支払いの流れに関して

	/**
	 * Process an order that does require payment.
	 *
	 * @since 3.0.0
	 * @param int    $order_id       Order ID.
	 * @param string $payment_method Payment method.
	 */
	protected function process_order_payment( $order_id, $payment_method ) {
		$available_gateways = WC()->payment_gateways->get_available_payment_gateways();

		if ( ! isset( $available_gateways[ $payment_method ] ) ) {
			return;
		}

		// Store Order ID in session so it can be re-used after payment failure.
		WC()->session->set( 'order_awaiting_payment', $order_id );

		// Process Payment.
		$result = $available_gateways[ $payment_method ]->process_payment( $order_id );

		// Redirect to success/confirmation/payment page.
		if ( isset( $result['result'] ) && 'success' === $result['result'] ) {
			$result['order_id'] = $order_id;

			$result = apply_filters( 'woocommerce_payment_successful_result', $result, $order_id );

			if ( ! wp_doing_ajax() ) {
				// phpcs:ignore WordPress.Security.SafeRedirect.wp_redirect_wp_redirect
				wp_redirect( $result['redirect'] );
				exit;
			}

			wp_send_json( $result );
		}
	}

	/**
	 * Process the checkout after the confirm order button is pressed.
	 *
	 * @throws Exception When validation fails.
	 */
	public function process_checkout() {
		try {
			$nonce_value    = wc_get_var( $_REQUEST['woocommerce-process-checkout-nonce'], wc_get_var( $_REQUEST['_wpnonce'], '' ) ); // phpcs:ignore
			$expiry_message = sprintf(
				/* translators: %s: shop cart url */
				__( 'Sorry, your session has expired. <a href="%s" class="wc-backward">Return to shop</a>', 'woocommerce' ),
				esc_url( wc_get_page_permalink( 'shop' ) )
			);

			if ( empty( $nonce_value ) || ! wp_verify_nonce( $nonce_value, 'woocommerce-process_checkout' ) ) {
				// If the cart is empty, the nonce check failed because of session expiry.
				if ( WC()->cart->is_empty() ) {
					throw new Exception( $expiry_message );
				}

				WC()->session->set( 'refresh_totals', true );
				throw new Exception( __( 'We were unable to process your order, please try again.', 'woocommerce' ) );
			}

			wc_maybe_define_constant( 'WOOCOMMERCE_CHECKOUT', true );
			wc_set_time_limit( 0 );

			do_action( 'woocommerce_before_checkout_process' );

			if ( WC()->cart->is_empty() ) {
				throw new Exception( $expiry_message );
			}

			do_action( 'woocommerce_checkout_process' );

			$errors      = new WP_Error();
			$posted_data = $this->get_posted_data();

			// Update session for customer and totals.
			$this->update_session( $posted_data );

			// Validate posted data and cart items before proceeding.
			$this->validate_checkout( $posted_data, $errors );

			foreach ( $errors->errors as $code => $messages ) {
				$data = $errors->get_error_data( $code );
				foreach ( $messages as $message ) {
					wc_add_notice( $message, 'error', $data );
				}
			}

			if ( empty( $posted_data['woocommerce_checkout_update_totals'] ) && 0 === wc_notice_count( 'error' ) ) {
				$this->process_customer( $posted_data );
				$order_id = $this->create_order( $posted_data );
				$order    = wc_get_order( $order_id );

				if ( is_wp_error( $order_id ) ) {
					throw new Exception( $order_id->get_error_message() );
				}

				if ( ! $order ) {
					throw new Exception( __( 'Unable to create order.', 'woocommerce' ) );
				}

				do_action( 'woocommerce_checkout_order_processed', $order_id, $posted_data, $order );

				/**
				 * Note that woocommerce_cart_needs_payment is only used in
				 * WC_Checkout::process_checkout() to keep backwards compatibility.
				 * Use woocommerce_order_needs_payment instead.
				 *
				 * Note that at this point you can't rely on the Cart Object anymore,
				 * since it could be empty see:
				 * https://github.com/woocommerce/woocommerce/issues/24631
				 */
				if ( apply_filters( 'woocommerce_cart_needs_payment', $order->needs_payment(), WC()->cart ) ) {
					$this->process_order_payment( $order_id, $posted_data['payment_method'] );
				} else {
					$this->process_order_without_payment( $order_id );
				}
			}
		} catch ( Exception $e ) {
			wc_add_notice( $e->getMessage(), 'error' );
		}
		$this->send_ajax_failure_response();
	}