Use the new subquery in fetch_sms_billing_for_organisation()

This is so we have granular data about billable units and costs
so that we can handle multiple sms rates within one financial
year.

We also cast chargeable_units_used_so_far in that subquery
to integer so we don't have type mismatch.

Co-authored-by: Leo Hemsted <leo.hemsted@digital.cabinet-office.gov.uk>

app/dao/fact_billing_dao.py

@@ -720,52 +720,42 @@ def fetch_email_usage_for_organisation(organisation_id, start_date, end_date):
     return query.all()
 
 
-def fetch_sms_billing_for_organisation(organisation_id, start_date, end_date):
+def fetch_sms_billing_for_organisation(organisation_id, financial_year):
     # ASSUMPTION: AnnualBilling has been populated for year.
-    allowance_left_at_start_date_query = fetch_sms_free_allowance_remainder_until_date(start_date).subquery()
+    ft_billing_subquery = query_organisation_sms_usage_for_year(organisation_id, financial_year).subquery()
 
-    sms_billable_units = func.coalesce(func.sum(FactBilling.billable_units * FactBilling.rate_multiplier), 0)
+    sms_billable_units = func.sum(func.coalesce(ft_billing_subquery.c.chargeable_units, 0))
 
     # subtract sms_billable_units units accrued since report's start date to get up-to-date
     # allowance remainder
-    sms_allowance_left = func.greatest(allowance_left_at_start_date_query.c.sms_remainder - sms_billable_units, 0)
+    sms_allowance_left = func.greatest(AnnualBilling.free_sms_fragment_limit - sms_billable_units, 0)
 
-    # billable units here are for period between start date and end date only, so to see
+    chargeable_sms = func.sum(ft_billing_subquery.c.charged_units)
-    # how many are chargeable, we need to see how much free allowance was used up in the
+    sms_cost = func.sum(ft_billing_subquery.c.cost)
-    # period up until report's start date and then do a subtraction
-    chargeable_sms = func.greatest(sms_billable_units - allowance_left_at_start_date_query.c.sms_remainder, 0)
-    sms_cost = chargeable_sms * FactBilling.rate
 
     query = db.session.query(
         Service.name.label("service_name"),
         Service.id.label("service_id"),
-        func.coalesce(allowance_left_at_start_date_query.c.free_sms_fragment_limit, 0).label('free_sms_fragment_limit'),
+        AnnualBilling.free_sms_fragment_limit,
-        func.coalesce(FactBilling.rate, 0).label('sms_rate'),
         func.coalesce(sms_allowance_left, 0).label("sms_remainder"),
         func.coalesce(sms_billable_units, 0).label('sms_billable_units'),
         func.coalesce(chargeable_sms, 0).label("chargeable_billable_sms"),
         func.coalesce(sms_cost, 0).label('sms_cost'),
-        Service.active.label("active")
+        Service.active
     ).select_from(
         Service
     ).outerjoin(
-        allowance_left_at_start_date_query, Service.id == allowance_left_at_start_date_query.c.service_id
+        AnnualBilling,
+        and_(Service.id == AnnualBilling.service_id, AnnualBilling.financial_year_start == financial_year)
     ).outerjoin(
-        FactBilling, and_(
+        ft_billing_subquery, Service.id == ft_billing_subquery.c.service_id
-            Service.id == FactBilling.service_id,
-            FactBilling.bst_date >= start_date,
-            FactBilling.bst_date < end_date,
-            FactBilling.notification_type == SMS_TYPE,
-        )
     ).filter(
         Service.organisation_id == organisation_id,
         Service.restricted.is_(False)
     ).group_by(
         Service.id,
         Service.name,
-        allowance_left_at_start_date_query.c.free_sms_fragment_limit,
+        AnnualBilling.free_sms_fragment_limit
-        allowance_left_at_start_date_query.c.sms_remainder,
-        FactBilling.rate,
     ).order_by(
         Service.name
     )
@@ -856,7 +846,7 @@ def fetch_usage_year_for_organisation(organisation_id, year):
             'emails_sent': 0,
             'active': service.active
         }
-    sms_usages = fetch_sms_billing_for_organisation(organisation_id, year_start, year_end)
+    sms_usages = fetch_sms_billing_for_organisation(organisation_id, year)
     letter_usages = fetch_letter_costs_for_organisation(organisation_id, year_start, year_end)
     email_usages = fetch_email_usage_for_organisation(organisation_id, year_start, year_end)
     for usage in sms_usages:

tests/app/dao/test_fact_billing_dao.py

@@ -906,6 +906,95 @@ def test_fetch_usage_year_for_organisation_populates_ft_billing_for_today(notify
     assert FactBilling.query.count() == 1
 
 
+@freeze_time('2022-05-01 13:30')
+def test_fetch_usage_year_for_organisation_calculates_cost_from_multiple_rates(notify_db_session):
+    old_rate_date = date(2022, 4, 29)
+    new_rate_date = date(2022, 5, 1)
+    current_year = datetime.utcnow().year
+
+    org = create_organisation(name='Organisation 1')
+
+    service_1 = create_service(restricted=False, service_name="Service 1")
+    dao_add_service_to_organisation(service=service_1, organisation_id=org.id)
+    sms_template_1 = create_template(service=service_1)
+    create_ft_billing(
+        bst_date=old_rate_date, template=sms_template_1, rate=2,
+        billable_unit=4, notifications_sent=4
+    )
+    create_ft_billing(
+        bst_date=new_rate_date, template=sms_template_1, rate=3,
+        billable_unit=2, notifications_sent=2
+    )
+    create_annual_billing(service_id=service_1.id, free_sms_fragment_limit=3, financial_year_start=current_year)
+
+    results = fetch_usage_year_for_organisation(organisation_id=org.id, year=current_year)
+
+    assert len(results) == 1
+    assert results[str(service_1.id)]['free_sms_limit'] == 3
+    assert results[str(service_1.id)]['sms_remainder'] == 0
+    assert results[str(service_1.id)]['sms_billable_units'] == 6
+    assert results[str(service_1.id)]['chargeable_billable_sms'] == 3
+    assert results[str(service_1.id)]['sms_cost'] == 8.0
+
+
+@freeze_time('2022-05-01 13:30')
+def test_fetch_usage_year_for_organisation_when_no_usage(notify_db_session):
+    current_year = datetime.utcnow().year
+
+    org = create_organisation(name='Organisation 1')
+
+    service_1 = create_service(restricted=False, service_name="Service 1")
+    dao_add_service_to_organisation(service=service_1, organisation_id=org.id)
+    create_annual_billing(service_id=service_1.id, free_sms_fragment_limit=3, financial_year_start=current_year)
+
+    results = fetch_usage_year_for_organisation(organisation_id=org.id, year=current_year)
+
+    assert len(results) == 1
+    assert results[str(service_1.id)]['free_sms_limit'] == 3
+    assert results[str(service_1.id)]['sms_remainder'] == 3
+    assert results[str(service_1.id)]['sms_billable_units'] == 0
+    assert results[str(service_1.id)]['chargeable_billable_sms'] == 0
+    assert results[str(service_1.id)]['sms_cost'] == 0.0
+
+
+@freeze_time('2022-05-01 13:30')
+def test_fetch_usage_year_for_organisation_only_queries_present_year(notify_db_session):
+    current_year = datetime.utcnow().year
+    last_year = current_year - 1
+    date_two_years_ago = date(2021, 3, 31)
+    date_in_last_financial_year = date(2022, 3, 31)
+    date_in_this_year = date.today()
+
+    org = create_organisation(name='Organisation 1')
+
+    service_1 = create_service(restricted=False, service_name="Service 1")
+    dao_add_service_to_organisation(service=service_1, organisation_id=org.id)
+    sms_template_1 = create_template(service=service_1)
+
+    create_ft_billing(
+        bst_date=date_two_years_ago, template=sms_template_1, rate=1,
+        billable_unit=2, notifications_sent=2
+    )
+    create_ft_billing(
+        bst_date=date_in_last_financial_year, template=sms_template_1, rate=1,
+        billable_unit=4, notifications_sent=4
+    )
+    create_ft_billing(
+        bst_date=date_in_this_year, template=sms_template_1, rate=1,
+        billable_unit=8, notifications_sent=8
+    )
+    create_annual_billing(service_id=service_1.id, free_sms_fragment_limit=4, financial_year_start=last_year - 1)
+    create_annual_billing(service_id=service_1.id, free_sms_fragment_limit=0, financial_year_start=last_year)
+    create_annual_billing(service_id=service_1.id, free_sms_fragment_limit=8, financial_year_start=current_year)
+
+    results = fetch_usage_year_for_organisation(organisation_id=org.id, year=last_year)
+
+    assert len(results) == 1
+    assert results[str(service_1.id)]['sms_billable_units'] == 4
+    assert results[str(service_1.id)]['chargeable_billable_sms'] == 4
+    assert results[str(service_1.id)]['sms_cost'] == 4.0
+
+
 @freeze_time('2020-02-27 13:30')
 def test_fetch_usage_year_for_organisation_only_returns_data_for_live_services(notify_db_session):
     org = create_organisation(name='Organisation without live services')