Introduce Abstract_Admin_Page class.

Author: Felix Arntz

composer.json

@@ -27,7 +27,8 @@
     }
   },
   "require": {
-    "php": ">=7.0"
+    "php": ">=7.0",
+    "brightnucleus/config": "~0.4"
   },
   "require-dev": {
     "codeclimate/php-test-reporter": "dev-master",

src/Admin_Page/Abstract_Admin_Page.php

@@ -0,0 +1,116 @@
+<?php
+/**
+ * Abstract_Admin_Page class
+ *
+ * @package Leaves_And_Love\OOP_Admin_Pages\Admin_Page
+ * @since 1.0.0
+ */
+
+namespace Leaves_And_Love\OOP_Admin_Pages\Admin_Page;
+
+use Leaves_And_Love\OOP_Admin_Pages\Admin_Page;
+use Leaves_And_Love\OOP_Admin_Pages\Exception\Config_Invalid_Exception;
+use BrightNucleus\Config\ConfigInterface as Config;
+use BrightNucleus\Config\ConfigTrait;
+
+/**
+ * Abstract class representing an admin page.
+ *
+ * @since 1.0.0
+ */
+abstract class Abstract_Admin_Page implements Admin_Page {
+
+	use ConfigTrait;
+
+	const SLUG                = 'slug';
+	const TITLE               = 'title';
+	const RENDER_CALLBACK     = 'render_callback';
+	const INITIALIZE_CALLBACK = 'initialize_callback';
+
+	/**
+	 * Constructor.
+	 *
+	 * Sets the configuration.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @param Config $config Admin page configuration. Must contain keys 'slug' (admin page identifier), 'title'
+	 *                       and 'render_callback' (callable that receives the configuration as sole parameter).
+	 *                       May also contain an 'initialize_callback' key.
+	 *
+	 * @throws Config_Invalid_Exception Thrown when the configuration is invalid.
+	 */
+	public function __construct( Config $config ) {
+		$this->processConfig( $config );
+
+		$required_keys = $this->get_required_config_keys();
+
+		foreach ( $required_keys as $required_key ) {
+			if ( ! $this->hasConfigKey( $required_key ) ) {
+				throw new Config_Invalid_Exception( sprintf( 'The required configuration key %s is missing.', $required_key ) );
+			}
+
+			$value = $this->getConfigKey( $required_key );
+			if ( empty( $value ) ) {
+				throw new Config_Invalid_Exception( sprintf( 'The required configuration key %s is empty.', $required_key ) );
+			}
+		}
+	}
+
+	/**
+	 * Gets the slug of the admin page.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return string Admin page slug.
+	 */
+	public function get_slug() : string {
+		return $this->getConfigKey( self::SLUG );
+	}
+
+	/**
+	 * Gets the title of the admin page.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return string Admin page title.
+	 */
+	public function get_title() : string {
+		return $this->getConfigKey( self::TITLE );
+	}
+
+	/**
+	 * Initializes the admin page on pageload.
+	 *
+	 * This method must be called before any output is printed.
+	 *
+	 * @since 1.0.0
+	 */
+	public function initialize() {
+		if ( ! $this->hasConfigKey( self::INITIALIZE_CALLBACK ) ) {
+			return;
+		}
+
+		call_user_func( $this->getConfigKey( self::INITIALIZE_CALLBACK ), $this->config );
+	}
+
+	/**
+	 * Renders the admin page content.
+	 *
+	 * @since 1.0.0
+	 */
+	public function render() {
+		call_user_func( $this->getConfigKey( self::RENDER_CALLBACK ), $this->config );
+	}
+
+	/**
+	 * Gets the configuration keys that are required for an admin page.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return array Array of configuration keys.
+	 */
+	protected function get_required_config_keys() {
+		return array( self::SLUG, self::TITLE, self::RENDER_CALLBACK );
+	}
+}

src/Exception/Config_Invalid_Exception.php

@@ -0,0 +1,20 @@
+<?php
+/**
+ * Config_Invalid_Exception class
+ *
+ * @package Leaves_And_Love\OOP_Admin_Pages\Exception
+ * @since 1.0.0
+ */
+
+namespace Leaves_And_Love\OOP_Admin_Pages\Exception;
+
+use Exception;
+
+/**
+ * Exception thrown when a configuration is invalid.
+ *
+ * @since 1.0.0
+ */
+class Config_Invalid_Exception extends Exception {
+
+}