Responsive Lightbox & Gallery Shortcode

function gallery_shortcode( $args ) {
		// enable only for frontend previews
		if ( ! is_admin() && is_preview() )
			add_filter( 'get_post_metadata', array( $this, 'filter_preview_metadata' ), 10, 4 );

		// prepare defaults
		$defaults = [ 'id' => 0 ];

		// merge defaults with arguments
		$args = array_merge( $defaults, $args );

		// parse id
		$args['id'] = (int) $args['id'];

		// is it gallery?
		if ( get_post_type( $args['id'] ) !== 'rl_gallery' )
			return '';

		$images_args = [ 'exclude' => true ];

		if ( isset( $args['preview'] ) )
			$images_args['preview'] = (bool) $args['preview'];
		elseif( isset( $_GET['rl_gallery_revision_id'], $_GET['preview'] ) && $_GET['preview'] === 'true' )
			$images_args['preview'] = true;
		else
			$images_args['preview'] = false;

		// get images
		$images = $this->get_gallery_images( $args['id'], $images_args );

		if ( ! $images )
			return '';

		$attachments = [];

		// build config
		foreach ( $images as $image ) {
			if ( ! empty( $image['id'] ) )
				$attachments[] = $image['id'];
		}

		// get config data
		$config = get_post_meta( $args['id'], '_rl_config', true );

		// prepare gallery shortcode parameters
		$fields = [];

		// get main instance
		$rl = Responsive_Lightbox();

		// valid menu item?
		if ( ! empty( $config['menu_item'] ) ) {
			// assign data from db
			$data = $config[$config['menu_item']];

			foreach ( $rl->frontend->get_default_gallery_fields() as $field_name => $field_args ) {
				// replace default values
				if ( array_key_exists( $field_name, $data ) )
					$fields[$field_name] = $data[$field_name];
			}

			// is it default gallery type?
			if ( $config['menu_item'] === 'default' ) {
				// set new gallery type
				$gallery_type = $rl->options['settings']['builder_gallery'];

				// assign gallery settings
				if ( array_key_exists( $gallery_type . '_gallery', $rl->settings->settings ) )
					$gallery_fields = $rl->settings->settings[$gallery_type . '_gallery']['fields'];

				// assign gallery defaults
				if ( array_key_exists( $gallery_type . '_gallery', $rl->options ) )
					$gallery_defaults = $rl->options[$gallery_type . '_gallery'];
			} else {
				$gallery_type = $config['menu_item'];

				// assign gallery settings
				if ( array_key_exists( $config['menu_item'] . '_gallery', $rl->settings->settings ) )
					$gallery_fields = $rl->settings->settings[$config['menu_item'] . '_gallery']['fields'];

				// assign gallery defaults
				if ( array_key_exists( $config['menu_item'] . '_gallery', $rl->defaults ) )
					$gallery_defaults = $rl->defaults[$config['menu_item'] . '_gallery'];
			}

			if ( isset( $gallery_fields, $gallery_defaults ) ) {
				// run through all fields
				foreach ( $gallery_fields as $field_name => $field_args ) {
					if ( $field_args['type'] === 'multiple' ) {
						foreach ( $field_args['fields'] as $subfield_name => $subfield_args ) {
							// field exists in db?
							if ( array_key_exists( $subfield_name, $data ) )
								$fields[$subfield_name] = $data[$subfield_name];
							else
								$fields[$subfield_name] = $gallery_defaults[$subfield_name];
						}
					} else {
						// field exists in db?
						if ( array_key_exists( $field_name, $data ) )
							$fields[$field_name] = $data[$field_name];
						else
							$fields[$field_name] = $gallery_defaults[$field_name];
					}
				}
			}
			// add gallery type
			$fields['type'] = $gallery_type;
		}

		$shortcode = '';

		foreach ( $fields as $arg => $value ) {
			if ( is_array( $value ) )
				$shortcode .= ' ' . esc_attr( $arg ) . '="' . esc_attr( (string) implode( ',', $value ) ) . '"';
			else
				$shortcode .= ' ' . esc_attr( $arg ) . '="' . esc_attr( (string) $value ) . '"';
		}

		// get design data
		$design = get_post_meta( $args['id'], '_rl_design', true );

		if ( ! empty( $design['menu_item'] ) ) {
			$design_data = $design[$design['menu_item']];

			// remove show_title to avoid shortcode attribute duplication
			if ( isset( $design_data['show_title'] ) ) {
				if ( ! isset( $design_data['design_show_title'] ) )
					$design_data['design_show_title'] = $design_data['show_title'];

				unset( $design_data['show_title'] );
			}

			// remove show_caption to avoid shortcode attribute duplication
			if ( isset( $design_data['show_caption'] ) ) {
				if ( ! isset( $design_data['design_show_caption'] ) )
					$design_data['design_show_caption'] = $design_data['show_caption'];

				unset( $design_data['show_caption'] );
			}

			foreach ( $design_data as $arg => $value ) {
				$shortcode .= ' ' . esc_attr( $arg ) . '="' . esc_attr( (string) $value ) . '"';
			}
		}

		// get lightbox data
		$lightbox = get_post_meta( $args['id'], '_rl_lightbox', true );

		if ( ! empty( $lightbox['menu_item'] ) ) {
			foreach ( $lightbox[$lightbox['menu_item']] as $arg => $value ) {
				$shortcode .= ' ' . esc_attr( $arg ) . '="' . esc_attr( (string) $value ) . '"';
			}
		}

		$forced_gallery_no = 0;

		// check forced gallery number
		if ( isset( $args['gallery_no'] ) ) {
			$args['gallery_no'] = (int) $args['gallery_no'];

			if ( $args['gallery_no'] > 0 )
				$forced_gallery_no = $args['gallery_no'];
		}

		// get content
		$content = do_shortcode( '[gallery rl_gallery_id="' . esc_attr( $args['id'] ) .'"' . ( $forced_gallery_no > 0 ? ' rl_gallery_no="' . (int) $forced_gallery_no .'"' : '' ) . ' include="' . ( empty( $attachments ) ? '' : esc_attr( implode( ',', $attachments ) ) ) . '"' . $shortcode . ']' );

		// make sure every filter is available in frontend ajax
		if ( wp_doing_ajax() )
			$content = $rl->frontend->add_lightbox( $content );

		return $content;
	}