rework get_fragment_count to not use ProviderStatistics

use NotficationHistory instead. Unfortunately this means the SQL
gets a bit gnarly, as we have to repeat notifications_utils'
`get_sms_fragment_count` functionality inside a SELECT 😱

app/dao/provider_statistics_dao.py

@@ -1,42 +1,51 @@
-from sqlalchemy import func
-from app.models import (ProviderStatistics, SMS_PROVIDERS, EMAIL_PROVIDERS, ProviderDetails)
+from sqlalchemy import func, cast, Float, case
+
+from app import db
+from app.models import (
+    ProviderStatistics,
+    ProviderDetails,
+    NotificationHistory,
+    SMS_TYPE,
+    EMAIL_TYPE,
+    NOTIFICATION_STATUS_TYPES_BILLABLE
+    )
 
 
 def get_provider_statistics(service, **kwargs):
-    return filter_query(ProviderStatistics.query, service, **kwargs)
-
-
-def get_fragment_count(service, date_from, date_to):
-    sms_query = filter_query(
-        ProviderStatistics.query,
-        service,
-        providers=SMS_PROVIDERS,
-        date_from=date_from,
-        date_to=date_to
-    )
-    email_query = filter_query(
-        ProviderStatistics.query,
-        service,
-        providers=EMAIL_PROVIDERS,
-        date_from=date_from,
-        date_to=date_to
-    )
-    return {
-        'sms_count': int(sms_query.with_entities(
-            func.sum(ProviderStatistics.unit_count)).scalar()) if sms_query.count() > 0 else 0,
-        'email_count': int(email_query.with_entities(
-            func.sum(ProviderStatistics.unit_count)).scalar()) if email_query.count() > 0 else 0
-    }
-
-
-def filter_query(query, service, **kwargs):
-    query = query.filter_by(service=service)
+    query = ProviderStatistics.query.filter_by(service=service)
     if 'providers' in kwargs:
         providers = ProviderDetails.query.filter(ProviderDetails.identifier.in_(kwargs['providers'])).all()
         provider_ids = [provider.id for provider in providers]
         query = query.filter(ProviderStatistics.provider_id.in_(provider_ids))
-    if 'date_from' in kwargs:
-        query.filter(ProviderStatistics.day >= kwargs['date_from'])
-    if 'date_to' in kwargs:
-        query.filter(ProviderStatistics.day <= kwargs['date_to'])
     return query
+
+
+def get_fragment_count(service_id):
+    sms_count = db.session.query(
+        func.sum(
+            case(
+                [
+                    (
+                        NotificationHistory.content_char_count <= 160,
+                        func.ceil(cast(NotificationHistory.content_char_count, Float) / 153)
+                    )
+                ],
+                else_=1
+            )
+        )
+    ).filter(
+        NotificationHistory.service_id == service_id,
+        NotificationHistory.notification_type == SMS_TYPE,
+        NotificationHistory.status.in_(NOTIFICATION_STATUS_TYPES_BILLABLE)
+    )
+    email_count = db.session.query(
+        func.count(NotificationHistory.id)
+    ).filter(
+        NotificationHistory.service_id == service_id,
+        NotificationHistory.notification_type == EMAIL_TYPE,
+        NotificationHistory.status.in_(NOTIFICATION_STATUS_TYPES_BILLABLE)
+    )
+    return {
+        'sms_count': int(sms_count.scalar() or 0),
+        'email_count': email_count.scalar() or 0
+    }