public function apply_coupon( $raw_coupon ) {
		if ( is_a( $raw_coupon, 'WC_Coupon' ) ) {
			$coupon = $raw_coupon;
		} elseif ( is_string( $raw_coupon ) ) {
			$code   = wc_format_coupon_code( $raw_coupon );
			$coupon = new WC_Coupon( $code );

			if ( $coupon->get_code() !== $code ) {
				return new WP_Error( 'invalid_coupon', __( 'Invalid coupon code', 'woocommerce' ) );
			}
		} else {
			return new WP_Error( 'invalid_coupon', __( 'Invalid coupon', 'woocommerce' ) );
		}

		// Check to make sure coupon is not already applied.
		$applied_coupons = $this->get_items( 'coupon' );
		foreach ( $applied_coupons as $applied_coupon ) {
			if ( $applied_coupon->get_code() === $coupon->get_code() ) {
				return new WP_Error( 'invalid_coupon', __( 'Coupon code already applied!', 'woocommerce' ) );
			}
		}

		$discounts = new WC_Discounts( $this );
		$applied   = $discounts->apply_coupon( $coupon );

		if ( is_wp_error( $applied ) ) {
			return $applied;
		}

		$data_store = $coupon->get_data_store();

		// Check specific for guest checkouts here as well since WC_Cart handles that seperately in check_customer_coupons.
		if ( $data_store && 0 === $this->get_customer_id() ) {
			$usage_count = $data_store->get_usage_by_email( $coupon, $this->get_billing_email() );
			if ( 0 < $coupon->get_usage_limit_per_user() && $usage_count >= $coupon->get_usage_limit_per_user() ) {
				return new WP_Error(
					'invalid_coupon',
					$coupon->get_coupon_error( 106 ),
					array(
						'status' => 400,
					)
				);
			}
		}

		$this->set_coupon_discount_amounts( $discounts );
		$this->save();

		// Recalculate totals and taxes.
		$this->recalculate_coupons();

		// Record usage so counts and validation is correct.
		$used_by = $this->get_user_id();

		if ( ! $used_by ) {
			$used_by = $this->get_billing_email();
		}

		$coupon->increase_usage_count( $used_by );

		return true;
	}