Radio metabox

class page_metabox {

	public function __construct() {

		if ( is_admin() ) {
			add_action( 'load-post.php',     array( $this, 'init_metabox' ) );
			add_action( 'load-post-new.php', array( $this, 'init_metabox' ) );
		}

	}

	public function init_metabox() {

		add_action( 'add_meta_boxes', array( $this, 'add_metabox'  )        );
		add_action( 'save_post',      array( $this, 'save_metabox' ), 10, 2 );

	}

	public function add_metabox() {

		add_meta_box(
			'page_metaboxe',
			__( 'Advanced Options', 'moreshet-ladino' ),
			array( $this, 'render_metabox' ),
			'page',
			'side',
			'high'
		);

	}

	public function render_metabox( $post ) {

		// Retrieve an existing value from the database.
		$sg_sidebar_right_book = get_post_meta( $post->ID, 'sg_sidebar_right_book', true );

		// Set default values.
		if( empty( $sg_sidebar_right_book ) ) $sg_sidebar_right_book = '';

		// Form fields.
		echo '<table class="form-table">';

		echo '	<tr>';
		echo '		<th><label for="sg_sidebar_right_book" class="sg_sidebar_right_book_label">' . __( 'Style', 'moreshet-ladino' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="radio" name="sg_sidebar_right_book" class="sg_sidebar_right_book_field" value="sg_regular " ' . checked( $sg_sidebar_right_book, 'sg_regular ', false ) . '> ' . __( ' Regular', 'moreshet-ladino' ) . '<br>';
		echo '			<input type="radio" name="sg_sidebar_right_book" class="sg_sidebar_right_book_field" value="sg_sidebar_right_book " ' . checked( $sg_sidebar_right_book, 'sg_sidebar_right_book ', false ) . '> ' . __( ' Sidebar Right', 'moreshet-ladino' ) . '<br>';
		echo '		</td>';
		echo '	</tr>';

		echo '</table>';

	}

	public function save_metabox( $post_id, $post ) {

		// Check if it's not a revision.
		if ( wp_is_post_revision( $post_id ) )
			return;

		// Sanitize user input.
		$sg_new_sidebar_right_book = isset( $_POST[ 'sg_sidebar_right_book' ] ) ? $_POST[ 'sg_sidebar_right_book' ] : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'sg_sidebar_right_book', $sg_new_sidebar_right_book );

	}

}

new page_metabox;