make rebuild-ft-billing-for-day remove unused rows

if the billing data was incorrect and needs to be rebuilt, we should
remove old rows. Previously we were only upserting new rows, but old
no-longer-relevant rows were staying in the database. This commit
makes the flask command remove *all* rows for that service and day,
before inserting the rows from the original notification data after.

This commit doesn't change the existing nightly task, nor does it
change the upsert that happens upon viewing the usage page. In normal
usage, there should never be a case where the number of billable units
for a rate decreases. It should only ever increase, thus, never need to
be deleted

app/commands.py

@@ -19,7 +19,11 @@ from app.celery.service_callback_tasks import send_delivery_status_to_service
 from app.celery.letters_pdf_tasks import create_letters_pdf
 from app.config import QueueNames
 from app.dao.date_util import get_financial_year
-from app.dao.fact_billing_dao import fetch_billing_data_for_day, update_fact_billing
+from app.dao.fact_billing_dao import (
+    fetch_billing_data_for_day,
+    update_fact_billing,
+    delete_billing_data_for_service_for_day
+)
 from app.dao.monthly_billing_dao import (
     create_or_update_monthly_billing,
     get_monthly_billing_by_notification_type,
@@ -526,17 +530,34 @@ def rebuild_ft_billing_for_day(service_id, day):
     Rebuild the data in ft_billing for the given service_id and date
     """
     def rebuild_ft_data(process_day, service):
+        deleted_rows = delete_billing_data_for_service_for_day(process_day, service)
+        current_app.logger.info('deleted {} existing billing rows for {} on {}'.format(
+            deleted_rows,
+            service,
+            process_day
+        ))
         transit_data = fetch_billing_data_for_day(process_day=process_day, service_id=service)
+        # transit_data = every row that should exist
         for data in transit_data:
+            # upsert existing rows
             update_fact_billing(data, process_day)
+        current_app.logger.info('added/updated {} billing rows for {} on {}'.format(
+            len(transit_data),
+            service,
+            process_day
+        ))
+
     if service_id:
         # confirm the service exists
         dao_fetch_service_by_id(service_id)
         rebuild_ft_data(day, service_id)
     else:
-        services = get_service_ids_that_need_billing_populated(day, day)
-        for service_id in services:
-            rebuild_ft_data(day, service_id)
+        services = get_service_ids_that_need_billing_populated(
+            get_london_midnight_in_utc(day),
+            get_london_midnight_in_utc(day + timedelta(days=1))
+        )
+        for row in services:
+            rebuild_ft_data(day, row.service_id)
 
 
 @notify_command(name='compare-ft-billing-to-monthly-billing')