Headings meta bxes

class Offer_Headings {

	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(
			'headings',
			__( 'Overskrifter', 'Offer' ),
			array( $this, 'headings_callback' ),
			'page',
			'normal',
			'low'
		);

	}

	public function headings_callback( $post ) {

		// Add nonce for security and authentication.
		wp_nonce_field( 'nonce_action', 'nonce' );

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

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

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

		echo '	<tr>';
		echo '		<th><label for="heading" class="heading_label">' . __( 'Overskrift', 'Offer' ) . '</label></th>';
		echo '		<td>';
		echo '			<textarea id="heading" name="heading" class="heading_field" placeholder="' . esc_attr__( '', 'Offer' ) . '">' . $heading . '</textarea>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="subheading" class="subheading_label">' . __( 'Underoverskrift', 'Offer' ) . '</label></th>';
		echo '		<td>';
		echo '			<textarea id="subheading" name="subheading" class="subheading_field" placeholder="' . esc_attr__( '', 'Offer' ) . '">' . $subheading . '</textarea>';
		echo '		</td>';
		echo '	</tr>';

		echo '</table>';

	}

	public function save_metabox( $post_id, $post ) {

		// Add nonce for security and authentication.
		$nonce_name   = isset( $_POST['nonce'] ) ? $_POST['nonce'] : '';
		$nonce_action = 'nonce_action';

		// Check if a nonce is set.
		if ( ! isset( $nonce_name ) )
			return;

		// Check if a nonce is valid.
		if ( ! wp_verify_nonce( $nonce_name, $nonce_action ) )
			return;

		// Check if the user has permissions to save data.
		if ( ! current_user_can( 'edit_post', $post_id ) )
			return;

		// Sanitize user input.
		$new_heading = isset( $_POST[ 'heading' ] ) ? sanitize_text_field( $_POST[ 'heading' ] ) : '';
		$new_subheading = isset( $_POST[ 'subheading' ] ) ? sanitize_text_field( $_POST[ 'subheading' ] ) : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'heading', $new_heading );
		update_post_meta( $post_id, 'subheading', $new_subheading );

	}

}

new Offer_Headings;