public function read_variation_attributes( &$product ) {
		global $wpdb;

		$variation_attributes = array();
		$attributes           = $product->get_attributes();
		$child_ids            = $product->get_children();
		$cache_key            = WC_Cache_Helper::get_cache_prefix( 'product_' . $product->get_id() ) . 'product_variation_attributes_' . $product->get_id();
		$cache_group          = 'products';
		$cached_data          = wp_cache_get( $cache_key, $cache_group );

		if ( false !== $cached_data ) {
			return $cached_data;
		}

		if ( ! empty( $attributes ) ) {
			foreach ( $attributes as $attribute ) {
				if ( empty( $attribute['is_variation'] ) ) {
					continue;
				}

				// Get possible values for this attribute, for only visible variations.
				if ( ! empty( $child_ids ) ) {
					$format     = array_fill( 0, count( $child_ids ), '%d' );
					$query_in   = '(' . implode( ',', $format ) . ')';
					$query_args = array( 'attribute_name' => wc_variation_attribute_name( $attribute['name'] ) ) + $child_ids;
					$values     = array_unique(
						$wpdb->get_col(
							$wpdb->prepare( // wpcs: PreparedSQLPlaceholders replacement count ok.
								"SELECT meta_value FROM {$wpdb->postmeta} WHERE meta_key = %s AND post_id IN {$query_in}", // @codingStandardsIgnoreLine.
								$query_args
							)
						)
					);
				} else {
					$values = array();
				}

				// Empty value indicates that all options for given attribute are available.
				if ( in_array( null, $values, true ) || in_array( '', $values, true ) || empty( $values ) ) {
					$values = $attribute['is_taxonomy'] ? wc_get_object_terms( $product->get_id(), $attribute['name'], 'slug' ) : wc_get_text_attributes( $attribute['value'] );
					// Get custom attributes (non taxonomy) as defined.
				} elseif ( ! $attribute['is_taxonomy'] ) {
					$text_attributes          = wc_get_text_attributes( $attribute['value'] );
					$assigned_text_attributes = $values;
					$values                   = array();

					// Pre 2.4 handling where 'slugs' were saved instead of the full text attribute.
					if ( version_compare( get_post_meta( $product->get_id(), '_product_version', true ), '2.4.0', '<' ) ) {
						$assigned_text_attributes = array_map( 'sanitize_title', $assigned_text_attributes );
						foreach ( $text_attributes as $text_attribute ) {
							if ( in_array( sanitize_title( $text_attribute ), $assigned_text_attributes, true ) ) {
								$values[] = $text_attribute;
							}
						}
					} else {
						foreach ( $text_attributes as $text_attribute ) {
							if ( in_array( $text_attribute, $assigned_text_attributes, true ) ) {
								$values[] = $text_attribute;
							}
						}
					}
				}
				$variation_attributes[ $attribute['name'] ] = array_unique( $values );
			}
		}

		wp_cache_set( $cache_key, $variation_attributes, $cache_group );

		return $variation_attributes;
	}