaussholder.generate_placeholders', __NAMESPACE__ . '\\generate_placeholders' );
+
 // We <3 you!
 if ( WP_DEBUG && ! defined( 'WP_I_AM_A_GRUMPY_PANTS' ) ) {
 	add_action( 'admin_head-plugins.php', function () {

inc/admin/namespace.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Gaussholder\Admin;
+
+/**
+ * Set up hooked callbacks on admin_init
+ */
+function bootstrap() {
+	if ( ! current_user_can( 'manage_options' ) ) {
+		return;
+	}
+
+	if ( ! class_exists( 'Imagick' ) ) {
+		add_action( 'admin_notices', __NAMESPACE__ . '\\display_imagick_notice' );
+	}
+}
+
+/**
+ * Display a notice when Imagick PHP extension is not available.
+ */
+function display_imagick_notice() {
+	?>
+	<div class="notice notice-error">
+		<p><?php _e( 'The Imagick PHP extension is not installed. Gaussholder cannot process images without it. Please, install and activate Imagick extension.', 'gaussholder' ); ?></p>
+	</div>
+	<?php
+}