Load globally used fonts and regenerate cache after changes

lib/compat/wordpress-6.0/class-wp-webfonts.php

@@ -37,6 +37,15 @@ class WP_Webfonts {
 	 */
 	private static $webfont_cache_option = 'gutenberg_used_webfonts';
 
+	/**
+	 * The name of the globally used webfont cache option name.
+	 *
+	 * @static
+	 * @access private
+	 * @var string
+	 */
+	private static $global_webfont_cache_option = 'gutenberg_globally_used_webfonts';
+
 	/**
 	 * An array of registered providers.
 	 *
@@ -71,19 +80,47 @@ public function init() {
 		}
 
 		add_action( 'init', array( $this, 'register_current_template_filter' ) );
+		add_action( 'init', array( $this, 'get_globally_used_fonts' ) );
 
 		add_action( 'switch_theme', array( $this, 'invalidate_used_webfonts_cache' ) );
 		add_action( 'save_post_wp_template', array( $this, 'invalidate_used_webfonts_cache' ) );
 		add_action( 'save_post_wp_template_part', array( $this, 'invalidate_used_webfonts_cache' ) );
 
 		add_filter( 'the_content', array( $this, 'register_webfonts_used_in_content' ) );
 
+		add_filter( 'rest_request_after_callbacks', array( $this, 'invalidate_globally_used_webfonts_cache' ), 10, 3 );
+
 		add_action( $hook, array( $this, 'generate_and_enqueue_styles' ) );
 
 		// Enqueue webfonts in the block editor.
 		add_action( 'admin_init', array( $this, 'generate_and_enqueue_editor_styles' ) );
 	}
 
+	public function invalidate_globally_used_webfonts_cache( $response, $handler, $request ) {
+		// TODO: identify Global Styles request and invalidate the global fonts cache.
+		// Or, maybe, build the cache here... Who knows.
+		return $response;
+	}
+
+	public function get_globally_used_fonts() {
+		$globally_used_webfonts = get_option( self::$global_webfont_cache_option );
+
+		if ( $globally_used_webfonts ) {
+			self::$used_webfonts = array_merge( self::$used_webfonts, $globally_used_webfonts );
+			return;
+		}
+
+		$globally_used_webfonts = $this->get_globally_used_webfonts();
+		update_option( self::$global_webfont_cache_option, $globally_used_webfonts );
+
+		self::$used_webfonts = array_merge( self::$used_webfonts, $globally_used_webfonts );
+	}
+
+	/**
+	 * Hook into every possible template so we can get the full template object on page load.
+	 *
+	 * @return void
+	 */
 	public function register_current_template_filter() {
 		$templates = get_block_templates( array(), 'wp_template' );
 
@@ -97,19 +134,29 @@ function() use ( $template ) {
 		}
 	}
 
+	/**
+	 * Look up used webfonts cache for the template that triggered the hook
+	 * registered on `register_current_template_filter`.
+	 *
+	 * If the webfonts array is not found there, parse the template, extract the webfonts
+	 * and register it in the option.
+	 *
+	 * @param WP_Template $template The template that is about to be rendered.
+	 * @return void
+	 */
 	public function register_used_webfonts_by_template( $template ) {
 		$used_webfonts_cache = get_option( self::$webfont_cache_option, array() );
 
 		if ( isset( $used_webfonts_cache[ $template->slug ] ) ) {
-			self::$used_webfonts = $used_webfonts_cache[ $template->slug ];
+			self::$used_webfonts = array_merge( self::$used_webfonts, $used_webfonts_cache[ $template->slug ] );
 			return;
 		}
 
 		$used_webfonts                          = $this->get_fonts_from_template( $template->content );
 		$used_webfonts_cache[ $template->slug ] = $used_webfonts;
 
 		update_option( self::$webfont_cache_option, $used_webfonts_cache );
-		self::$used_webfonts = $used_webfonts_cache[ $template->slug ];
+		self::$used_webfonts = array_merge( self::$used_webfonts, $used_webfonts_cache[ $template->slug ] );
 	}
 
 	/**
@@ -149,28 +196,6 @@ private function get_fonts_from_content( $content ) {
 		return $used_webfonts;
 	}
 
-	/**
-	 * Set list of used fonts in the current page.
-	 *
-	 * @return void
-	 */
-	public function load_used_webfonts() {
-		self::$used_webfonts = $this->get_globally_used_webfonts();
-		$used_webfonts       = get_option( self::$webfont_cache_option, array() );
-
-		foreach ( $used_webfonts as $template => $webfonts ) {
-			add_filter(
-				$template . '_template',
-				function() use ( $webfonts ) {
-					self::$used_webfonts = array_merge(
-						self::$used_webfonts,
-						$webfonts
-					);
-				}
-			);
-		}
-	}
-
 	/**
 	 * Get globally used webfonts.
 	 *