Add endpoint for breakdown of activity by month

This endpoint will eventualy replace the weekly breakdown one. By month
for a given financial year is better, because it gives us consistency
with the breakdown of financial usage (and eventually consistency with
the template usage).

The code to do this is a bit convoluted, in order to fill out the counts
for months and statuses where we don’t have notifications.

This will make the admin side of this easier, because we can rely on
there always being numbers available. The admin side will deal with
summing the statuses (eg `temporary-failure` > `failed`) because this
is presentational.

This commit also modifies the usage count to use `.between()` for
consistency.

app/service/rest.py

@@ -30,7 +30,9 @@ from app.dao.services_dao import (
     dao_archive_service,
     fetch_stats_by_date_range_for_all_services,
     dao_suspend_service,
-    dao_resume_service)
+    dao_resume_service,
+    dao_fetch_monthly_historical_stats_for_service,
+)
 from app.dao.service_whitelist_dao import (
     dao_fetch_service_whitelist,
     dao_add_and_commit_whitelisted_contacts,
@@ -273,6 +275,18 @@ def get_weekly_notification_stats(service_id):
     return jsonify(data={week.date().isoformat(): statistics for week, statistics in stats.items()})
 
 
+@service_blueprint.route('/<uuid:service_id>/notifications/monthly', methods=['GET'])
+def get_monthly_notification_stats(service_id):
+    service = dao_fetch_service_by_id(service_id)
+    try:
+        return jsonify(data=dao_fetch_monthly_historical_stats_for_service(
+            service.id,
+            int(request.args.get('year', 'NaN'))
+        ))
+    except ValueError:
+        raise InvalidRequest('Year must be a number', status_code=400)
+
+
 def get_detailed_service(service_id, today_only=False):
     service = dao_fetch_service_by_id(service_id)
     stats_fn = dao_fetch_todays_stats_for_service if today_only else dao_fetch_stats_for_service