Added publication-embed shortcode.

includes/shortcodes/abstract-shortcode.php

@@ -0,0 +1,47 @@
+<?php
+/**
+ * @package CleverOgre
+ * @subpackage OgreIssuu
+ * @version 0.1.0
+ * @since 0.1.0
+ */
+
+namespace OgreIssuu\Shortcodes;
+
+defined('ABSPATH') || exit;
+
+use OgreIssuu\Singleton;
+
+abstract class Shortcode {
+    use Singleton;
+
+    public function __construct() {
+        $this->register();
+    }
+
+    protected function get_tag():string {
+        $parts = explode('\\', get_called_class());
+        return sanitize_key(preg_replace('/([a-z])([A-Z])/', '$1-$2', array_pop($parts)));
+    }
+
+    protected function register():void {
+        add_shortcode($this->get_tag(), [$this, 'callback']);
+    }
+    
+    public function get_default_attributes():array {
+        return [];
+    }
+
+    public function get_attributes(array $atts = []):array {
+        return shortcode_atts($this->get_default_attributes(), $atts, $this->get_tag());
+    }
+
+    public function callback(array $atts, ?string $content = null) {
+        ob_start();
+        $this->render($this->get_attributes($atts), (!is_null($content) ? $content : ''));
+        return ob_get_clean();
+    }
+
+    public abstract function render(array $atts, string $content):void;
+
+}