Change get_providers endpoint to return no of SMS sent by each provider

In addition to the existing provider data, we also want return the number of
billable units (muliplied by the rate multiplier) that each SMS provider sent
this month. This will be used on the platform admin providers page.

Since we can no longer get all the information we need from the provider details
schema, this makes a new DAO function to get all the data for the endpoint.

app/dao/provider_details_dao.py

@@ -1,6 +1,7 @@
 from datetime import datetime
 
-from sqlalchemy import asc, desc
+from notifications_utils.timezones import convert_utc_to_bst
+from sqlalchemy import asc, desc, func
 
 from app.dao.dao_utils import transactional
 from app.provider_details.switch_providers import (
@@ -8,14 +9,10 @@ from app.provider_details.switch_providers import (
     provider_is_primary,
     switch_providers
 )
-from app.models import ProviderDetails, ProviderDetailsHistory
+from app.models import FactBilling, ProviderDetails, ProviderDetailsHistory, SMS_TYPE, User
 from app import db
 
 
-def get_provider_details():
-    return ProviderDetails.query.order_by(asc(ProviderDetails.priority), asc(ProviderDetails.notification_type)).all()
-
-
 def get_provider_details_by_id(provider_details_id):
     return ProviderDetails.query.get(provider_details_id)
 
@@ -110,3 +107,42 @@ def dao_get_sms_provider_with_equal_priority(identifier, priority):
     ).first()
 
     return provider
+
+
+def dao_get_provider_stats():
+    # this query does not include the current day since the task to populate ft_billing runs overnight
+
+    current_bst_datetime = convert_utc_to_bst(datetime.utcnow())
+    first_day_of_the_month = current_bst_datetime.date().replace(day=1)
+
+    subquery = db.session.query(
+        FactBilling.provider,
+        func.sum(FactBilling.billable_units * FactBilling.rate_multiplier).label('current_month_billable_sms')
+    ).filter(
+        FactBilling.notification_type == SMS_TYPE,
+        FactBilling.bst_date >= first_day_of_the_month
+    ).group_by(
+        FactBilling.provider
+    ).subquery()
+
+    result = db.session.query(
+        ProviderDetails.id,
+        ProviderDetails.display_name,
+        ProviderDetails.identifier,
+        ProviderDetails.priority,
+        ProviderDetails.notification_type,
+        ProviderDetails.active,
+        ProviderDetails.updated_at,
+        ProviderDetails.supports_international,
+        User.name.label('created_by_name'),
+        func.coalesce(subquery.c.current_month_billable_sms, 0).label('current_month_billable_sms')
+    ).outerjoin(
+        subquery, ProviderDetails.identifier == subquery.c.provider
+    ).outerjoin(
+        User, ProviderDetails.created_by_id == User.id
+    ).order_by(
+        ProviderDetails.notification_type,
+        ProviderDetails.priority,
+    ).all()
+
+    return result