Add support for processing refunds

Signed-off-by: Musale Martin <martinmshale@gmail.com>

pesapal_v3/_exceptions.py

@@ -36,3 +36,7 @@ class PesapalListIPNsError(PesapalAPIError):
 
 class PesapalGetTransactionStatusError(PesapalAPIError):
     """Pesapal get a transaction status error."""
+
+
+class PesapalRefundError(PesapalAPIError):
+    """Pesapa refund request error."""

pesapal_v3/_pesapal.py

@@ -5,15 +5,25 @@
 
 import httpx
 
-from pesapal_v3._exceptions import (PesapalAuthError,
-                                    PesapalGetTransactionStatusError,
-                                    PesapalIPNURLRegError,
-                                    PesapalListIPNsError,
-                                    PesapalSubmitOrderRequestError)
-from pesapal_v3._types import (AccessToken, Environment, IPNRegistration,
-                               OrderRequest, OrderRequestResponse,
-                               PesapalError, SubscriptionDetails,
-                               TransactionStatus)
+from pesapal_v3._exceptions import (
+    PesapalAuthError,
+    PesapalGetTransactionStatusError,
+    PesapalIPNURLRegError,
+    PesapalListIPNsError,
+    PesapalSubmitOrderRequestError,
+    PesapalRefundError,
+)
+from pesapal_v3._types import (
+    AccessToken,
+    Environment,
+    IPNRegistration,
+    OrderRequest,
+    OrderRequestResponse,
+    PesapalError,
+    TransactionStatus,
+    Refund,
+    RefundResponse,
+)
 
 
 class Pesapal:
@@ -199,3 +209,29 @@ def get_transaction_status(self, *, order_tracking_id: str) -> TransactionStatus
             error_msg = PesapalError(**error)
             raise PesapalGetTransactionStatusError(error=error_msg, status=status)
         return TransactionStatus(**response)
+
+    def refund_request(self, *, refund: Refund) -> None:
+        """Perform a refund request.
+
+        Arguments:
+            refund(Refund): the refund details.
+        """
+        if not refund:
+            raise ValueError("refund cannot be empty.")
+
+        self._refresh_token()
+        with httpx.Client(base_url=self._base_url) as client:
+            client_resp = client.post(
+                "/Transactions/RefundRequest",
+                headers=self._headers,
+                json=refund,
+            )
+            response = client_resp.json()
+        error = response.get("error", None)
+        status = response.get("status", "500")
+        print(response)
+
+        if status != "200" and error:
+            error_msg = PesapalError(**error)
+            raise PesapalRefundError(error=error_msg, status=status)
+        return RefundResponse(**response)

pesapal_v3/_types.py

@@ -116,3 +116,19 @@ class TransactionStatus(NamedTuple):
     merchant_reference: str
     error: Optional[PesapalError]
     status: str
+
+
+class Refund(NamedTuple):
+    """Refund request payload"""
+
+    confirmation_code: str
+    amount: float
+    username: str
+    remarks: str
+
+
+class RefundResponse(NamedTuple):
+    """A refund response."""
+
+    status: str
+    message: str