Preselect the first payment option when the buyer holds no choice yet

src/Checkout/Ajax/Payment/OnePageCheckoutPaymentMethodsHandler.php

@@ -221,7 +221,7 @@ private function resolvePersistedSelection(array $paymentOptions): array
         $selectedPaymentSelectionKey = $this->getSelectedPaymentSelectionKey();
 
         if ($selectedPaymentModule === '' && $selectedPaymentSelectionKey === '') {
-            return ['', ''];
+            return $this->resolveDefaultSelection($paymentOptions);
         }
 
         if ($this->hasValidPersistedSelection($paymentOptions, $selectedPaymentSelectionKey, $selectedPaymentModule)) {
@@ -230,6 +230,40 @@ private function resolvePersistedSelection(array $paymentOptions): array
 
         $this->clearPersistedSelection();
 
+        return $this->resolveDefaultSelection($paymentOptions);
+    }
+
+    /**
+     * Default to the first available payment option when the buyer holds no (valid) choice yet.
+     *
+     * Merchants order payment modules by position, so the first option is the shop's preferred
+     * method; preselecting it lets most buyers proceed without a mandatory extra decision at an
+     * unselected list, while any other option stays one click away. The existing render and
+     * client-side confirmation paths for a server-selected option are reused as-is.
+     *
+     * @param array<string, mixed> $paymentOptions
+     *
+     * @return array{0: string, 1: string}
+     */
+    private function resolveDefaultSelection(array $paymentOptions): array
+    {
+        foreach ($paymentOptions as $moduleName => $moduleOptions) {
+            if (!is_array($moduleOptions)) {
+                continue;
+            }
+
+            foreach ($moduleOptions as $paymentOption) {
+                if (!is_array($paymentOption)) {
+                    continue;
+                }
+
+                return [
+                    (string) ($paymentOption['module_name'] ?? $moduleName),
+                    (string) ($paymentOption['selection_key'] ?? ''),
+                ];
+            }
+        }
+
         return ['', ''];
     }
 

tests/php/Unit/Checkout/Ajax/OpcPaymentMethodsHandlerTest.php

@@ -73,6 +73,61 @@ public function write(): void
         self::assertFalse($response['is_free']);
     }
 
+    public function testItDefaultsToTheFirstPaymentOptionWhenNoSelectionIsPersisted(): void
+    {
+        $firstOption = [
+            'module_name' => 'ps_checkpayment',
+            'call_to_action_text' => 'Pay by Check',
+            'action' => '/module/ps_checkpayment/validation',
+        ];
+        $secondOption = [
+            'module_name' => 'ps_wirepayment',
+            'call_to_action_text' => 'Wire payment',
+            'action' => '/module/ps_wirepayment/validation',
+        ];
+        $expectedSelectionKey = (new PaymentSelectionKeyBuilder())->buildSelectionKey($firstOption);
+
+        $context = CheckoutTestFixtures::context([
+            'cart' => CheckoutTestFixtures::pricedCart(42.0, ['id' => 1]),
+            'country' => CheckoutTestFixtures::country(),
+            'shop' => CheckoutTestFixtures::shop(1),
+        ]);
+        $context->cookie = new class {
+            public function __get(string $name)
+            {
+                return null;
+            }
+
+            public function __unset(string $name): void
+            {
+            }
+
+            public function write(): void
+            {
+            }
+        };
+
+        $finder = $this->getMockBuilder(\PaymentOptionsFinder::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['present'])
+            ->getMock();
+        $finder->method('present')->willReturn([
+            'ps_checkpayment' => [
+                0 => $firstOption,
+            ],
+            'ps_wirepayment' => [
+                0 => $secondOption,
+            ],
+        ]);
+
+        $handler = new OnePageCheckoutPaymentMethodsHandler($context, $finder);
+        $response = $handler->handle();
+
+        self::assertTrue($response['success']);
+        self::assertSame('ps_checkpayment', $response['selected_payment_module']);
+        self::assertSame($expectedSelectionKey, $response['selected_payment_selection_key']);
+    }
+
     public function testItReturnsStructuredErrorWhenCartIsMissing(): void
     {
         $context = CheckoutTestFixtures::context([