It is not of the form
[[lat, long][lat, long]] as this would only hold a single polygon. It
instead needs to handle multiple polygons so instead is of the form
[[[lat, long][lat, long]]].
use the new endpoint from cbc proxy. create a new task that just
serializes the event and sends it across rather than sending a template
and the broadcast message.
some changes to serialize to make it json friendly etc. it also expects
sent_at and transmitted_finishes_at to always be set (we set them in the
code but don't enforce it n the DB right now), as they're required by
utils template. not sure whether we'll update db constraints to be more
strict or utils template to be more permissive just yet, wait until we
find out more about the requirements of the CBCs we integrate with.
task takes a brodcast_message_id, and makes a post to the cbc-proxy
for now, hardcode the url to the notify stub. the stub requires template
as the admin/api get it, so use the marshmallow schema to json dump it.
Note - this also required us to tweak the BroadcastMessage.serialize
function so that it converts uuids in to ids - flask's jsonify function
does that for free but requests.post doesn't sadly.
if the request fails (either 4xx or 5xx) just raise an exception and let
it bubble up for now - in the future we'll add retry logic
