refactor(payment_methods): allow deletion of default payment method for a customer if only one pm exists (#4027)

Co-authored-by: hyperswitch-bot[bot] <148525504+hyperswitch-bot[bot]@users.noreply.github.com>

crates/router/src/core/payment_methods/cards.rs

@@ -3201,7 +3201,7 @@ pub async fn set_default_payment_method(
     )?;
 
     let customer_update = CustomerUpdate::UpdateDefaultPaymentMethod {
-        default_payment_method_id: Some(payment_method_id.to_owned()),
+        default_payment_method_id: Some(Some(payment_method_id.to_owned())),
     };
 
     // update the db with the default payment method id
@@ -3450,6 +3450,16 @@ pub async fn delete_payment_method(
         .await
         .to_not_found_response(errors::ApiErrorResponse::PaymentMethodNotFound)?;
 
+    let payment_methods_count = db
+        .get_payment_method_count_by_customer_id_merchant_id_status(
+            &key.customer_id,
+            &merchant_account.merchant_id,
+            api_enums::PaymentMethodStatus::Active,
+        )
+        .await
+        .change_context(errors::ApiErrorResponse::InternalServerError)
+        .attach_printable("Failed to get a count of payment methods for a customer")?;
+
     let customer = db
         .find_customer_by_customer_id_merchant_id(
             &key.customer_id,
@@ -3461,7 +3471,8 @@ pub async fn delete_payment_method(
         .attach_printable("Customer not found for the payment method")?;
 
     utils::when(
-        customer.default_payment_method_id.as_ref() == Some(&pm_id.payment_method_id),
+        customer.default_payment_method_id.as_ref() == Some(&pm_id.payment_method_id)
+            && payment_methods_count > 1,
         || Err(errors::ApiErrorResponse::PaymentMethodDeleteFailed),
     )?;
 
@@ -3489,6 +3500,22 @@ pub async fn delete_payment_method(
     .await
     .to_not_found_response(errors::ApiErrorResponse::PaymentMethodNotFound)?;
 
+    if customer.default_payment_method_id.as_ref() == Some(&pm_id.payment_method_id) {
+        let customer_update = CustomerUpdate::UpdateDefaultPaymentMethod {
+            default_payment_method_id: Some(None),
+        };
+
+        db.update_customer_by_customer_id_merchant_id(
+            key.customer_id,
+            key.merchant_id,
+            customer_update,
+            &key_store,
+        )
+        .await
+        .change_context(errors::ApiErrorResponse::InternalServerError)
+        .attach_printable("Failed to update the default payment method id for the customer")?;
+    };
+
     Ok(services::ApplicationResponse::Json(
         api::PaymentMethodDeleteResponse {
             payment_method_id: key.payment_method_id,

crates/router/src/db/kafka_store.rs

@@ -1299,6 +1299,21 @@ impl PaymentMethodInterface for KafkaStore {
             .await
     }
 
+    async fn get_payment_method_count_by_customer_id_merchant_id_status(
+        &self,
+        customer_id: &str,
+        merchant_id: &str,
+        status: common_enums::PaymentMethodStatus,
+    ) -> CustomResult<i64, errors::StorageError> {
+        self.diesel_store
+            .get_payment_method_count_by_customer_id_merchant_id_status(
+                customer_id,
+                merchant_id,
+                status,
+            )
+            .await
+    }
+
     async fn find_payment_method_by_locker_id(
         &self,
         locker_id: &str,

crates/router/src/db/payment_method.rs

@@ -36,6 +36,13 @@ pub trait PaymentMethodInterface {
         limit: Option<i64>,
     ) -> CustomResult<Vec<storage::PaymentMethod>, errors::StorageError>;
 
+    async fn get_payment_method_count_by_customer_id_merchant_id_status(
+        &self,
+        customer_id: &str,
+        merchant_id: &str,
+        status: common_enums::PaymentMethodStatus,
+    ) -> CustomResult<i64, errors::StorageError>;
+
     async fn insert_payment_method(
         &self,
         payment_method_new: storage::PaymentMethodNew,
@@ -80,6 +87,25 @@ impl PaymentMethodInterface for Store {
             .into_report()
     }
 
+    #[instrument(skip_all)]
+    async fn get_payment_method_count_by_customer_id_merchant_id_status(
+        &self,
+        customer_id: &str,
+        merchant_id: &str,
+        status: common_enums::PaymentMethodStatus,
+    ) -> CustomResult<i64, errors::StorageError> {
+        let conn = connection::pg_connection_read(self).await?;
+        storage::PaymentMethod::get_count_by_customer_id_merchant_id_status(
+            &conn,
+            customer_id,
+            merchant_id,
+            status,
+        )
+        .await
+        .map_err(Into::into)
+        .into_report()
+    }
+
     #[instrument(skip_all)]
     async fn insert_payment_method(
         &self,
@@ -204,6 +230,27 @@ impl PaymentMethodInterface for MockDb {
         }
     }
 
+    async fn get_payment_method_count_by_customer_id_merchant_id_status(
+        &self,
+        customer_id: &str,
+        merchant_id: &str,
+        status: common_enums::PaymentMethodStatus,
+    ) -> CustomResult<i64, errors::StorageError> {
+        let payment_methods = self.payment_methods.lock().await;
+        let count = payment_methods
+            .iter()
+            .filter(|pm| {
+                pm.customer_id == customer_id
+                    && pm.merchant_id == merchant_id
+                    && pm.status == status
+            })
+            .count();
+        count
+            .try_into()
+            .into_report()
+            .change_context(errors::StorageError::MockDbError)
+    }
+
     async fn insert_payment_method(
         &self,
         payment_method_new: storage::PaymentMethodNew,

crates/router/src/types/domain/customer.rs

@@ -118,7 +118,7 @@ pub enum CustomerUpdate {
         connector_customer: Option<serde_json::Value>,
     },
     UpdateDefaultPaymentMethod {
-        default_payment_method_id: Option<String>,
+        default_payment_method_id: Option<Option<String>>,
     },
 }