feat: create instalments when calculating benefit (#3479)

backend/benefit/calculator/models.py

@@ -864,6 +864,12 @@ class Instalment(UUIDModel, TimeStampedModel):
         blank=True,
     )
 
+    def __str__(self):
+        return f"Instalment of {self.amount}€, \
+number {self.instalment_number}/{self.calculation.instalments.count()} \
+for application {self.calculation.application.application_number}, \
+due in {self.due_date}, status: {self.status}."
+
     class Meta:
         db_table = "bf_calculator_instalment"
         verbose_name = _("instalment")

backend/benefit/calculator/rules.py

@@ -6,6 +6,7 @@
 
 from django.conf import settings
 from django.db import transaction
+from django.utils import timezone
 
 from applications.enums import ApplicationStatus, BenefitType, PaySubsidyGranted
 from calculator.enums import DescriptionType, RowType
@@ -16,6 +17,7 @@
     DescriptionRow,
     EmployeeBenefitMonthlyRow,
     EmployeeBenefitTotalRow,
+    Instalment,
     ManualOverrideTotalRow,
     PaySubsidy,
     PaySubsidyMonthlyRow,
@@ -41,6 +43,7 @@ class HelsinkiBenefitCalculator:
     def __init__(self, calculation: Calculation):
         self.calculation = calculation
         self._row_counter = 0
+        self.instalment_threshold = settings.INSTALMENT_THRESHOLD
 
     def _get_change_days(
         self, pay_subsidies, training_compensations, start_date, end_date
@@ -156,19 +159,61 @@ def can_calculate(self):
             return False
         return True
 
+    def create_instalments(self, total_benefit_amount: decimal.Decimal) -> None:
+        """Create one instalment in the usual case,
+        two instalments if the benefit amount exceeds the threshold,
+        with the second instalment due 6 months later.
+        """
+        instalments = self._calculate_instalment_amounts(total_benefit_amount)
+        self._create_instalments(instalments)
+
+    def _calculate_instalment_amounts(
+        self, total_benefit_amount: decimal.Decimal
+    ) -> list[tuple[int, decimal.Decimal, datetime.datetime]]:
+        """Calculate the number of instalments and their amounts based on the total benefit.
+        Returns a list of tuples containing (instalment_number, amount, due_date).
+        """
+        if total_benefit_amount <= self.instalment_threshold:
+            return [(1, total_benefit_amount, timezone.now())]
+
+        second_instalment_amount = total_benefit_amount - self.instalment_threshold
+        return [
+            (1, self.instalment_threshold, timezone.now()),
+            (
+                2,
+                second_instalment_amount,
+                timezone.now() + datetime.timedelta(days=181),
+            ),
+        ]
+
+    def _create_instalments(
+        self, instalments: list[tuple[int, decimal.Decimal, datetime.datetime]]
+    ) -> None:
+        """Create instalment objects from the provided instalment data."""
+        for instalment_number, amount, due_date in instalments:
+            Instalment.objects.create(
+                calculation=self.calculation,
+                instalment_number=instalment_number,
+                amount=amount,
+                due_date=due_date,
+            )
+
     @transaction.atomic
     def calculate(self, override_status=False):
         if (
             self.calculation.application.status in self.CALCULATION_ALLOWED_STATUSES
             or override_status
         ):
             self.calculation.rows.all().delete()
+            self.calculation.instalments.all().delete()
             if self.can_calculate():
                 self.create_rows()
                 # the total benefit amount is stored in Calculation model, for easier processing.
-                self.calculation.calculated_benefit_amount = self.get_amount(
+                total_benefit_amount = self.get_amount(
                     RowType.HELSINKI_BENEFIT_TOTAL_EUR
                 )
+                self.calculation.calculated_benefit_amount = total_benefit_amount
+                self.create_instalments(total_benefit_amount)
             else:
                 self.calculation.calculated_benefit_amount = None
             self.calculation.save()

backend/benefit/calculator/tests/test_calculator_api.py

@@ -5,6 +5,7 @@
 
 import factory
 import pytest
+from django.utils import timezone
 
 from applications.api.v1.serializers.application import (
     ApplicantApplicationSerializer,
@@ -99,7 +100,10 @@ def test_application_try_retrieve_calculation_as_applicant(api_client, applicati
 
 
 def test_application_create_calculation_on_submit(
-    request, api_client, handler_api_client, application
+    request,
+    api_client,
+    handler_api_client,
+    application,
 ):
     # also test that calculation rows are not created yet,
     # as all fields are not filled yet.
@@ -691,3 +695,61 @@ def test_application_calculation_rows_id_exists(
     assert response.status_code == 200
     assert len(response.data["calculation"]["rows"]) > 1
     assert "id" in response.data["calculation"]["rows"][0].keys()
+
+
+@pytest.mark.parametrize(
+    "number_of_instalments, has_subsidies",
+    [(2, False), (1, True)],
+)
+def test_application_calculation_instalments(
+    handling_application, settings, number_of_instalments, has_subsidies
+):
+    settings.PAYMENT_INSTALMENTS_ENABLED = True
+    settings.INSTALMENT_THRESHOLD = 9600
+    settings.SALARY_BENEFIT_NEW_MAX = 1500
+
+    if has_subsidies is False:
+        handling_application.pay_subsidies.all().delete()
+        assert handling_application.pay_subsidies.count() == 0
+        handling_application.pay_subsidy_granted = PaySubsidyGranted.NOT_GRANTED
+        handling_application.save()
+
+        handling_application.calculation.start_date = datetime.now()
+        handling_application.calculation.end_date = (
+            handling_application.start_date + timedelta(weeks=52)
+        )
+        handling_application.calculation.save()
+
+    handling_application.calculation.init_calculator()
+    handling_application.calculation.calculate()
+
+    assert handling_application.calculation.instalments.count() == number_of_instalments
+    instalment_1 = handling_application.calculation.instalments.all()[0]
+
+    assert instalment_1.due_date is not None
+
+    due_date = instalment_1.due_date
+    now_date = timezone.now().date()
+
+    assert due_date == now_date
+
+    assert due_date == now_date
+
+    if number_of_instalments == 1:
+        assert (
+            instalment_1.amount
+            == handling_application.calculation.calculated_benefit_amount
+        )
+
+    if number_of_instalments == 2:
+        assert instalment_1.amount == decimal.Decimal(settings.INSTALMENT_THRESHOLD)
+        instalment_2 = handling_application.calculation.instalments.all()[1]
+        assert (
+            instalment_2.amount
+            == handling_application.calculation.calculated_benefit_amount
+            - decimal.Decimal(settings.INSTALMENT_THRESHOLD)
+        )
+
+        due_date = instalment_2.due_date
+        future_date = timezone.now() + timedelta(days=181)
+        assert due_date == future_date.date()

backend/benefit/helsinkibenefit/settings.py

@@ -179,6 +179,7 @@
     TALPA_CALLBACK_ENABLED=(bool, False),
     PAYMENT_INSTALMENTS_ENABLED=(bool, False),
     SALARY_BENEFIT_NEW_MAX=(int, 1500),
+    INSTALMENT_THRESHOLD=(int, 9600),
 )
 if os.path.exists(env_file):
     env.read_env(env_file)
@@ -568,3 +569,4 @@
 TALPA_CALLBACK_ENABLED = env.bool("TALPA_CALLBACK_ENABLED")
 PAYMENT_INSTALMENTS_ENABLED = env.bool("PAYMENT_INSTALMENTS_ENABLED")
 SALARY_BENEFIT_NEW_MAX = env.int("SALARY_BENEFIT_NEW_MAX")
+INSTALMENT_THRESHOLD = env.int("INSTALMENT_THRESHOLD")