feat: voucher purchase flow

src/Service/PurchaseFlowResolver.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+use App\Model\PurchaseFlow;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Tells the login page which purchase flow, if any, it is the entry to.
+ *
+ * Both a booking and a voucher purchase can be pending in the same session, e.g. when they were
+ * started in two tabs. The one started last wins, which is what the visitor just clicked.
+ */
+class PurchaseFlowResolver
+{
+    public const string LAST_STARTED_KEY = 'purchase_flow_last_started';
+
+    public function markStarted(Request $request, PurchaseFlow $flow): void
+    {
+        $request->getSession()->set(self::LAST_STARTED_KEY, $flow->value);
+    }
+
+    public function resolvePending(Request $request): ?PurchaseFlow
+    {
+        $session = $request->getSession();
+        $hasBooking = $session->has(BookingSessionManager::BOOKING_CREATE_KEY);
+        $hasVoucher = $session->has(VoucherPurchaseSessionManager::SESSION_KEY);
+
+        if (true === $hasBooking && true === $hasVoucher) {
+            return PurchaseFlow::tryFrom((string) $session->get(self::LAST_STARTED_KEY)) ?? PurchaseFlow::Booking;
+        }
+
+        return match (true) {
+            $hasBooking => PurchaseFlow::Booking,
+            $hasVoucher => PurchaseFlow::Voucher,
+            default => null,
+        };
+    }
+}