Added Scheduled task to get stats for template usage

Currently some pages are timing out due to the time it takes to perform
database queries. This is an attempt to improve the performance by
performing the query against the notification history table once a day
and use the notification table for a delta between midnight and the when
the page is run and combine the results.

- Added Celery task for doing the work
- Added a dao to handle the insert and update of the stats table
- Updated tests to test the new functionality

tests/app/celery/test_scheduled_tasks.py

@@ -2,11 +2,13 @@ from datetime import datetime, timedelta
 from functools import partial
 from unittest.mock import call, patch, PropertyMock
 
+import functools
 from flask import current_app
 
 import pytest
 from freezegun import freeze_time
 
+from app import db
 from app.celery import scheduled_tasks
 from app.celery.scheduled_tasks import (
     check_job_status,
@@ -30,8 +32,8 @@ from app.celery.scheduled_tasks import (
     send_total_sent_notifications_to_performance_platform,
     switch_current_sms_provider_on_slow_delivery,
     timeout_job_statistics,
-    timeout_notifications
-)
+    timeout_notifications,
+    daily_stats_template_usage_my_month)
 from app.clients.performance_platform.performance_platform_client import PerformancePlatformClient
 from app.config import QueueNames, TaskNames
 from app.dao.jobs_dao import dao_get_job_by_id
@@ -49,19 +51,24 @@ from app.models import (
     NOTIFICATION_PENDING,
     NOTIFICATION_CREATED,
     KEY_TYPE_TEST,
-    MonthlyBilling
-)
+    MonthlyBilling,
+    StatsTemplateUsageByMonth)
 from app.utils import get_london_midnight_in_utc
 from app.v2.errors import JobIncompleteError
 from tests.app.db import create_notification, create_service, create_template, create_job, create_rate
 from tests.app.conftest import (
     sample_job as create_sample_job,
-    sample_notification_history as create_notification_history,
     create_custom_template,
     datetime_in_past
 )
 from tests.app.aws.test_s3 import single_s3_object_stub
-from tests.conftest import set_config_values
+from tests.conftest import set_config_values, notify_db, notify_db_session
+
+from tests.app.conftest import (
+    sample_notification as create_notification,
+    sample_notification_history as create_notification_history,
+    sample_template as create_sample_template
+)
 
 
 def _create_slow_delivery_notification(provider='mmg'):
@@ -834,3 +841,108 @@ def test_check_job_status_task_raises_job_incomplete_error_for_multiple_jobs(moc
         args=([str(job.id), str(job_2.id)],),
         queue=QueueNames.JOBS
     )
+
+
+def test_daily_stats_template_usage_my_month(notify_db, notify_db_session):
+    notification_history = functools.partial(
+        create_notification_history,
+        notify_db,
+        notify_db_session,
+        status='delivered'
+    )
+
+    template_one = create_sample_template(notify_db, notify_db_session)
+    template_two = create_sample_template(notify_db, notify_db_session)
+
+    notification_history(created_at=datetime(2017, 10, 1), sample_template=template_one)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime.now(), sample_template=template_two)
+
+    daily_stats_template_usage_my_month()
+
+    results = db.session.query(StatsTemplateUsageByMonth).all()
+
+    assert len(results) == 2
+
+    for result in results:
+        if result.template_id == template_one.id:
+            assert result.template_id == template_one.id
+            assert result.month == 10
+            assert result.year == 2017
+            assert result.count == 1
+        elif result.template_id == template_two.id:
+            assert result.template_id == template_two.id
+            assert result.month == 4
+            assert result.year == 2016
+            assert result.count == 2
+        else:
+            raise AssertionError()
+
+
+def test_daily_stats_template_usage_my_month_no_data():
+    daily_stats_template_usage_my_month()
+
+    results = db.session.query(StatsTemplateUsageByMonth).all()
+
+    assert len(results) == 0
+
+
+def test_daily_stats_template_usage_my_month_multiple_runs(notify_db, notify_db_session):
+    notification_history = functools.partial(
+        create_notification_history,
+        notify_db,
+        notify_db_session,
+        status='delivered'
+    )
+
+    template_one = create_sample_template(notify_db, notify_db_session)
+    template_two = create_sample_template(notify_db, notify_db_session)
+
+    notification_history(created_at=datetime(2017, 10, 1), sample_template=template_one)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime.now(), sample_template=template_two)
+
+    daily_stats_template_usage_my_month()
+
+    template_three = create_sample_template(notify_db, notify_db_session)
+
+    notification_history(created_at=datetime(2017, 10, 1), sample_template=template_three)
+    notification_history(created_at=datetime(2017, 9, 1), sample_template=template_three)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime(2016, 4, 1), sample_template=template_two)
+    notification_history(created_at=datetime.now(), sample_template=template_two)
+
+    daily_stats_template_usage_my_month()
+
+    results = db.session.query(StatsTemplateUsageByMonth).all()
+
+    assert len(results) == 4
+
+    for result in results:
+        if result.template_id == template_one.id:
+            assert result.template_id == template_one.id
+            assert result.month == 10
+            assert result.year == 2017
+            assert result.count == 1
+        elif result.template_id == template_two.id:
+            assert result.template_id == template_two.id
+            assert result.month == 4
+            assert result.year == 2016
+            assert result.count == 4
+        elif result.template_id == template_three.id:
+            if result.month == 10:
+                assert result.template_id == template_three.id
+                assert result.month == 10
+                assert result.year == 2017
+                assert result.count == 1
+            elif result.month == 9:
+                assert result.template_id == template_three.id
+                assert result.month == 9
+                assert result.year == 2017
+                assert result.count == 1
+            else:
+                raise AssertionError()
+        else:
+            raise AssertionError()