CMC | Quickborn | Issue articles page numebrs

class add_issue_article_page_number_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(
			'page_number',
			__( 'Page number', 'issue-article' ),
			array( $this, 'render_metabox' ),
			'issue_article',
			'normal',
			'default'
		);

	}

	public function render_metabox( $post ) {

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

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

		// Set default values.
		if( empty( $cmc_quickborn_page_number_begin ) ) $cmc_quickborn_page_number_begin = '';
		if( empty( $cmc_quickborn_page_number_end ) ) $cmc_quickborn_page_number_end = '';
		if( empty( $cmc_quickborn_page_number_multipage ) ) $cmc_quickborn_page_number_multipage = '';

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

		echo '	<tr>';
		echo '		<th><label for="cmc_quickborn_page_number_begin" class="cmc_quickborn_page_number_begin_label">' . __( 'Begin (Must have)', 'issue-article' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="number" id="cmc_quickborn_page_number_begin" name="cmc_quickborn_page_number_begin" class="cmc_quickborn_page_number_begin_field" placeholder="' . esc_attr__( '', 'issue-article' ) . '" value="' . esc_attr__( $cmc_quickborn_page_number_begin ) . '">';
		echo '			<p class="description">' . __( 'Page number where article starts', 'issue-article' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="cmc_quickborn_page_number_end" class="cmc_quickborn_page_number_end_label">' . __( 'End', 'issue-article' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="number" id="cmc_quickborn_page_number_end" name="cmc_quickborn_page_number_end" class="cmc_quickborn_page_number_end_field" placeholder="' . esc_attr__( 'leave empty if single page', 'issue-article' ) . '" value="' . esc_attr__( $cmc_quickborn_page_number_end ) . '">';
		echo '			<p class="description">' . __( 'Leave empty if single page article.', 'issue-article' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="cmc_quickborn_page_number_multipage" class="cmc_quickborn_page_number_multipage_label">' . __( 'Multipage', 'issue-article' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="text" id="cmc_quickborn_page_number_multipage" name="cmc_quickborn_page_number_multipage" class="cmc_quickborn_page_number_multipage_field" placeholder="' . esc_attr__( '', 'issue-article' ) . '" value="' . esc_attr__( $cmc_quickborn_page_number_multipage ) . '">';
		echo '			<p class="description">' . __( 'If the item is not contiguous', 'issue-article' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '</table>';

	}

	public function save_metabox( $post_id, $post ) {

		// Add nonce for security and authentication.
		$nonce_name   = isset( $_POST['cmc_quickborn_nonce'] ) ? $_POST['cmc_quickborn_nonce'] : '';
		$nonce_action = 'cmc_quickborn_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.
		$cmc_quickborn_new_page_number_begin = isset( $_POST[ 'cmc_quickborn_page_number_begin' ] ) ? floatval( $_POST[ 'cmc_quickborn_page_number_begin' ] ) : '';
		$cmc_quickborn_new_page_number_end = isset( $_POST[ 'cmc_quickborn_page_number_end' ] ) ? floatval( $_POST[ 'cmc_quickborn_page_number_end' ] ) : '';
		$cmc_quickborn_new_page_number_multipage = isset( $_POST[ 'cmc_quickborn_page_number_multipage' ] ) ? sanitize_text_field( $_POST[ 'cmc_quickborn_page_number_multipage' ] ) : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'cmc_quickborn_page_number_begin', $cmc_quickborn_new_page_number_begin );
		update_post_meta( $post_id, 'cmc_quickborn_page_number_end', $cmc_quickborn_new_page_number_end );
		update_post_meta( $post_id, 'cmc_quickborn_page_number_multipage', $cmc_quickborn_new_page_number_multipage );

	}

}

new add_issue_article_page_number_meta_box;