DB-backed bus stalking pretty much done.

supabase/migrations/20240409190001_bus_funcs.sql

@@ -7,6 +7,7 @@ CREATE EXTENSION IF NOT EXISTS "pg_net" SCHEMA extensions;
 -- then second cron job updates from net._http_response table.
 create table if not exists raw_bus_positions (
   request_id int not null,
+  created timestamp with time zone not null default now(),
   response_status int null,
   response_json jsonb null
 );
@@ -55,12 +56,11 @@ create or replace function create_api_url(bus_routes text[]) returns text langua
 $$;
 
 create or replace function gather_bus_data()
-returns int language sql
+returns void language sql
 as $$
-  select
+  insert into raw_bus_positions (request_id) select
   net.http_get(
     url := create_api_url(array['1', '2', '3']),
     headers := '{"Content-Type": "application/json"}'::jsonb
-  )
-  as request_id;
+  );
 $$;

supabase/migrations/20240409210612_scheduled-jobs.sql

@@ -0,0 +1,40 @@
+-- downloads data async into the http response table.
+select
+  cron.schedule(
+    'download-bus-data',
+    '5 seconds',
+    $$
+    select gather_bus_data();
+    $$
+  );
+
+-- copies data into a more permanent tabe/more useful format. note:
+-- supabase has an issue where you cannot delete these triggers
+-- directly, but a cascading delete of the trigger function also
+-- removes the trigger itself.
+CREATE FUNCTION copy_to_raw_table() RETURNS trigger LANGUAGE plpgsql AS $$
+  BEGIN
+    -- NOTE: the http_response sequence resets on DB restart, so there
+    -- is potential for old responses to have duplicated ids. we use a
+    -- constraint to only update newer entries (within the last 30
+    -- seconds). this should make accidentally overwriting older data
+    -- with newer values difficult. The API also provides a
+    -- lastUpdated value. we require that raw.created is at or after
+    -- that value to be updated.
+    update raw_bus_positions raw
+       set response_json = NEW.content::jsonb,
+           response_status = NEW.status_code
+     where raw.request_id = NEW.id
+       -- fairly generous constraint to account for long requests.
+       and raw.created >= (NEW.created - '30 seconds'::interval)
+       and raw.created >= (NEW.content::jsonb->'data'->'BusLocationByRoute'->>'lastUpdate')::timestamptz
+       and raw.response_json is null;
+    RETURN NULL; -- this is an AFTER trigger
+  END;
+$$;
+
+CREATE CONSTRAINT TRIGGER copy_http_response
+  AFTER INSERT ON net._http_response
+  DEFERRABLE INITIALLY DEFERRED
+  FOR EACH ROW
+  EXECUTE FUNCTION copy_to_raw_table();