Algol Plus Ltd

remove_filter('wapl_product_label', 'wapl_smart_product_label_filter');
add_filter('wapl_product_label', function($label) {

  global $product;

  // This in here for the admin preview to select one random product
  if ( ! $product ) {
    $product_posts = get_posts( array( 'post_type' => 'product', 'posts_per_page' => 1 ) );
    $product       = reset( $product_posts );
  }

  $product            = wc_get_product( $product );
  $highest_percentage = 0;

  if ( ! $product ) { // Check to be sure the global $product is set properly
    trigger_error( 'The global $product is not a valid variable type: ' . gettype( $product ) );
    return $label;
  }

  if ( $product->is_type( 'composite' ) ) {

    $regular_price      = $product->get_composite_regular_price();
    $sale_price         = $product->get_composite_price();
    $highest_percentage = ( $sale_price !== '' && $regular_price != 0 ) ? ( ( $regular_price - $sale_price ) / $regular_price * 100 ) : $highest_percentage;

  } elseif ( ! $product->is_type( 'variable' ) ) {

    $regular_price      = $product->get_regular_price();
    $sale_price         = $product->get_sale_price();
    $highest_percentage = ( $sale_price !== '' && $regular_price != 0 ) ? ( ( $regular_price - $sale_price ) / $regular_price * 100 ) : $highest_percentage;

  } else { // Get the right variable percentage

    foreach ( $product->get_children() as $child_id ) {
      $child = wc_get_product($child_id);

      $price = $child->get_regular_price();
      $sale  = $child->get_sale_price();

      $percentage = $price != 0 && ! empty( $sale ) ? ( ( $price - $sale ) / $price * 100 ) : $highest_percentage;

      if ( $percentage >= $highest_percentage ) {
        $highest_percentage = $percentage;
        $regular_price      = $product->get_variation_regular_price( 'min' );
        $sale_price         = $product->get_variation_sale_price( 'min' );
      }
    }
  }

  $label = str_replace( '{percentage}', round( $highest_percentage, apply_filters( 'wapl_filter_discount_round', 1 ) ) . '%', $label );
  $label = str_replace( '{discount}', wc_price( (float) $regular_price - (float) $sale_price ), $label );
  $label = str_replace( '{price}', wc_price( $regular_price ), $label );
  $label = str_replace( '{saleprice}', wc_price( $sale_price ), $label );
  $label = str_replace( '{delprice}', '<del>' . wc_price( $regular_price ) . '</del>', $label );

  return $label;
});