Introduce interfaces for (meta) value filters #56

inc/Import/Filter/ValueFilterInterface.php

@@ -0,0 +1,21 @@
+<?php # -*- coding: utf-8 -*-
+
+namespace W2M\Import\Filter;
+
+/**
+ * Interface ValueFilterInterface
+ *
+ * Describes a unified filter for (meta) data
+ *
+ * @package W2M\Import\Filter
+ */
+interface ValueFilterInterface {
+
+	/**
+	 * @param mixed $value
+	 * @param int $object_id
+	 *
+	 * @return mixed (Same type as $value)
+	 */
+	public function filter( $value, $object_id );
+}

inc/Import/Filter/ValueFilterableInterface.php

@@ -0,0 +1,27 @@
+<?php # -*- coding: utf-8 -*-
+
+namespace W2M\Import\Filter;
+
+/**
+ * Interface ValueFilterableInterface
+ *
+ * During the process of (XML pull) import it is not stated that
+ * referenced instances already exists. With this interface, implementors
+ * have the ability to report this situation to get queued to the
+ * end of the process.
+ *
+ * @package W2M\Import\Filter
+ */
+interface ValueFilterableInterface extends ValueFilterInterface {
+
+	/**
+	 * Return FALSE when the filter is not filterable due to missing data. E.g. a post
+	 * ID refers to a post which was not imported yet.
+	 *
+	 * @param mixed $value
+	 * @param int $object_id
+	 *
+	 * @return bool
+	 */
+	public function is_filterable( $value, $object_id );
+}