Release/1.3.0 (#34)

* Fixes incorrect references to "WP_error" #1 (#29)

* Introduces find method in Loader Registry. #28 (#30)

Resolves #28

* Issue/31 - Introduce middleware API (#33)

* Moves has_trait method in Underpin class. #31

This helper method is something that can be used outside of this system. With the trend of adding methods to Underpin as static methods, it makes sense to move this method, as well.

* Introduces Middleware API. #31

* Updates Readme #31

README.md

@@ -454,23 +454,106 @@ And then register each one like so:
 
 add_action( 'init', function() {
 	$post_types    = get_post_types( [], 'objects' );
-	$ignored_types = flare_wp_get_ignored_post_types();
 
 	foreach ( $post_types as $post_type ) {
-		if ( ! in_array( $post_type->name, $ignored_types ) ) {
-			$this->shortcodes()->add( $post_type->name . '_shortcode', [
-				'class' => 'Flare_WP\Shortcodes\Post_Type_Shortcode',
-				'args'  => [ $post_type ],
-			] );
-		}
-	}
+         $this->shortcodes()->add( $post_type->name . '_shortcode', [
+             'class' => 'Flare_WP\Shortcodes\Post_Type_Shortcode',
+             'args'  => [ $post_type ],
+         ] );
+     }
 } );
 ```
 
 The key part here is how differently we handled the `add` method. Instead of simply providing a instance name, we
 instead provide an array containing the `class`, and an array of ordered `args` to pass directly into the contstructor.
 As a result, we register this class to be constructed if it is ever needed.
 
+## Middleware
+
+Some loaders support middleware. This pattern makes it possible to do a set of things when a loader item is registered.
+A good example of middleware in-action can be seen in the [script loader](https://github.com/Underpin-WP/script-loader).
+
+```php
+// Register script
+underpin()->scripts()->add( 'test', [
+        'handle'      => 'test',
+        'src'         => 'path/to/script/src',
+        'name'        => 'test',
+        'description' => 'The description',
+        'middlewares' => [
+          'Underpin_Scripts\Factories\Enqueue_Admin_Script'
+        ]
+] );
+
+// Enqueue script
+$script = underpin()->scripts()->get('test')->enqueue();
+```
+
+The above `middlewares` array would automatically cause the `test` script to be enqueued on the admin page. Multiple
+middlewares can be added in the array, and each one would run right after the item is added to the registry.
+
+The `middlewares` array uses `Underpin::make_class` to create the class instances. This means that you can pass either:
+
+1. a string that references an instance of `Script_Middleware` (see example above).
+1. An array of arguments to construct an instance of `Script_Middleware` on-the-fly (see example below).
+
+```php
+underpin()->scripts()->add( 'test', [
+	'handle'      => 'test',
+	'src'         => 'path/to/script/src',
+	'name'        => 'test',
+	'description' => 'The description',
+	'middlewares' => [
+		'Underpin_Rest_Middleware\Factories\Rest_Middleware', // Will localize script params.
+		'Underpin_Scripts\Factories\Enqueue_Script',          // Will enqueue the script on the front end all the time.
+		[                                                     // Will instantiate an instance of Script_Middleware_Instance using the provided arguments
+			'name'                => 'Custom setup params',
+			'description'         => 'Sets up custom parameters specific to this script',
+			'priority'            => 10, // Optional. Default 10.
+			'do_actions_callback' => function ( \Underpin_Scripts\Abstracts\Script $loader_item ) {
+				// Do actions
+			},
+		],
+	],
+] );
+```
+
+### Using Middleware In Your Loader
+
+The easiest way to use middleware in your loader is with the `Middleware` trait. Using the shortcode example above again:
+
+```php
+class Post_Type_Shortcode extends \Underpin\Abstracts\Shortcode {
+    use \Underpin\Traits\Middleware;
+
+	public function __construct( $post_type ) {
+		$this->shortcode = $post_type . '_is_the_best';
+
+		$this->post_type = $post_type;
+	}
+
+	public function shortcode_actions() {
+		echo $this->post_type . ' is the best post type';
+	}
+}
+```
+
+You could then register much like before, only now you can provide middleware actions.
+
+```php
+add_action( 'init', function() {
+	$post_types    = get_post_types( [], 'objects' );
+
+	foreach ( $post_types as $post_type ) {
+         $this->shortcodes()->add( $post_type->name . '_shortcode', [
+             'class'       => 'Flare_WP\Shortcodes\Post_Type_Shortcode',
+             'args'        => [ $post_type ],
+             'middlewares' => [/* Add middleware references here. */]
+         ] );
+     }
+} );
+```
+
 ## Template System Trait
 
 This plugin also includes a templating system. This system clearly separates HTML markup from business logic, and

lib/abstracts/Middleware.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * A single instance of Middleware
+ *
+ * @since   1.3.0
+ * @package Underpin\Abstracts
+ */
+namespace Underpin\Abstracts;
+
+
+use Underpin\Factories\Loader_Registry_Item;
+use Underpin\Traits\Feature_Extension;
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * Class Middleware
+ *
+ * @since   1.3.0
+ * @package Underpin\Abstracts
+ */
+abstract class Middleware {
+
+	use Feature_Extension;
+
+	/**
+	 * Loader Item
+	 *
+	 * @var Loader_Registry_Item The loader item
+	 */
+	protected $loader_item;
+
+	/**
+	 * The priority in which this middleware should be ran.
+	 *
+	 * @since 1.3.0
+	 * @var int
+	 */
+	protected $priority = 10;
+
+	/**
+	 * Sets the middleware's loader.
+	 *
+	 * @since 1.3.0
+	 *
+	 * @param Loader_Registry_Item|string|array $loader_item The loader item to set
+	 */
+	public function set_loader( $loader_item ) {
+		$this->loader_item = $loader_item;
+	}
+
+	public function __get( $key ) {
+		if ( isset( $this->$key ) ) {
+			return $this->$key;
+		} else {
+			return new \WP_Error( 'middleware_param_not_set', 'The middleware key ' . $key . ' could not be found.' );
+		}
+	}
+}

lib/abstracts/Settings_Field.php

@@ -339,7 +339,7 @@ public function __get( $key ) {
 		if ( isset( $this->$key ) ) {
 			return $this->$key;
 		} else {
-			return new WP_error( 'batch_task_param_not_set', 'The batch task key ' . $key . ' could not be found.' );
+			return new WP_Error( 'batch_task_param_not_set', 'The batch task key ' . $key . ' could not be found.' );
 		}
 	}
 

lib/abstracts/Underpin.php

@@ -585,6 +585,39 @@ protected function unsupported_actions() {
 		add_action( 'admin_notices', array( $this, 'below_version_notice' ) );
 	}
 
+	/**
+	 * Checks to see if the class, or any of its parents, uses the specified trait.
+	 *
+	 * @since 1.3.0
+	 *
+	 * @param string              $trait The trait to check for
+	 * @param object|string|false $class The class to check.
+	 * @return bool true if the class uses the specified trait, otherwise false.
+	 */
+	public static function has_trait( $trait, $class ) {
+
+		if ( false === $class ) {
+			return false;
+		}
+
+		$traits = class_uses( $class );
+
+		if ( in_array( $trait, $traits ) ) {
+			return true;
+		}
+
+		while ( get_parent_class( $class ) ) {
+			$class = get_parent_class( $class );
+
+			$has_trait = self::has_trait( $trait, $class );
+
+			if ( true === $has_trait ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
 	/**
 	 * Actions that run when this plugin meets the specified minimum requirements.
 	 *