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    <h3>Editing: AccessiblePrivateMethods.php</h3>
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namespace Automattic\WooCommerce\Internal\Traits;

use Automattic\WooCommerce\Utilities\ArrayUtil;

/**
 * This trait allows making private methods of a class accessible from outside.
 * This is useful to define hook handlers with the [$this, 'method'] or [__CLASS__, 'method'] syntax
 * without having to make the method public (and thus having to keep it forever for backwards compatibility).
 *
 * Example:
 *
 * class Foobar {
 *   use AccessiblePrivateMethods;
 *
 *   public function __construct() {
 *     self::add_action('some_action', [$this, 'handle_some_action']);
 *   }
 *
 *   public static function init() {
 *     self::add_filter('some_filter', [__CLASS__, 'handle_some_filter']);
 *   }
 *
 *   private function handle_some_action() {
 *   }
 *
 *   private static function handle_some_filter() {
 *   }
 * }
 *
 * For this to work the callback must be an array and the first element of the array must be either '$this', '__CLASS__',
 * or another instance of the same class; otherwise the method won't be marked as accessible
 * (but the corresponding WordPress 'add_action' and 'add_filter' functions will still be called).
 *
 * No special procedure is needed to remove hooks set up with these methods, the regular 'remove_action'
 * and 'remove_filter' functions provided by WordPress can be used as usual.
 */
trait AccessiblePrivateMethods {

	//phpcs:disable PSR2.Classes.PropertyDeclaration.Underscore
	/**
	 * List of instance methods marked as externally accessible.
	 *
	 * @var array
	 */
	private $_accessible_private_methods = array();

	/**
	 * List of static methods marked as externally accessible.
	 *
	 * @var array
	 */
	private static $_accessible_static_private_methods = array();
	//phpcs:enable PSR2.Classes.PropertyDeclaration.Underscore

	/**
	 * Register a WordPress action.
	 * If the callback refers to a private or protected instance method in this class, the method is marked as externally accessible.
	 *
	 * $callback can be a standard callable, or a string representing the name of a method in this class.
	 *
	 * @param string          $hook_name       The name of the action to add the callback to.
	 * @param callable|string $callback        The callback to be run when the action is called.
	 * @param int             $priority        Optional. Used to specify the order in which the functions
	 *                                         associated with a particular action are executed.
	 *                                         Lower numbers correspond with earlier execution,
	 *                                         and functions with the same priority are executed
	 *                                         in the order in which they were added to the action. Default 10.
	 * @param int             $accepted_args   Optional. The number of arguments the function accepts. Default 1.
	 */
	protected static function add_action( string $hook_name, $callback, int $priority = 10, int $accepted_args = 1 ): void {
		self::process_callback_before_hooking( $callback );
		add_action( $hook_name, $callback, $priority, $accepted_args );
	}

	/**
	 * Register a WordPress filter.
	 * If the callback refers to a private or protected instance method in this class, the method is marked as externally accessible.
	 *
	 * $callback can be a standard callable, or a string representing the name of a method in this class.
	 *
	 * @param string          $hook_name       The name of the filter to add the callback to.
	 * @param callable|string $callback        The callback to be run when the filter is called.
	 * @param int             $priority        Optional. Used to specify the order in which the functions
	 *                                         associated with a particular filter are executed.
	 *                                         Lower numbers correspond with earlier execution,
	 *                                         and functions with the same priority are executed
	 *                                         in the order in which they were added to the filter. Default 10.
	 * @param int             $accepted_args   Optional. The number of arguments the function accepts. Default 1.
	 */
	protected static function add_filter( string $hook_name, $callback, int $priority = 10, int $accepted_args = 1 ): void {
		self::process_callback_before_hooking( $callback );
		add_filter( $hook_name, $callback, $priority, $accepted_args );
	}

	/**
	 * Do the required processing to a callback before invoking the WordPress 'add_action' or 'add_filter' function.
	 *
	 * @param callable $callback The callback to process.
	 * @return void
	 */
	protected static function process_callback_before_hooking( $callback ): void {
		if ( ! is_array( $callback ) || count( $callback ) &lt; 2 ) {
			return;
		}

		$first_item = $callback[0];
		if ( __CLASS__ === $first_item ) {
			static::mark_static_method_as_accessible( $callback[1] );
		} elseif ( is_object( $first_item ) &amp;&amp; get_class( $first_item ) === __CLASS__ ) {
			$first_item-&gt;mark_method_as_accessible( $callback[1] );
		}
	}

	/**
	 * Register a private or protected instance method of this class as externally accessible.
	 *
	 * @param string $method_name Method name.
	 * @return bool True if the method has been marked as externally accessible, false if the method doesn't exist.
	 */
	protected function mark_method_as_accessible( string $method_name ): bool {
		// Note that an &quot;is_callable&quot; check would be useless here:
		// &quot;is_callable&quot; always returns true if the class implements __call.
		if ( method_exists( $this, $method_name ) ) {
			$this-&gt;_accessible_private_methods[ $method_name ] = $method_name;
			return true;
		}

		return false;
	}

	/**
	 * Register a private or protected static method of this class as externally accessible.
	 *
	 * @param string $method_name Method name.
	 * @return bool True if the method has been marked as externally accessible, false if the method doesn't exist.
	 */
	protected static function mark_static_method_as_accessible( string $method_name ): bool {
		if ( method_exists( __CLASS__, $method_name ) ) {
			static::$_accessible_static_private_methods[ $method_name ] = $method_name;
			return true;
		}

		return false;
	}

	/**
	 * Undefined/inaccessible instance method call handler.
	 *
	 * @param string $name Called method name.
	 * @param array  $arguments Called method arguments.
	 * @return mixed
	 * @throws \Error The called instance method doesn't exist or is private/protected and not marked as externally accessible.
	 */
	public function __call( $name, $arguments ) {
		if ( isset( $this-&gt;_accessible_private_methods[ $name ] ) ) {
			return call_user_func_array( array( $this, $name ), $arguments );
		} elseif ( is_callable( array( 'parent', '__call' ) ) ) {
			return parent::__call( $name, $arguments );
		} elseif ( method_exists( $this, $name ) ) {
			throw new \Error( 'Call to private method ' . get_class( $this ) . '::' . $name );
		} else {
			throw new \Error( 'Call to undefined method ' . get_class( $this ) . '::' . $name );
		}
	}

	/**
	 * Undefined/inaccessible static method call handler.
	 *
	 * @param string $name Called method name.
	 * @param array  $arguments Called method arguments.
	 * @return mixed
	 * @throws \Error The called static method doesn't exist or is private/protected and not marked as externally accessible.
	 */
	public static function __callStatic( $name, $arguments ) {
		if ( isset( static::$_accessible_static_private_methods[ $name ] ) ) {
			return call_user_func_array( array( __CLASS__, $name ), $arguments );
		} elseif ( is_callable( array( 'parent', '__callStatic' ) ) ) {
			return parent::__callStatic( $name, $arguments );
		} elseif ( 'add_action' === $name || 'add_filter' === $name ) {
			$proper_method_name = 'add_static_' . substr( $name, 4 );
			throw new \Error( __CLASS__ . '::' . $name . &quot; can't be called statically, did you mean '$proper_method_name'?&quot; );
		} elseif ( method_exists( __CLASS__, $name ) ) {
			throw new \Error( 'Call to private method ' . __CLASS__ . '::' . $name );
		} else {
			throw new \Error( 'Call to undefined method ' . __CLASS__ . '::' . $name );
		}
	}
}
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