Move validate_and_update_broadcast_message_status to a utils file

This is because that function is used both when broadcast status
is updated via API and via admin, so it's a shared resource.

Also move and update tests for updating broadcast message status
so things are tested at source and repetition is avoided.

app/broadcast_message/rest.py

@@ -1,7 +1,5 @@
-from datetime import datetime
-
 import iso8601
-from flask import Blueprint, current_app, jsonify, request
+from flask import Blueprint, jsonify, request
 from notifications_utils.template import BroadcastMessageTemplate
 
 from app.broadcast_message.broadcast_message_schema import (
@@ -9,8 +7,9 @@ from app.broadcast_message.broadcast_message_schema import (
     update_broadcast_message_schema,
     update_broadcast_message_status_schema,
 )
-from app.celery.broadcast_message_tasks import send_broadcast_event
-from app.config import QueueNames
+from app.broadcast_message.utils import (
+    validate_and_update_broadcast_message_status,
+)
 from app.dao.broadcast_message_dao import (
     dao_get_broadcast_message_by_id_and_service_id,
     dao_get_broadcast_messages_for_service,
@@ -20,12 +19,7 @@ from app.dao.services_dao import dao_fetch_service_by_id
 from app.dao.templates_dao import dao_get_template_by_id_and_service_id
 from app.dao.users_dao import get_user_by_id
 from app.errors import InvalidRequest, register_errors
-from app.models import (
-    BroadcastEvent,
-    BroadcastEventMessageType,
-    BroadcastMessage,
-    BroadcastStatusType,
-)
+from app.models import BroadcastMessage, BroadcastStatusType
 from app.schema_validation import validate
 
 broadcast_message_blueprint = Blueprint(
@@ -42,44 +36,6 @@ def _parse_nullable_datetime(dt):
     return dt
 
 
-def validate_and_update_broadcast_message_status(broadcast_message, new_status, updating_user):
-    if new_status not in BroadcastStatusType.ALLOWED_STATUS_TRANSITIONS[broadcast_message.status]:
-        raise InvalidRequest(
-            f'Cannot move broadcast_message {broadcast_message.id} from {broadcast_message.status} to {new_status}',
-            status_code=400
-        )
-
-    if new_status == BroadcastStatusType.BROADCASTING:
-        # training mode services can approve their own broadcasts
-        if updating_user == broadcast_message.created_by and not broadcast_message.service.restricted:
-            raise InvalidRequest(
-                f'User {updating_user.id} cannot approve their own broadcast_message {broadcast_message.id}',
-                status_code=400
-            )
-        elif len(broadcast_message.areas['simple_polygons']) == 0:
-            raise InvalidRequest(
-                f'broadcast_message {broadcast_message.id} has no selected areas and so cannot be broadcasted.',
-                status_code=400
-            )
-        else:
-            broadcast_message.approved_at = datetime.utcnow()
-            broadcast_message.approved_by = updating_user
-
-    if new_status == BroadcastStatusType.CANCELLED:
-        broadcast_message.cancelled_at = datetime.utcnow()
-        broadcast_message.cancelled_by = updating_user
-
-    current_app.logger.info(
-        f'broadcast_message {broadcast_message.id} moving from {broadcast_message.status} to {new_status}'
-    )
-    broadcast_message.status = new_status
-
-    dao_save_object(broadcast_message)
-
-    if new_status in {BroadcastStatusType.BROADCASTING, BroadcastStatusType.CANCELLED}:
-        _create_broadcast_event(broadcast_message)
-
-
 @broadcast_message_blueprint.route('', methods=['GET'])
 def get_broadcast_messages_for_service(service_id):
     # TODO: should this return template content/data in some way? or can we rely on them being cached admin side.
@@ -209,47 +165,3 @@ def update_broadcast_message_status(service_id, broadcast_message_id):
     validate_and_update_broadcast_message_status(broadcast_message, new_status, updating_user)
 
     return jsonify(broadcast_message.serialize()), 200
-
-
-def _create_broadcast_event(broadcast_message):
-    """
-    If the service is live and the broadcast message is not stubbed, creates a broadcast event, stores it in the
-    database, and triggers the task to send the CAP XML off.
-    """
-    service = broadcast_message.service
-
-    if not broadcast_message.stubbed and not service.restricted:
-        msg_types = {
-            BroadcastStatusType.BROADCASTING: BroadcastEventMessageType.ALERT,
-            BroadcastStatusType.CANCELLED: BroadcastEventMessageType.CANCEL,
-        }
-
-        event = BroadcastEvent(
-            service=service,
-            broadcast_message=broadcast_message,
-            message_type=msg_types[broadcast_message.status],
-            transmitted_content={"body": broadcast_message.content},
-            transmitted_areas=broadcast_message.areas,
-            # TODO: Probably move this somewhere more standalone too and imply that it shouldn't change. Should it
-            # include a service based identifier too? eg "flood-warnings@notifications.service.gov.uk" or similar
-            transmitted_sender='notifications.service.gov.uk',
-
-            # TODO: Should this be set to now? Or the original starts_at?
-            transmitted_starts_at=broadcast_message.starts_at,
-            transmitted_finishes_at=broadcast_message.finishes_at,
-        )
-
-        dao_save_object(event)
-
-        send_broadcast_event.apply_async(
-            kwargs={'broadcast_event_id': str(event.id)},
-            queue=QueueNames.BROADCASTS
-        )
-    elif broadcast_message.stubbed != service.restricted:
-        # It's possible for a service to create a broadcast in trial mode, and then approve it after the
-        # service is live (or vice versa). We don't think it's safe to send such broadcasts, as the service
-        # has changed since they were created. Log an error instead.
-        current_app.logger.error(
-            f'Broadcast event not created. Stubbed status of broadcast message was {broadcast_message.stubbed}'
-            f' but service was {"in trial mode" if service.restricted else "live"}'
-        )