_wp_link_page( int $i )

function _wp_link_page( $i ) {
	global $wp_rewrite;
	$post = get_post();
	$query_args = array();

	if ( 1 == $i ) {
		$url = get_permalink();
	} else {
		if ( '' == get_option('permalink_structure') || in_array($post->post_status, array('draft', 'pending')) )
			$url = add_query_arg( 'page', $i, get_permalink() );
		elseif ( 'page' == get_option('show_on_front') && get_option('page_on_front') == $post->ID )
			$url = trailingslashit(get_permalink()) . user_trailingslashit("$wp_rewrite->pagination_base/" . $i, 'single_paged');
		else
			$url = trailingslashit(get_permalink()) . user_trailingslashit($i, 'single_paged');
	}

	if ( is_preview() ) {

		if ( ( 'draft' !== $post->post_status ) && isset( $_GET['preview_id'], $_GET['preview_nonce'] ) ) {
			$query_args['preview_id'] = wp_unslash( $_GET['preview_id'] );
			$query_args['preview_nonce'] = wp_unslash( $_GET['preview_nonce'] );
		}

		$url = get_preview_post_link( $post, $query_args, $url );
	}

	return '<a href="' . esc_url( $url ) . '" class="post-page-numbers">';
}