refactor(payment_method_data): send optional billing details in response (#4569)

crates/api_models/src/payments.rs

@@ -2626,7 +2626,9 @@ where
     S: Serializer,
 {
     if let Some(payment_method_data_response) = payment_method_data_response {
-        match payment_method_data_response.payment_method_data {
+        if let Some(payment_method_data) = payment_method_data_response.payment_method_data.as_ref()
+        {
+            match payment_method_data {
                 PaymentMethodDataResponse::Reward {} => serializer.serialize_str("reward"),
                 PaymentMethodDataResponse::BankDebit {}
                 | PaymentMethodDataResponse::BankRedirect {}
@@ -2645,6 +2647,10 @@ where
                     payment_method_data_response.serialize(serializer)
                 }
             }
+        } else {
+            // Can serialize directly because there is no `payment_method_data`
+            payment_method_data_response.serialize(serializer)
+        }
     } else {
         serializer.serialize_none()
     }
@@ -2675,7 +2681,7 @@ pub enum PaymentMethodDataResponse {
 pub struct PaymentMethodDataResponseWithBilling {
     // The struct is flattened in order to provide backwards compatibility
     #[serde(flatten)]
-    pub payment_method_data: PaymentMethodDataResponse,
+    pub payment_method_data: Option<PaymentMethodDataResponse>,
     pub billing: Option<Address>,
 }
 
@@ -4808,6 +4814,68 @@ mod payments_request_api_contract {
             Some(PaymentMethodData::Reward)
         );
     }
+
+    #[test]
+    fn test_payment_method_data_with_payment_method_billing() {
+        let payments_request = r#"
+        {
+            "amount": 6540,
+            "currency": "USD",
+            "payment_method_data": {
+                "billing": {
+                    "address": {
+                        "line1": "1467",
+                        "line2": "Harrison Street",
+                        "city": "San Fransico",
+                        "state": "California",
+                        "zip": "94122",
+                        "country": "US",
+                        "first_name": "Narayan",
+                        "last_name": "Bhat"
+                    }
+                }
+            }
+        }
+        "#;
+
+        let payments_request = serde_json::from_str::<PaymentsRequest>(payments_request);
+        assert!(payments_request.is_ok());
+        assert!(payments_request
+            .unwrap()
+            .payment_method_data
+            .unwrap()
+            .billing
+            .is_some());
+    }
+}
+
+#[cfg(test)]
+mod payments_response_api_contract {
+    #![allow(clippy::unwrap_used)]
+    use super::*;
+
+    #[derive(Debug, serde::Serialize)]
+    struct TestPaymentsResponse {
+        #[serde(serialize_with = "serialize_payment_method_data_response")]
+        payment_method_data: Option<PaymentMethodDataResponseWithBilling>,
+    }
+
+    #[test]
+    fn test_reward_payment_response() {
+        let payment_method_response_with_billing = PaymentMethodDataResponseWithBilling {
+            payment_method_data: Some(PaymentMethodDataResponse::Reward {}),
+            billing: None,
+        };
+
+        let payments_response = TestPaymentsResponse {
+            payment_method_data: Some(payment_method_response_with_billing),
+        };
+
+        let expected_response = r#"{"payment_method_data":"reward"}"#;
+
+        let stringified_payments_response = payments_response.encode_to_string_of_json();
+        assert_eq!(stringified_payments_response.unwrap(), expected_response);
+    }
 }
 
 /// Set of tests to extract billing details from payment method data

crates/router/src/compatibility/stripe/payment_intents/types.rs

@@ -527,7 +527,9 @@ impl From<payments::PaymentsResponse> for StripePaymentIntentResponse {
             capture_on: resp.capture_on,
             capture_method: resp.capture_method,
             payment_method: resp.payment_method,
-            payment_method_data: resp.payment_method_data.map(|pmd| pmd.payment_method_data),
+            payment_method_data: resp
+                .payment_method_data
+                .and_then(|pmd| pmd.payment_method_data),
             payment_token: resp.payment_token,
             shipping: resp.shipping,
             billing: resp.billing,

crates/router/src/core/payments/transformers.rs

@@ -463,14 +463,17 @@ where
     let payment_method_data =
         additional_payment_method_data.map(api::PaymentMethodDataResponse::from);
 
-    let payment_method_data_response = payment_method_data.map(|payment_method_data| {
+    let payment_method_data_response = (payment_method_data.is_some()
-        api_models::payments::PaymentMethodDataResponseWithBilling {
+        || payment_data
+            .address
+            .get_request_payment_method_billing()
+            .is_some())
+    .then_some(api_models::payments::PaymentMethodDataResponseWithBilling {
         payment_method_data,
         billing: payment_data
             .address
             .get_request_payment_method_billing()
             .cloned(),
-        }
     });
 
     let mut headers = connector_http_status_code