parse datetimes from mmg inbound sms

the DateRecieved field from MMG comes in with +s instead of spaces,
and uriencoded (the same as how they format their messages)
Make sure we decode this, and then convert to a UTC timestamp

app/notifications/receive_notifications.py

@@ -1,7 +1,7 @@
 from urllib.parse import unquote
-from flask import jsonify
 
-from flask import Blueprint, current_app, request
+import iso8601
+from flask import jsonify, Blueprint, current_app, request
 from notifications_utils.recipients import normalise_phone_number
 
 from app import statsd_client
@@ -9,6 +9,7 @@ from app.dao.services_dao import dao_fetch_services_by_sms_sender
 from app.dao.inbound_sms_dao import dao_create_inbound_sms
 from app.models import InboundSms
 from app.errors import register_errors
+from app.utils import convert_bst_to_utc
 
 receive_notifications_blueprint = Blueprint('receive_notifications', __name__)
 register_errors(receive_notifications_blueprint)
@@ -48,18 +49,33 @@ def receive_mmg_sms():
     return 'RECEIVED', 200
 
 
-def format_message(message):
+def format_mmg_message(message):
     return unquote(message.replace('+', ' '))
 
 
+def format_mmg_datetime(date):
+    """
+    We expect datetimes in format 2017-05-21+11%3A56%3A11 - ie, spaces replaced with pluses, and URI encoded
+    (the same as UTC)
+    """
+    orig_date = format_mmg_message(date)
+    parsed_datetime = iso8601.parse_date(orig_date).replace(tzinfo=None)
+    return convert_bst_to_utc(parsed_datetime)
+
+
 def create_inbound_mmg_sms_object(service, json):
-    message = format_message(json['Message'])
+    message = format_mmg_message(json['Message'])
     user_number = normalise_phone_number(json['MSISDN'])
+
+    provider_date = json.get('DateRecieved')
+    if provider_date:
+        provider_date = format_mmg_datetime(provider_date)
+
     inbound = InboundSms(
         service=service,
         notify_number=service.sms_sender,
         user_number=user_number,
-        provider_date=json.get('DateRecieved'),
+        provider_date=provider_date,
         provider_reference=json.get('ID'),
         content=message,
     )