add broadcast message crud

new blueprint `/service/<id>/broadcast-message` with the following
endpoints:

* GET / - get all broadcast messages for a service
* GET /<id> - get a single broadcast message
* POST / - create a new broadcast message
* POST /<id> - update an existing broadcast message's data
* POST /<id>/status - move a broadcast message to a new status

I've kept the regular data update (eg personalisation, start and end
times) separate from the status update, just to keep separation of
concerns a bit more rigid, especially around who can update.

I've included schemas for the three POSTs, they're pretty
straightforward.

app/broadcast_message/rest.py

@@ -0,0 +1,123 @@
+from datetime import datetime
+
+import iso8601
+from flask import Blueprint, jsonify, request
+
+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.dao.broadcast_message_dao import (
+    dao_create_broadcast_message,
+    dao_get_broadcast_message_by_id_and_service_id,
+    dao_get_broadcast_messages_for_service,
+    dao_update_broadcast_message,
+)
+from app.dao.services_dao import dao_fetch_service_by_id
+from app.errors import register_errors
+from app.models import BroadcastMessage, BroadcastStatusType
+from app.broadcast_message.broadcast_message_schema import (
+    create_broadcast_message_schema,
+    update_broadcast_message_schema,
+    update_broadcast_message_status_schema,
+)
+from app.schema_validation import validate
+
+broadcast_message_blueprint = Blueprint(
+    'broadcast_message',
+    __name__,
+    url_prefix='/service/<uuid:service_id>/broadcast-message'
+)
+register_errors(broadcast_message_blueprint)
+
+
+def _parse_nullable_datetime(dt):
+    if dt:
+        return iso8601.parse_date(dt).replace(tzinfo=None)
+    return dt
+
+
+@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.
+    # we might need stuff like template name for showing on the dashboard.
+    # TODO: should this paginate or filter on dates or anything?
+    broadcast_messages = [o.serialize() for o in dao_get_broadcast_messages_for_service(service_id)]
+    return jsonify(broadcast_messages=broadcast_messages)
+
+
+@broadcast_message_blueprint.route('/<uuid:broadcast_message_id>', methods=['GET'])
+def get_broadcast_message(service_id, broadcast_message_id):
+    return jsonify(dao_get_broadcast_message_by_id_and_service_id(broadcast_message_id, service_id).serialize())
+
+
+@broadcast_message_blueprint.route('', methods=['POST'])
+def create_broadcast_message(service_id):
+    data = request.get_json()
+
+    validate(data, create_broadcast_message_schema)
+    service = dao_fetch_service_by_id(data['service_id'])
+    user = get_user_by_id(data['created_by'])
+    template = dao_get_template_by_id_and_service_id(data['template_id'], data['service_id'])
+
+    broadcast_message = BroadcastMessage(
+        service_id=service.id,
+        template_id=template.id,
+        template_version=template.version,
+        personalisation=data.get('personalisation', {}),
+        areas=data.get('areas', []),
+        status=BroadcastStatusType.DRAFT,
+        starts_at=_parse_nullable_datetime(data.get('starts_at')),
+        finishes_at=_parse_nullable_datetime(data.get('finishes_at')),
+        created_by_id=user.id,
+    )
+
+    dao_create_broadcast_message(broadcast_message)
+
+    return jsonify(broadcast_message.serialize()), 201
+
+
+@broadcast_message_blueprint.route('/<uuid:broadcast_message_id>', methods=['POST'])
+def update_broadcast_message(service_id, broadcast_message_id):
+    data = request.get_json()
+
+    validate(data, update_broadcast_message_schema)
+
+    broadcast_message = dao_get_broadcast_message_by_id_and_service_id(broadcast_message_id, service_id)
+
+    if 'personalisation' in data:
+        broadcast_message.personalisation = data['personalisation']
+    if 'starts_at' in data:
+        broadcast_message.starts_at = _parse_nullable_datetime(data['starts_at'])
+    if 'finishes_at' in data:
+        broadcast_message.starts_at = _parse_nullable_datetime(data['finishes_at'])
+    if 'areas' in data:
+        broadcast_message.areas = data['areas']
+
+    dao_update_broadcast_message(broadcast_message)
+
+    return jsonify(broadcast_message.serialize()), 200
+
+
+@broadcast_message_blueprint.route('/<uuid:broadcast_message_id>/status', methods=['POST'])
+def update_broadcast_message_status(service_id, broadcast_message_id):
+    data = request.get_json()
+
+    validate(data, update_broadcast_message_status_schema)
+    broadcast_message = dao_get_broadcast_message_by_id_and_service_id(broadcast_message_id, service_id)
+
+    new_status = data['status']
+
+    # TODO: Restrict status transitions
+    # TODO: Do we need to validate that the user belongs to the same service, isn't the creator, has permissions, etc?
+    # or is that admin's job
+    if new_status == BroadcastStatusType.BROADCASTING:
+        broadcast_message.approved_at = datetime.utcnow()
+        broadcast_message.approved_by = get_user_by_id(data['created_by'])
+    if new_status == BroadcastStatusType.CANCELLED:
+        broadcast_message.cancelled_at = datetime.utcnow()
+        broadcast_message.cancelled_by = get_user_by_id(data['created_by'])
+
+    broadcast_message.status = new_status
+
+    dao_update_broadcast_message(broadcast_message)
+
+    return jsonify(broadcast_message.serialize()), 200