create new stats endpoint

the admin app currently calls get_detailed_service, which gets
notification stats, adds them on to the rest of the detailed service
endpoint, and returns them. However, the admin app then only looks at
the stats - it doesn't look at the rest of the service object.

This is called in a few high profile places - the dashboard, the
notification summary page, and when you send a job. By creating a
separate endpoint that ignores the rest of the service object (and no
marshmallow too!), the hope is that we'll improve some slowness we've
been seeing.

Note: The old detailed function will still need to stay - it's used
by get_services(detailed=True) for the platform admin page.

app/service/rest.py

@@ -170,6 +170,11 @@ def get_service_by_id(service_id):
     return jsonify(data=data)
 
 
+@service_blueprint.route('/<uuid:service_id>/statistics')
+def get_service_notification_statistics(service_id):
+    return jsonify(data=get_service_statistics(service_id, request.args.get('today_only') == 'True'))
+
+
 @service_blueprint.route('', methods=['POST'])
 def create_service():
     data = request.get_json()
@@ -411,12 +416,16 @@ def get_monthly_notification_stats(service_id):
 
 def get_detailed_service(service_id, today_only=False):
     service = dao_fetch_service_by_id(service_id)
+
+    service.statistics = get_service_statistics(service_id, today_only)
+    return detailed_service_schema.dump(service).data
+
+
+def get_service_statistics(service_id, today_only):
+    # today_only flag is used by the send page to work out if the service will exceed their daily usage by sending a job
     stats_fn = dao_fetch_todays_stats_for_service if today_only else dao_fetch_stats_for_service
     stats = stats_fn(service_id)
-
-    service.statistics = statistics.format_statistics(stats)
-
-    return detailed_service_schema.dump(service).data
+    return statistics.format_statistics(stats)
 
 
 def get_detailed_services(start_date, end_date, only_active=False, include_from_test_key=True):

tests/app/service/test_rest.py

@@ -3085,3 +3085,35 @@ def test_get_platform_stats_creates_zero_stats(client, notify_db_session):
     assert json_resp['email'] == {'failed': 1, 'requested': 2, 'delivered': 1}
     assert json_resp['letter'] == {'failed': 0, 'requested': 0, 'delivered': 0}
     assert json_resp['sms'] == {'failed': 0, 'requested': 4, 'delivered': 3}
+
+
+@pytest.mark.parametrize('today_only, stats', [
+    (False, {'requested': 2, 'delivered': 1, 'failed': 0}),
+    (True, {'requested': 1, 'delivered': 0, 'failed': 0})
+], ids=['seven_days', 'today'])
+def test_get_service_notification_statistics(admin_request, sample_template, today_only, stats):
+    with freeze_time('2000-01-01T12:00:00'):
+        create_notification(sample_template, status='delivered')
+    with freeze_time('2000-01-02T12:00:00'):
+        create_notification(sample_template, status='created')
+        resp = admin_request.get(
+            'service.get_service_notification_statistics',
+            service_id=sample_template.service_id,
+            today_only=today_only
+        )
+
+    assert set(resp['data'].keys()) == {SMS_TYPE, EMAIL_TYPE, LETTER_TYPE}
+    assert resp['data'][SMS_TYPE] == stats
+
+
+def test_get_service_notification_statistics_with_unknown_service(admin_request):
+    resp = admin_request.get(
+        'service.get_service_notification_statistics',
+        service_id=uuid.uuid4()
+    )
+
+    assert resp['data'] == {
+        SMS_TYPE: {'requested': 0, 'delivered': 0, 'failed': 0},
+        EMAIL_TYPE: {'requested': 0, 'delivered': 0, 'failed': 0},
+        LETTER_TYPE: {'requested': 0, 'delivered': 0, 'failed': 0},
+    }