add new template tag: get attachment ID from it's URL

inc/template-tags.php

@@ -216,3 +216,40 @@ function _s_get_post_image_uri( $size = 'thumbnail' ) {
 
 	return $media_url;
 }
+
+/**
+ * Get an attachment ID from it's URL.
+ *
+ * @param  string  $attachment_url  The URL of the attachment.
+ * @return int                      The attachment ID.
+ */
+function _s_get_attachment_id_from_url( $attachment_url = '' ) {
+
+	global $wpdb;
+
+	$attachment_id = false;
+
+	// If there is no url, return.
+	if ( '' == $attachment_url ) {
+		return;
+	}
+
+	// Get the upload directory paths
+	$upload_dir_paths = wp_upload_dir();
+
+	// Make sure the upload path base directory exists in the attachment URL, to verify that we're working with a media library image
+	if ( false !== strpos( $attachment_url, $upload_dir_paths['baseurl'] ) ) {
+
+		// If this is the URL of an auto-generated thumbnail, get the URL of the original image
+		$attachment_url = preg_replace( '/-\d+x\d+(?=\.(jpg|jpeg|png|gif)$)/i', '', $attachment_url );
+
+		// Remove the upload path base directory from the attachment URL
+		$attachment_url = str_replace( $upload_dir_paths['baseurl'] . '/', '', $attachment_url );
+
+		// Finally, run a custom database query to get the attachment ID from the modified attachment URL
+		$attachment_id = $wpdb->get_var( $wpdb->prepare( "SELECT wposts.ID FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta WHERE wposts.ID = wpostmeta.post_id AND wpostmeta.meta_key = '_wp_attached_file' AND wpostmeta.meta_value = '%s' AND wposts.post_type = 'attachment'", $attachment_url ) );
+
+	}
+
+	return $attachment_id;
+}