Do not redirect users after navigating back to order page.

includes/class-wc-gateway-payfast.php

@@ -194,6 +194,29 @@ public function __construct() {
 
 		// Add support for WooPayments multi-currency.
 		add_filter( 'woocommerce_currency', array( $this, 'filter_currency' ) );
+
+		add_filter( 'nocache_headers', array( $this, 'no_store_cache_headers' ) );
+	}
+
+	/**
+	 * Use the no-store, private cache directive on the order-pay endpoint.
+	 *
+	 * This prevents the browser caching the page even when the visitor has clicked
+	 * the back button. This is required to determine if a user has pressed back while
+	 * in the payfast gateway.
+	 *
+	 * @since x.x.x
+	 *
+	 * @param string[] $headers Array of caching headers.
+	 * @return string[] Modified caching headers.
+	 */
+	public function no_store_cache_headers( $headers ) {
+		if ( ! is_wc_endpoint_url( 'order-pay' ) ) {
+			return $headers;
+		}
+
+		$headers['Cache-Control'] = 'no-cache, must-revalidate, max-age=0, no-store, private';
+		return $headers;
 	}
 
 	/**
@@ -486,6 +509,29 @@ class="button cancel"
 				'</a>
 				<script type="text/javascript">
 					jQuery(function(){
+						// Feature detect.
+						if (
+							typeof PerformanceNavigationTiming !== "undefined" &&
+							typeof window.performance !== "undefined" &&
+							typeof performance.getEntriesByType === "function"
+						) {
+							var isBackForward = false;
+							var entries = performance.getEntriesByType("navigation");
+							entries.forEach((entry) => {
+								if (entry.type === "back_forward") {
+									isBackForward = true;
+								}
+							});
+							if (isBackForward) {
+								/*
+								 * Do not submit form on back or forward.
+								 * Ensure that the body is unblocked/not showing the redirect message.
+								 */
+								jQuery("body").unblock();
+								return;
+							}
+						}
+
 						jQuery("body").block(
 							{
 								message: "' . esc_html__( 'Thank you for your order. We are now redirecting you to Payfast to make payment.', 'woocommerce-gateway-payfast' ) . '",