WooCommerce: display more recent version of a product notice

more-recent-product.php

<?php

// Display Fields
add_action( 'woocommerce_product_options_related', 'woo_add_custom_fields' );

// Save Fields
add_action( 'woocommerce_process_product_meta', 'woo_add_custom_fields_save' );

// Display notice on proeuct page
add_action( 'woocommerce_single_product_summary', 'woo_display_more_recent_product_notice', 10 );

function woo_add_custom_fields() {

  global $woocommerce, $post;
  
  echo '<div class="options_group">';
  
  	?>
	<p class="form-field">
		<label for="more_recent_product_ids"><?php _e( 'More recent product', 'woocommerce' ); ?></label>
		<input type="hidden" class="wc-product-search" style="width: 50%;" id="more_recent_product_ids" name="more_recent_product_ids" data-placeholder="<?php esc_attr_e( 'Search for a product&hellip;', 'woocommerce' ); ?>" data-action="woocommerce_json_search_products" data-multiple="true" data-exclude="<?php echo intval( $post->ID ); ?>" data-selected="<?php
			$product_ids = array_filter( array_map( 'absint', (array) get_post_meta( $post->ID, '_more_recent_product_ids', true ) ) );
			$json_ids    = array();
			foreach ( $product_ids as $product_id ) {
				$product = wc_get_product( $product_id );
				if ( is_object( $product ) ) {
					$json_ids[ $product_id ] = wp_kses_post( html_entity_decode( $product->get_formatted_name(), ENT_QUOTES, get_bloginfo( 'charset' ) ) );
				}
			}
			echo esc_attr( json_encode( $json_ids ) );
		?>" value="<?php echo implode( ',', array_keys( $json_ids ) ); ?>" /> <?php echo wc_help_tip( __( 'Choose a more recent version of that product.', 'woocommerce' ) ); ?>
	</p>
	
	  
	<?php  echo '</div>';
	
}

function woo_add_custom_fields_save( $post_id ){
	
	$more_recent_product_ids = isset( $_POST['more_recent_product_ids'] ) ? array_filter( array_map( 'intval', explode( ',', $_POST['more_recent_product_ids'] ) ) ) : array();

	update_post_meta( $post_id, '_more_recent_product_ids', $more_recent_product_ids );
	
}

function woo_display_more_recent_product_notice() {

	global $post;
	
	$more_recent_product_ids = get_post_meta( $post->ID, '_more_recent_product_ids', true );
	
	if( $more_recent_product_ids != '' ) {
		
		$notice = '<p class="woocommerce_more_recent_product woocommerce-message">' . sprintf( wp_kses( __( 'There is a <a href="%s">newer version</a> of this product.', 'woocommerce' ), array(  'a' => array( 'href' => array() ) ) ), esc_url( get_permalink( $more_recent_product_ids[ 0 ]  ) ) ) . '</p>';
		
		echo $notice;

	}
	
}