Introduce DuplicatePostFilter #49

inc/Import/Filter/DuplicatePostFilter.php

@@ -0,0 +1,79 @@
+<?php # -*- coding: utf-8 -*-
+
+namespace W2M\Import\Filter;
+
+use
+	W2M\Import\Common,
+	W2M\Import\Data,
+	W2M\Import\Type,
+	WP_Post;
+
+/**
+ * Class DuplicatePostFilter
+ *
+ * Todo: Write tests for
+ *
+ * @package W2M\Import\Filter
+ */
+class DuplicatePostFilter implements PostFilterInterface, Data\PostImportListenerInterface {
+
+	/**
+	 * @var string
+	 */
+	private $meta_key = '_w2m_remote_guid';
+
+	/**
+	 * @var Common\WpFactoryInterface
+	 */
+	private $wp_factory;
+
+	/**
+	 * @param Common\WpFactoryInterface $wp_factory (Optional)
+	 */
+	public function __construct( Common\WpFactoryInterface $wp_factory = NULL ) {
+
+		$this->wp_factory = $wp_factory
+			? $wp_factory
+			: new Common\WpFactory;
+	}
+
+	/**
+	 * Checks if a post should be imported or not
+	 *
+	 * @param Type\ImportPostInterface $import_post
+	 *
+	 * @return bool
+	 */
+	public function post_to_import( Type\ImportPostInterface $import_post ) {
+
+		$query = $this->wp_factory->wp_query(
+			[
+				'posts_per_page'         => 1,
+				'post_status'            => 'any',
+				'post_type'              => 'any',
+				'meta_key'               => $this->meta_key,
+				'meta_value'             => $import_post->guid(),
+				'fields'                 => 'ids',
+				'update_post_meta_cache' => FALSE,
+				'update_post_term_cache' => FALSE
+			]
+		);
+
+		return ! $query->have_posts();
+	}
+
+	/**
+	 * @wp-hook w2m_post_imported
+	 *
+	 * @param WP_Post $wp_post
+	 * @param Type\ImportPostInterface $import_post
+	 */
+	public function record_post( WP_Post $wp_post, Type\ImportPostInterface $import_post ) {
+
+		update_post_meta(
+			$wp_post->ID,
+			$this->meta_key,
+			$import_post->guid()
+		);
+	}
+}