Show the discount on sale badges

<?php

add_filter(
	'woocommerce_sale_flash',
	static function ( $html, $post, $product ) {
		if ( ! $product instanceof WC_Product ) {
			return $html;
		}
		$percent = 0;
		if ( $product->is_type( 'variable' ) ) {
			$prices = $product->get_variation_prices( true );
			foreach ( $prices['regular_price'] as $id => $regular ) {
				$sale = (float) ( $prices['sale_price'][ $id ] ?? $regular );
				if ( (float) $regular > 0 && $sale < (float) $regular ) {
					$percent = max( $percent, (int) round( 100 * ( (float) $regular - $sale ) / (float) $regular ) );
				}
			}
		} elseif ( '' !== $product->get_sale_price() && (float) $product->get_regular_price() > 0 ) {
			$regular = (float) $product->get_regular_price();
			$percent = (int) round( 100 * ( $regular - (float) $product->get_sale_price() ) / $regular );
		}
		return $percent > 0 ? '<span class="onsale">-' . $percent . '%</span>' : $html;
	},
	10,
	3
);