s[ $src ] = $id;
		}

		return $images;
	}

	/**
	 * Extracts image ID out of the image's classes.
	 *
	 * @param string $classes The classes assigned to the image.
	 *
	 * @return int The ID that's extracted from the classes.
	 */
	protected function extract_id_of_classes( $classes ) {
		if ( ! $classes ) {
			return 0;
		}

		/**
		 * Filter 'wpseo_extract_id_pattern' - Allows filtering the regex patern to be used to extract image IDs from class/attribute names.
		 *
		 * Defaults to the pattern that extracts image IDs from core's `wp-image-<ID>` native format in image classes.
		 *
		 * @api string The regex pattern to be used to extract image IDs from class names. Empty string if the whole class/attribute should be returned.
		 */
		$pattern = \apply_filters( 'wpseo_extract_id_pattern', '/(?<!\S)wp-image-(\d+)(?!\S)/i' );

		if ( $pattern === '' ) {
			return (int) $classes;
		}

		$matches = [];

		if ( preg_match( $pattern, $classes, $matches ) ) {
			return (int) $matches[1];
		}

		return 0;
	}

	/**
	 * Gathers all images from content.
	 *
	 * @param string $content The content.
	 *
	 * @return int[] An associated array of image IDs, keyed by their URLs.
	 */
	protected function gather_images( $content ) {

		/**
		 * Filter 'wpseo_force_creating_and_using_attachment_indexables' - Filters if we should use attachment indexables to find all content images. Instead of scanning the content.
		 *
		 * The default value is false.
		 *
		 * @since 21.1
		 */
		$should_not_parse_content = \apply_filters( 'wpseo_force_creating_and_using_attachment_indexables', false );

		/**
		 * Filter 'wpseo_force_skip_image_content_parsing' - Filters if we should force skip scanning the content to parse images.
		 * This filter can be used if the regex gives a faster result than scanning the code.
		 *
		 * The default value is false.
		 *
		 * @since 21.1
		 */
		$should_not_parse_content = \apply_filters( 'wpseo_force_skip_image_content_parsing', $should_not_parse_content );
		if ( ! $should_not_parse_content && class_exists( WP_HTML_Tag_Processor::class ) ) {
			return $this->gather_images_wp( $content );
		}

		if ( ! $should_not_parse_content && class_exists( DOMDocument::class ) ) {
			return $this->gather_images_DOMDocument( $content );
		}

		if ( \strpos( $content, 'src' ) === false ) {
			// Nothing to do.
			return [];
		}

		$images = [];
		$regexp = '<img\s[^>]*src=("??)([^" >]*?)\\1[^>]*>';
		// Used modifiers iU to match case insensitive and make greedy quantifiers lazy.
		if ( \preg_match_all( "/$regexp/iU", $content, $matches, \PREG_SET_ORDER ) ) {
			foreach ( $matches as $match ) {
				$images[ $match[2] ] = 0;
			}
		}

		return $images;
	}

	/**
	 * Creates link models from lists of URLs and image sources.
	 *
	 * @param Indexable $indexable The indexable.
	 * @param string[]  $links     The link URLs.
	 * @param int[]     $images    The image sources.
	 *
	 * @return SEO_Links[] The link models.
	 */
	protected function create_links( $indexable, $links, $images ) {
		$home_url    = \wp_parse_url( \home_url() );
		$current_url = \wp_parse_url( $indexable->permalink );
		$links       = \array_map(
			function( $link ) use ( $home_url, $indexable ) {
				return $this->create_internal_link( $link, $home_url, $indexable );
			},
			$links
		);
		// Filter out links to the same page with a fragment or query.
		$links = \array_filter(
			$links,
			function ( $link ) use ( $current_url ) {
				return $this->filter_link( $link, $current_url );
			}
		);

		$image_links = [];
		foreach ( $images as $image_url => $image_id ) {
			$image_links[] = $this->create_internal_link( $image_url, $home_url, $indexable, true, $image_id );
		}

		return \array_merge( $links, $image_links );
	}

	/**
	 * Get the post ID based on the link's type and its target's permalink.
	 *
	 * @param string $type      The type of link (either SEO_Links::TYPE_INTERNAL or SEO_Links::TYPE_INTERNAL_IMAGE).
	 * @param string $permalink The permalink of the link's target.
	 *
	 * @return int The post ID.
	 */
	protected function get_post_id( $type, $permalink ) {
		if ( $type === SEO_Links::TYPE_INTERNAL ) {
			return \url_to_postid( $permalink );
		}

		return $this->image_helper->get_attachment_by_url( $permalink );
	}

	/**
	 * Creates an internal link.
	 *
	 * @param string    $url       The url of the link.
	 * @param array     $home_url  The home url, as parsed by wp_parse_url.
	 * @param Indexable $indexable The indexable of the post containing the link.
	 * @param bool      $is_image  Whether or not the link is an image.
	 * @param int       $image_id  The ID of the internal image.
	 *
	 * @return SEO_Links The created link.
	 */
	protected function create_internal_link( $url, $home_url, $indexable, $is_image = false, $image_id = 0 ) {
		$parsed_url = \wp_parse_url( $url );
		$link_type  = $this->url_helper->get_link_type( $parsed_url, $home_url, $is_image );

		/**
		 * ORM representing a link in the SEO Links table.
		 *
		 * @var SEO_Links $model
		 */
		$model = $this->seo_links_repository->query()->create(
			[
				'url'          => $url,
				'type'         => $link_type,
				'indexable_id' => $indexable->id,
				'post_id'      => $indexable->object_id,
			]
		);

		$model->parsed_url = $parsed_url;

		if ( $model->type === SEO_Links::TYPE_INTERNAL ) {
			$permalink = $this->build_permalink( $url, $home_url );

			return $this->enhance_link_from_indexable( $model, $permalink );
		}

		if ( $model->type === SEO_Links::TYPE_INTERNAL_IMAGE ) {
			$permalink = $this->build_permalink( $url, $home_url );

			/** The `wpseo_force_creating_and_using_attachment_indexables` filter is documented in indexable-link-builder.php */
			if ( ! $this->options_helper->get( 'disable-attachment' ) || \apply_filters( 'wpseo_force_creating_and_using_attachment_indexables', false ) ) {
				$model = $this->enhance_link_from_indexable( $model, $permalink );
			}
			else {
				$target_post_id = ( $image_id !== 0 ) ? $image_id : WPSEO_Image_Utils::get_attachment_by_url( $permalink );

				if ( ! empty( $target_post_id ) ) {
					$model->target_post_id = $target_post_id;
				}
			}

			if ( $model->target_post_id ) {
				$file = \get_attached_file( $model->target_post_id );

				if ( $file ) {
					if ( \file_exists( $file ) ) {
						$model->size = \filesize( $file );
					}
					else {
						$model->size = null;
					}

					list( , $width, $height ) = \wp_get_attachment_image_src( $model->target_post_id, 'full' );
					$model->width             = $width;
					$model->height            = $height;
				}
				else {
					$model->width  = 0;
					$model->height = 0;
					$model->size   = 0;
				}
			}
		}

		return $model;
	}

	/**
	 * Enhances the link model with information from its indexable.
	 *
	 * @param SEO_Links $model     The link's model.
	 * @param string    $permalink The link's permalink.
	 *
	 * @return SEO_Links The enhanced link model.
	 */
	protected function enhance_link_from_indexable( $model, $permalink ) {
		$target = $this->indexable_repository->find_by_permalink( $permalink );

		if ( ! $target ) {
			// If target indexable cannot be found, create one based on the post's post ID.
			$post_id = $this->get_post_id( $model->type, $permalink );
			if ( $post_id && $post_id !== 0 ) {
				$target = $this->indexable_repository->find_by_id_and_type( $post_id, 'post' );
			}
		}

		if ( ! $target ) {
			return $model;
		}

		$model->target_indexable_id = $target->id;
		if ( $target->object_type === 'post' ) {
			$model->target_post_id = $target->object_id;
		}

		if ( $model->target_indexable_id ) {
			$model->language = $target->language;
			$model->region   = $target->region;
		}

		return $model;
	}

	/**
	 * Builds the link's permalink.
	 *
	 * @param string $url      The url of the link.
	 * @param array  $home_url The home url, as parsed by wp_parse_url.
	 *
	 * @return string The link's permalink.
	 */
	protected function build_permalink( $url, $home_url ) {
		$permalink = $this->get_permalink( $url, $home_url );

		if ( $this->url_helper->is_relative( $permalink ) ) {
			// Make sure we're checking against the absolute URL, and add a trailing slash if the site has a trailing slash in its permalink settings.
			$permalink = $this->url_helper->ensure_absolute_url( \user_trailingslashit( $permalink ) );
		}

		return $permalink;
	}

	/**
	 * Filters out links that point to the same page with a fragment or query.
	 *
	 * @param SEO_Links $link        The link.
	 * @param array     $current_url The url of the page the link is on, as parsed by wp_parse_url.
	 *
	 * @return bool Whether or not the link should be filtered.
	 */
	protected function filter_link( SEO_Links $link, $current_url ) {
		$url = $link->parsed_url;

		// Always keep external links.
		if ( $link->type === SEO_Links::TYPE_EXTERNAL ) {
			return true;
		}

		// Always keep links with an empty path or pointing to other pages.
		if ( isset( $url['path'] ) ) {
			return empty( $url['path'] ) || $url['path'] !== $current_url['path'];
		}

		// Only keep links to the current page without a fragment or query.
		return ( ! isset( $url['fragment'] ) && ! isset( $url['query'] ) );
	}

	/**
	 * Updates the link counts for related indexables.
	 *
	 * @param Indexable   $indexable The indexable.
	 * @param SEO_Links[] $links     The link models.
	 *
	 * @return void
	 */
	protected function update_related_indexables( $indexable, $links ) {
		// Old links were only stored by post id, so remove all old seo links for this post that have no indexable id.
		// This can be removed if we ever fully clear all seo links.
		if ( $indexable->object_type === 'post' ) {
			$this->seo_links_repository->delete_all_by_post_id_where_indexable_id_null( $indexable->object_id );
		}

		$updated_indexable_ids = [];
		$old_links             = $this->seo_links_repository->find_all_by_indexable_id( $indexable->id );

		$links_to_remove = $this->links_diff( $old_links, $links );
		$links_to_add    = $this->links_diff( $links, $old_links );

		if ( ! empty( $links_to_remove ) ) {
			$this->seo_links_repository->delete_many_by_id( \wp_list_pluck( $links_to_remove, 'id' ) );
		}

		if ( ! empty( $links_to_add ) ) {
			$this->seo_links_repository->insert_many( $links_to_add );
		}

		foreach ( $links_to_add as $link ) {
			if ( $link->target_indexable_id ) {
				$updated_indexable_ids[] = $link->target_indexable_id;
			}
		}
		foreach ( $links_to_remove as $link ) {
			if ( $link->target_indexable_id ) {
				$updated_indexable_ids[] = $link->target_indexable_id;
			}
		}

		$this->update_incoming_links_for_related_indexables( $updated_indexable_ids );
	}

	/**
	 * Creates a diff between two arrays of SEO links, based on urls.
	 *
	 * @param SEO_Links[] $links_a The array to compare.
	 * @param SEO_Links[] $links_b The array to compare against.
	 *
	 * @return SEO_Links[] Links that are in $links_a, but not in $links_b.
	 */
	protected function links_diff( $links_a, $links_b ) {
		return \array_udiff(
			$links_a,
			$links_b,
			static function( SEO_Links $link_a, SEO_Links $link_b ) {
				return \strcmp( $link_a->url, $link_b->url );
			}
		);
	}

	/**
	 * Returns the number of internal links in an array of link models.
	 *
	 * @param SEO_Links[] $links The link models.
	 *
	 * @return int The number of internal links.
	 */
	protected function get_internal_link_count( $links ) {
		$internal_link_count = 0;

		foreach ( $links as $link ) {
			if ( $link->type === SEO_Links::TYPE_INTERNAL ) {
				++$internal_link_count;
			}
		}

		return $internal_link_count;
	}

	/**
	 * Returns a cleaned permalink for a given link.
	 *
	 * @param string $link     The raw URL.
	 * @param array  $home_url The home URL, as parsed by wp_parse_url.
	 *
	 * @return string The cleaned permalink.
	 */
	protected function get_permalink( $link, $home_url ) {
		// Get rid of the #anchor.
		$url_split = \explode( '#', $link );
		$link      = $url_split[0];

		// Get rid of URL ?query=string.
		$url_split = \explode( '?', $link );
		$link      = $url_split[0];

		// Set the correct URL scheme.
		$link = \set_url_scheme( $link, $home_url['scheme'] );

		// Add 'www.' if it is absent and should be there.
		if ( \strpos( $home_url['host'], 'www.' ) === 0 && \strpos( $link, '://www.' ) === false ) {
			$link = \str_replace( '://', '://www.', $link );
		}

		// Strip 'www.' if it is present and shouldn't be.
		if ( \strpos( $home_url['host'], 'www.' ) !== 0 ) {
			$link = \str_replace( '://www.', '://', $link );
		}

		return $link;
	}

	/**
	 * Updates incoming link counts for related indexables.
	 *
	 * @param int[] $related_indexable_ids The IDs of all related indexables.
	 *
	 * @return void
	 */
	protected function update_incoming_links_for_related_indexables( $related_indexable_ids ) {
		if ( empty( $related_indexable_ids ) ) {
			return;
		}

		$counts = $this->seo_links_repository->get_incoming_link_counts_for_indexable_ids( $related_indexable_ids );
		foreach ( $counts as $count ) {

			$this->indexable_repository->update_incoming_link_count( $count['target_indexable_id'], $count['incoming'] );
		}
	}
}