WordPress Versions Metabox

WordPress versions data from https://codex.wordpress.org/WordPress_Versions

class Version_Info_Meta_Box {

	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(
			'version_info',
			__( 'Version Info', 'wpinfo' ),
			array( $this, 'render_metabox' ),
			'version',
			'advanced',
			'default'
		);

	}

	public function render_metabox( $post ) {

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

		// Retrieve an existing value from the database.
		$name = get_post_meta( $post->ID, 'name', true );
		$musican = get_post_meta( $post->ID, 'musican', true );
		$release = get_post_meta( $post->ID, 'release', true );
		$blog = get_post_meta( $post->ID, 'blog', true );
		$db_version = get_post_meta( $post->ID, 'db_version', true );

		// Set default values.
		if( empty( $name ) ) $name = '';
		if( empty( $musican ) ) $musican = '';
		if( empty( $release ) ) $release = '';
		if( empty( $blog ) ) $blog = '';
		if( empty( $db_version ) ) $db_version = '';

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

		echo '	<tr>';
		echo '		<th><label for="name" class="name_label">' . __( 'Name', 'wpinfo' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="text" id="name" name="name" class="name_field" placeholder="' . esc_attr__( '', 'wpinfo' ) . '" value="' . esc_attr__( $name ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="musican" class="musican_label">' . __( 'Musican', 'wpinfo' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="text" id="musican" name="musican" class="musican_field" placeholder="' . esc_attr__( '', 'wpinfo' ) . '" value="' . esc_attr__( $musican ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="release" class="release_label">' . __( 'Release Date', 'wpinfo' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="text" id="release" name="release" class="release_field" placeholder="' . esc_attr__( 'yyyy-mm-dd hh:mm:ss', 'wpinfo' ) . '" value="' . esc_attr__( $release ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="blog" class="blog_label">' . __( 'Blog', 'wpinfo' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="blog" name="blog" class="blog_field" placeholder="' . esc_attr__( 'https://', 'wpinfo' ) . '" value="' . esc_attr__( $blog ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="db_version" class="db_version_label">' . __( 'Datebase Version', 'wpinfo' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="number" id="db_version" name="db_version" class="db_version_field" placeholder="' . esc_attr__( '', 'wpinfo' ) . '" value="' . esc_attr__( $db_version ) . '">';
		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;

		// Check if it's not an autosave.
		if ( wp_is_post_autosave( $post_id ) )
			return;

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

		// Sanitize user input.
		$new_name = isset( $_POST[ 'name' ] ) ? sanitize_text_field( $_POST[ 'name' ] ) : '';
		$new_musican = isset( $_POST[ 'musican' ] ) ? sanitize_text_field( $_POST[ 'musican' ] ) : '';
		$new_release = isset( $_POST[ 'release' ] ) ? sanitize_text_field( $_POST[ 'release' ] ) : '';
		$new_blog = isset( $_POST[ 'blog' ] ) ? esc_url( $_POST[ 'blog' ] ) : '';
		$new_db_version = isset( $_POST[ 'db_version' ] ) ? floatval( $_POST[ 'db_version' ] ) : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'name', $new_name );
		update_post_meta( $post_id, 'musican', $new_musican );
		update_post_meta( $post_id, 'release', $new_release );
		update_post_meta( $post_id, 'blog', $new_blog );
		update_post_meta( $post_id, 'db_version', $new_db_version );

	}

}

new Version_Info_Meta_Box;