function add_used_css_to_html( string $html, string $used_css ): string {
		$replace = preg_replace(
			'#</title>#iU',
			'</title>' . $this->get_used_css_markup( $used_css ),
			$html,
			1
		);

		if ( null === $replace ) {
			return $html;
		}

		return $replace;
	}

	/**
	 * Return Markup for used_css into the page.
	 *
	 * @param string $used_css Used CSS content.
	 *
	 * @return string
	 */
	private function get_used_css_markup( string $used_css ): string {
		/**
		 * Filters Used CSS content before output.
		 *
		 * @since 3.9.0.2
		 *
		 * @param string $used_css Used CSS content.
		 */
		$used_css = apply_filters( 'rocket_usedcss_content', $used_css );

		$used_css = str_replace( '\\', '\\\\', $used_css );// Guard the backslashes before passing the content to preg_replace.
		$used_css = $this->handle_charsets( $used_css, false );

		return sprintf(
			'<style id="wpr-usedcss">%s</style>',
			$used_css
		);
	}

	/**
	 * Determines if the page is mobile and separate cache for mobile files is enabled.
	 *
	 * @return boolean
	 */
	private function is_mobile(): bool {
		return $this->options->get( 'cache_mobile', 0 )
			&& $this->options->get( 'do_caching_mobile_files', 0 )
			&& wp_is_mobile();
	}

	/**
	 * Check if current page is the home page.
	 *
	 * @param string $url Current page url.
	 *
	 * @return bool
	 */
	private function is_home( string $url ): bool {
		/**
		 * Filters the home url.
		 *
		 * @since 3.11.4
		 *
		 * @param string  $home_url home url.
		 * @param string  $url url of current page.
		 */
		$home_url = apply_filters( 'rocket_rucss_is_home_url', home_url(), $url );
		return untrailingslashit( $url ) === untrailingslashit( $home_url );
	}

	/**
	 * Process pending jobs inside cron iteration.
	 *
	 * @return void
	 */
	public function process_pending_jobs() {
		Logger::debug( 'RUCSS: Start processing pending jobs inside cron.' );

		if ( ! $this->is_enabled() ) {
			Logger::debug( 'RUCSS: Stop processing cron iteration because option is disabled.' );

			return;
		}

		// Get some items from the DB with status=pending & job_id isn't empty.

		/**
		 * Filters the pending jobs count.
		 *
		 * @since 3.11
		 *
		 * @param int $rows Number of rows to grab with each CRON iteration.
		 */
		$rows = apply_filters( 'rocket_rucss_pending_jobs_cron_rows_count', 100 );

		Logger::debug( "RUCSS: Start getting number of {$rows} pending jobs." );

		$pending_jobs = $this->used_css_query->get_pending_jobs( $rows );
		if ( ! $pending_jobs ) {
			Logger::debug( 'RUCSS: No pending jobs are there.' );

			return;
		}

		foreach ( $pending_jobs as $used_css_row ) {
			Logger::debug( "RUCSS: Send the job for url {$used_css_row->url} to Async task to check its job status." );

			// Change status to in-progress.
			$this->used_css_query->make_status_inprogress( (int) $used_css_row->id );

			$this->queue->add_job_status_check_async( (int) $used_css_row->id );
		}
	}

	/**
	 * Check job status by DB row ID.
	 *
	 * @param int $id DB Row ID.
	 *
	 * @return void
	 */
	public function check_job_status( int $id ) {
		Logger::debug( 'RUCSS: Start checking job status for row ID: ' . $id );
		$new_job_id  = false;
		$row_details = $this->used_css_query->get_item( $id );
		if ( ! $row_details ) {
			Logger::debug( 'RUCSS: Row ID not found ', compact( 'id' ) );

			// Nothing in DB, bailout.
			return;
		}

		// Send the request to get the job status from SaaS.
		$job_details = $this->api->get_queue_job_status( $row_details->job_id, $row_details->queue_name, $this->is_home( $row_details->url ) );

		/**
		 * Filters the rocket min rucss css result size.
		 *
		 * @since 3.13.3
		 *
		 * @param int min size.
		 */
		$min_rucss_size = apply_filters( 'rocket_min_rucss_size', 150 );
		if ( ! is_numeric( $min_rucss_size ) ) {
			$min_rucss_size = 150;
		}

		if ( isset( $job_details['contents']['shakedCSS_size'] ) && intval( $job_details['contents']['shakedCSS_size'] ) < $min_rucss_size ) {
			$message = 'RUCSS: shakedCSS size is less than ' . $min_rucss_size;
			Logger::error( $message );
			$this->used_css_query->make_status_failed( $id, '500', $message );
			return;
		}

		if (
			200 !== $job_details['code']
			||
			empty( $job_details['contents'] )
			||
			! isset( $job_details['contents']['shakedCSS'] )
		) {
			Logger::debug( 'RUCSS: Job status failed for url: ' . $row_details->url, $job_details );

			// Failure, check the retries number.
			if ( $row_details->retries >= 3 ) {
				Logger::debug( 'RUCSS: Job failed 3 times for url: ' . $row_details->url );
				/**
				 * Unlock preload URL.
				 *
				 * @param string $url URL to unlock
				 */
				do_action( 'rocket_preload_unlock_url', $row_details->url );

				$this->used_css_query->make_status_failed( $id, strval( $job_details['code'] ), $job_details['message'] );

				return;
			}

			// on timeout errors with code 408 create new job.
			switch ( $job_details['code'] ) {
				case 408:
					$add_to_queue_response = $this->add_url_to_the_queue( $row_details->url, (bool) $row_details->is_mobile );
					if ( false !== $add_to_queue_response ) {
						$new_job_id = $add_to_queue_response['contents']['jobId'];
						$this->used_css_query->update_job_id( $id, $new_job_id );
					}
					break;
			}

			// Increment the retries number with 1 , Change status to pending again and change job id on timeout.
			$this->used_css_query->increment_retries( $id, $row_details->retries );

			// @Todo: Maybe we can add this row to the async job to get the status before the next cron

			return;
		}
		/**
		 * Unlock preload URL.
		 *
		 * @param string $url URL to unlock
		 */
		do_action( 'rocket_preload_unlock_url', $row_details->url );

		$css = $this->apply_font_display_swap( $job_details['contents']['shakedCSS'] );

		$hash = md5( $css );

		if ( ! $this->filesystem->write_used_css( $hash, $css ) ) {
			$message = 'RUCSS: Could not write used CSS to the filesystem: ' . $row_details->url;
			Logger::error( $message );
			$this->used_css_query->make_status_failed( $id, '', $message );

			return;
		}

		// Everything is fine, save the usedcss into DB, change status to completed and reset queue_name and job_id.
		Logger::debug( 'RUCSS: Save used CSS for url: ' . $row_details->url );

		$this->used_css_query->make_status_completed( $id, $hash );

		/**
		 * Fires after successfully saving the used CSS for an URL
		 *
		 * @param string $url URL used to generated the used CSS.
		 * @param array  $job_details Result of the request to get the job status from SaaS.
		 */
		do_action( 'rocket_rucss_complete_job_status', $row_details->url, $job_details );
	}

	/**
	 * Add clear UsedCSS adminbar item.
	 *
	 * @param WP_Admin_Bar $wp_admin_bar Adminbar object.
	 *
	 * @return void
	 */
	public function add_clear_usedcss_bar_item( WP_Admin_Bar $wp_admin_bar ) {
		global $post;

		if ( 'local' === wp_get_environment_type() ) {
			return;
		}

		if ( ! current_user_can( 'rocket_remove_unused_css' ) ) {
			return;
		}

		if ( is_admin() ) {
			return;
		}

		if ( ! $this->can_optimize_url() ) {
			return;
		}

		if ( ! rocket_can_display_options() ) {
			return;
		}

		/**
		 * Filters the rocket `clear used css of this url` option on admin bar menu.
		 *
		 * @since 3.12.1
		 *
		 * @param bool  $should_skip Should skip adding `clear used css of this url` option in admin bar.
		 * @param type  $post Post object.
		 */
		if ( apply_filters( 'rocket_skip_admin_bar_clear_used_css_option', false, $post ) ) {
			return;
		}

		$referer = '';
		$action  = 'rocket_clear_usedcss_url';

		if ( ! empty( $_SERVER['REQUEST_URI'] ) ) {
			$referer_url = filter_var( wp_unslash( $_SERVER['REQUEST_URI'] ), FILTER_SANITIZE_URL );
			$referer     = '&_wp_http_referer=' . rawurlencode( remove_query_arg( 'fl_builder', $referer_url ) );
		}

		/**
		 * Clear usedCSS for this URL (frontend).
		 */
		$wp_admin_bar->add_menu(
			[
				'parent' => 'wp-rocket',
				'id'     => 'clear-usedcss-url',
				'title'  => __( 'Clear Used CSS of this URL', 'rocket' ),
				'href'   => wp_nonce_url( admin_url( 'admin-post.php?action=' . $action . $referer ), $action ),
			]
		);
	}

	/**
	 * Clear specific url.
	 *
	 * @param string $url Page url.
	 *
	 * @return void
	 */
	public function clear_url_usedcss( string $url ) {
		$this->delete_used_css( $url );

		/**
		 * Fires after clearing usedcss for specific url.
		 *
		 * @since 3.11
		 *
		 * @param string $url Current page URL.
		 */
		do_action( 'rocket_rucss_after_clearing_usedcss', $url );
	}

	/**
	 * Get the count of not completed rows.
	 *
	 * @return int
	 */
	public function get_not_completed_count() {
		return $this->used_css_query->get_not_completed_count();
	}

	/**
	 * Clear failed urls.
	 *
	 * @return void
	 */
	public function clear_failed_urls() {
		$rows = $this->used_css_query->get_failed_rows();

		if ( empty( $rows ) ) {
			return;
		}

		$failed_urls = [];

		foreach ( $rows as  $row ) {
			$failed_urls[] = $row->url;

			$id = (int) $row->id;

			if ( empty( $id ) ) {
				continue;
			}

			$this->used_css_query->revert_to_pending( $id );
		}

		/**
		 * Fires after clearing failed urls.
		 *
		 * @param array $urls Failed urls.
		 */
		do_action( 'rocket_rucss_after_clearing_failed_url', $failed_urls );
	}

	/**
	 * Add preload links for the fonts in the used CSS
	 *
	 * @param string $html HTML content.
	 * @param string $used_css Used CSS content.
	 *
	 * @return string
	 */
	private function add_used_fonts_preload( string $html, string $used_css ): string {
		/**
		 * Filters the fonts preload from the used CSS
		 *
		 * @since 3.11
		 *
		 * @param bool $enable True to enable, false to disable.
		 */
		if ( ! apply_filters( 'rocket_enable_rucss_fonts_preload', true ) ) {
			return $html;
		}

		if ( ! preg_match_all( '/@font-face\s*{\s*(?<content>[^}]+)}/is', $used_css, $font_faces, PREG_SET_ORDER ) ) {
			return $html;
		}

		if ( empty( $font_faces ) ) {
			return $html;
		}

		$urls = [];

		foreach ( $font_faces as $font_face ) {
			if ( empty( $font_face['content'] ) ) {
				continue;
			}

			$font_url = $this->extract_first_font( $font_face['content'] );

			/**
			 * Filters font URL with CDN hostname
			 *
			 * @since 3.11.4
			 *
			 * @param type  $url url to be rewritten.
			 */
			$font_url = apply_filters( 'rocket_font_url', $font_url );

			if ( empty( $font_url ) ) {
				continue;
			}

			$urls[] = $font_url;
		}

		if ( empty( $urls ) ) {
			return $html;
		}

		$urls = array_unique( $urls );

		$replace = preg_replace(
			'#</title>#iU',
			'</title>' . $this->preload_links( $urls ),
			$html,
			1
		);

		if ( null === $replace ) {
			return $html;
		}

		return $replace;
	}

	/**
	 * Remove preconnect tag for google api.
	 *
	 * @param string $html html content.
	 *
	 * @return string
	 */
	protected function remove_google_font_preconnect( string $html ): string {
		$clean_html = $this->hide_comments( $html );
		$clean_html = $this->hide_noscripts( $clean_html );
		$clean_html = $this->hide_scripts( $clean_html );
		$links      = $this->find(
			'<link\s+([^>]+[\s"\'])?rel\s*=\s*[\'"]((preconnect)|(dns-prefetch))[\'"]([^>]+)?\/?>',
			$clean_html,
			'Uis'
		);

		foreach ( $links as $link ) {
			if ( preg_match( '/href=[\'"](https:)?\/\/fonts.googleapis.com\/?[\'"]/', $link[0] ) ) {
				$html = str_replace( $link[0], '', $html );
			}
		}

		return $html;
	}

	/**
	 * Extracts the first font URL from the font-face declaration
	 *
	 * Skips .eot fonts if it exists
	 *
	 * @since 3.11
	 *
	 * @param string $font_face Font-face declaration content.
	 *
	 * @return string
	 */
	private function extract_first_font( string $font_face ): string {
		if ( ! preg_match_all( '/src:\s*(?<urls>[^;}]*)/is', $font_face, $sources, PREG_SET_ORDER ) ) {
			return '';
		}

		foreach ( $sources as $src ) {
			if ( empty( $src['urls'] ) ) {
				continue;
			}

			$urls = explode( ',', $src['urls'] );

			foreach ( $urls as $url ) {
				if ( false !== strpos( $url, '.eot' ) ) {
					continue;
				}

				if ( ! preg_match( '/url\(\s*[\'"]?(?<url>[^\'")]+)[\'"]?\)/is', $url, $matches ) ) {
					continue;
				}

				return trim( $matches['url'] );
			}
		}

		return '';
	}

	/**
	 * Converts an array of URLs to preload link tags
	 *
	 * @param array $urls An array of URLs.
	 *
	 * @return string
	 */
	private function preload_links( array $urls ): string {
		$links = '';

		foreach ( $urls as $url ) {
			$links .= '<link rel="preload" as="font" href="' . esc_url( $url ) . '" crossorigin>';
		}

		return $links;
	}

	/**
	 * Set Rucss inline attr exclusions
	 *
	 *  @return void
	 */
	private function set_inline_exclusions_lists() {
		$wpr_dynamic_lists               = $this->data_manager->get_lists();
		$this->inline_atts_exclusions    = isset( $wpr_dynamic_lists->rucss_inline_atts_exclusions ) ? $wpr_dynamic_lists->rucss_inline_atts_exclusions : [];
		$this->inline_content_exclusions = isset( $wpr_dynamic_lists->rucss_inline_content_exclusions ) ? $wpr_dynamic_lists->rucss_inline_content_exclusions : [];

	}

	/**
	 * Displays a notice if the used CSS folder is not writable
	 *
	 * @since 3.11.4
	 *
	 * @return void
	 */
	public function notice_write_permissions() {
		if ( ! current_user_can( 'rocket_manage_options' ) ) {
			return;
		}

		if ( ! $this->is_enabled() ) {
			return;
		}

		if ( $this->filesystem->is_writable_folder() ) {
			return;
		}

		$message = rocket_notice_writing_permissions( trim( str_replace( rocket_get_constant( 'ABSPATH', '' ), '', rocket_get_constant( 'WP_ROCKET_USED_CSS_PATH', '' ) ), '/' ) );

		rocket_notice_html(
			[
				'status'      => 'error',
				'dismissible' => '',
				'message'     => $message,
			]
		);
	}

	/**
	 * Validate the items in array to be strings only and preg_quote them.
	 *
	 * @param array $items Array to be validated and quoted.
	 *
	 * @return array|string[]
	 */
	private function validate_array_and_quote( array $items ) {
		$items_array = array_filter( $items, 'is_string' );

		return array_map(
			static function ( $item ) {
				return preg_quote( $item, '/' );
			},
			$items_array
		);
	}
}