Payment Gateway: Add tax support (#172)

src/payment_gateway/changelog.d/20241107_212223_jkachel_add_tax.md

@@ -0,0 +1,43 @@
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+-->
+
+<!--
+### Removed
+
+- A bullet item for the Removed category.
+
+-->
+
+### Added
+
+- Adds support for tax collection.
+- Bumps CyberSource REST Client package to at least 0.0.54.
+- Adds a helper for quantizing decimals for currency amounts.
+
+<!--
+### Changed
+
+- A bullet item for the Changed category.
+
+-->
+<!--
+### Deprecated
+
+- A bullet item for the Deprecated category.
+
+-->
+<!--
+### Fixed
+
+- A bullet item for the Fixed category.
+
+-->
+<!--
+### Security
+
+- A bullet item for the Security category.
+
+-->

src/payment_gateway/mitol/payment_gateway/api.py

@@ -34,7 +34,11 @@
     InvalidTransactionException,
     RefundDuplicateException,
 )
-from mitol.payment_gateway.payment_utils import clean_request_data, strip_nones
+from mitol.payment_gateway.payment_utils import (
+    clean_request_data,
+    quantize_decimal,
+    strip_nones,
+)
 
 
 @dataclass
@@ -362,6 +366,10 @@ class CyberSourcePaymentGateway(
     def _generate_line_items(self, cart):
         """
         Generates CyberSource-formatted line items based on what's in the cart.
+
+        The unit price being stored should be the unit price after any discounts
+        have been applied. The tax amount should be the _total_ for the line.
+
         Args:
             cart:   List of CartItems
 
@@ -370,9 +378,11 @@ def _generate_line_items(self, cart):
         """  # noqa: D401
         lines = {}
         cart_total = 0
+        tax_total = 0
 
         for i, line in enumerate(cart):
             cart_total += line.quantity * line.unitprice
+            tax_total += line.taxable
 
             lines[f"item_{i}_code"] = str(line.code)
             lines[f"item_{i}_name"] = str(line.name)[:254]
@@ -381,7 +391,7 @@ def _generate_line_items(self, cart):
             lines[f"item_{i}_tax_amount"] = str(line.taxable)
             lines[f"item_{i}_unit_price"] = str(line.unitprice)
 
-        return (lines, cart_total)
+        return (lines, cart_total, tax_total)
 
     def _generate_cybersource_sa_signature(self, payload):
         """
@@ -438,7 +448,7 @@ def prepare_checkout(
         stored anywhere.
         """  # noqa: D401
 
-        (line_items, total) = self._generate_line_items(order.items)
+        (line_items, total, tax_total) = self._generate_line_items(order.items)
 
         formatted_merchant_fields = {}
 
@@ -455,7 +465,8 @@ def prepare_checkout(
 
         payload = {
             "access_key": settings.MITOL_PAYMENT_GATEWAY_CYBERSOURCE_ACCESS_KEY,
-            "amount": str(total),
+            "amount": str(quantize_decimal(total + tax_total)),
+            "tax_amount": str(quantize_decimal(tax_total)),
             "consumer_id": consumer_id,
             "currency": "USD",
             "locale": "en-us",

src/payment_gateway/mitol/payment_gateway/payment_utils.py

@@ -1,5 +1,7 @@
 """Utilities for the Payment Gateway"""
 
+from decimal import Decimal
+
 
 # To delete None values in Input Request Json body
 def clean_request_data(request_data):
@@ -21,3 +23,8 @@ def strip_nones(datasource):
             retval[key] = datasource[key]
 
     return retval
+
+
+def quantize_decimal(value, precision=2):
+    """Quantize a decimal value to the specified precision"""
+    return Decimal(value).quantize(Decimal("0.{}".format("0" * precision)))

src/payment_gateway/pyproject.toml

@@ -3,7 +3,7 @@ name = "mitol-django-payment-gateway"
 version = "2023.12.19"
 description = "Django application to handle payment processing"
 dependencies = [
-"cybersource-rest-client-python>=0.0.36",
+"cybersource-rest-client-python>=0.0.59",
 "django-stubs>=1.13.1",
 "django>=3.0",
 "mitol-django-common"

tests/mitol/payment_gateway/api/test_cybersource.py

@@ -5,6 +5,7 @@
 from collections import namedtuple
 from dataclasses import dataclass
 from datetime import datetime
+from decimal import Decimal
 from typing import Dict
 
 import pytest
@@ -81,10 +82,11 @@ def generate_test_cybersource_payload(order, cartitems, transaction_uuid):
     cancel_url = "https://duckduckgo.com"
 
     test_line_items = {}
-    test_total = 0
+    test_total = tax_total = 0
 
     for idx, line in enumerate(cartitems):
         test_total += line.quantity * line.unitprice
+        tax_total += line.taxable
 
         test_line_items[f"item_{idx}_code"] = str(line.code)
         test_line_items[f"item_{idx}_name"] = str(line.name)[:254]
@@ -97,7 +99,8 @@ def generate_test_cybersource_payload(order, cartitems, transaction_uuid):
 
     test_payload = {
         "access_key": settings.MITOL_PAYMENT_GATEWAY_CYBERSOURCE_ACCESS_KEY,
-        "amount": str(test_total),
+        "amount": str(Decimal(test_total + tax_total).quantize(Decimal("0.01"))),
+        "tax_amount": str(Decimal(tax_total).quantize(Decimal("0.01"))),
         "consumer_id": consumer_id,
         "currency": "USD",
         "locale": "en-us",
@@ -140,7 +143,14 @@ def test_invalid_payload_generation(order, cartitems):
     assert isinstance(checkout_data, TypeError)
 
 
-def test_cybersource_payload_generation(order, cartitems):
+@pytest.mark.parametrize(
+    ("with_tax"),
+    [
+        (True),
+        (False),
+    ],
+)
+def test_cybersource_payload_generation(order, cartitems, with_tax):
     """
     Starts a payment through the payment gateway, and then checks to make sure
     there's stuff in the payload that it generates. The transaction is not sent
@@ -151,6 +161,11 @@ def test_cybersource_payload_generation(order, cartitems):
     cancel_url = "https://duckduckgo.com"
     order.items = cartitems
 
+    # By default, the cart items will have tax.
+    if not with_tax:
+        for idx in range(len(order.items)):
+            order.items[idx].taxable = 0
+
     checkout_data = PaymentGateway.start_payment(
         MITOL_PAYMENT_GATEWAY_CYBERSOURCE,
         order,

tests/mitol/payment_gateway/utils/test_payment_utils.py

@@ -1,7 +1,13 @@
 """Tests for payment_gateway application utils"""  # noqa: INP001
 
+from decimal import Decimal
+
 import pytest
-from mitol.payment_gateway.payment_utils import clean_request_data, strip_nones
+from mitol.payment_gateway.payment_utils import (
+    clean_request_data,
+    quantize_decimal,
+    strip_nones,
+)
 
 
 @pytest.mark.parametrize(
@@ -44,3 +50,17 @@ def test_strip_nones():
     test_ds2 = strip_nones(ds2)
 
     assert test_ds2 == ds2
+
+
+def test_quantize_decimal():
+    """
+    Tests quantize_decimal to make sure that the decimal is quantized to
+    the correct precision.
+    """
+
+    test_decimal = 1.23456789
+    test_precision = 2
+
+    quantized_decimal = quantize_decimal(test_decimal, test_precision)
+
+    assert quantized_decimal == Decimal("1.23")

tests/testapp/factories.py

@@ -1,9 +1,10 @@
 """Test factories"""
 
 import string
+from decimal import Decimal
 
 import faker
-from factory import Factory, SubFactory, fuzzy
+from factory import Factory, LazyAttribute, SubFactory, fuzzy
 from factory.django import DjangoModelFactory
 from mitol.common.factories import UserFactory
 from mitol.digitalcredentials.factories import (
@@ -46,8 +47,12 @@ class Meta:
     code = fuzzy.FuzzyText(length=6)
     quantity = fuzzy.FuzzyInteger(1, 5, 1)
     name = FAKE.sentence(nb_words=3)
-    taxable = 0
     unitprice = fuzzy.FuzzyDecimal(1, 300, precision=2)
+    taxable = LazyAttribute(
+        lambda o: Decimal(o.unitprice * Decimal(FAKE.random_number(2) * 0.01)).quantize(
+            Decimal("0.01")
+        )
+    )
 
 
 class OrderFactory(Factory):