One row per bus position entry. TimescaleDB!

README.md

@@ -0,0 +1,25 @@
+# Jokullbase
+
+How to track how late buses are:
+ - [ ] Download bus route data
+ - [ ] Insert raw bus positions into timescaledb/postGIS table?
+   - [ ] "Fan-out" JSON responses into one DB row per datapoint.
+ - [ ] Download routes.
+   - There is an endpoint called Timetable, which takes a route number
+     (along with day of week etc).
+   - The timetable response includes a list of stops in the route,
+     along with the route ID.
+   - There is an endpoint called **BusLocationByStop**, which takes a
+     stop ID as a parameter.
+	 - This information has upcoming arrivals, included estimated
+       arrival time, along with the current position of the bus.
+   - Record stop info every few minutes, notably the arrivals.
+ - [ ] Analyze actual arrival vs what the stop endpoint said about the
+       arrival.
+   - Use PostGIS to compute "bus arrived" event: When bus is within X
+     meters of a stop on its route, mark that as an arrival event.
+   - Once we have bus arrival events, we can compare them to arrivals
+     throughout the day.
+   - We can then discard the raw bus position data, as it's not needed
+     to store it: delete every raw data point between the last arrival
+     and the newly computed one.

supabase/migrations/20240409190001_initial.sql

@@ -2,13 +2,31 @@
 CREATE EXTENSION IF NOT EXISTS "plv8" SCHEMA pg_catalog;
 CREATE EXTENSION IF NOT EXISTS "pg_cron" SCHEMA pg_catalog;
 CREATE EXTENSION IF NOT EXISTS "pg_net" SCHEMA extensions;
+CREATE EXTENSION IF NOT EXISTS timescaledb CASCADE;
 
--- request ID is inserted by first cron job, then a trigger handles
--- insertion of response.
 CREATE TABLE IF NOT EXISTS raw_bus_positions (
   id BIGINT GENERATED ALWAYS AS IDENTITY,
-  request_id INT NOT NULL,
-  created TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
+  measured_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
   response_status INT NULL,
-  response_json JSONB NULL
+  bus_id text,
+  trip_id text,
+  route_number text,
+  headsign text,
+  tag text,
+  direction int,
+  lat decimal,
+  lon decimal
+);
+
+-- TimescaleDB Hypertable creation
+SELECT create_hypertable('raw_bus_positions', 'measured_at', chunk_time_interval => INTERVAL '10 minutes');
+CREATE INDEX bus_position_measures ON raw_bus_positions (bus_id, measured_at DESC);
+
+SELECT
+  cron.schedule(
+    'drop-old-chunks',
+    '*/10 * * * *',
+    $$
+    SELECT drop_chunks('raw_bus_positions', INTERVAL '24 hours');
+    $$
 );

supabase/migrations/20240409210612_bus_funcs.sql

@@ -46,10 +46,15 @@ $$;
 
 -- Called by a scheduled job to request data on a timer. A trigger
 -- handles insertion of the response after record initially inserted.
+CREATE TABLE IF NOT EXISTS raw_bus_position_requests(
+  request_id int,
+  created TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW()
+);
+
 CREATE OR REPLACE FUNCTION gather_bus_data()
 RETURNS void LANGUAGE sql
 as $$
-  INSERT INTO raw_bus_positions (request_id) SELECT
+  INSERT INTO raw_bus_position_requests (request_id) SELECT
   net.http_get(
     url := build_api_url(array['1', '2', '3']),
     headers := '{"Content-Type": "application/json"}'::jsonb

supabase/migrations/20240410070316_scheduled-jobs.sql

@@ -21,16 +21,36 @@ CREATE FUNCTION copy_to_raw_table() RETURNS trigger LANGUAGE plpgsql AS $$
     -- 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->'data'->'BusLocationByRoute',
-           response_status = NEW.status_code
-     WHERE raw.request_id = NEW.id
+    WITH mapped_response_rows as (
+      select x.*
+	from jsonb_to_recordset(NEW.content::jsonb->'data'->'BusLocationByRoute'->'results') x (
+	       "busId" text,
+	       "tripId" text,
+	       "routeNr" text,
+	       headsign text,
+	       tag text,
+	       direction int,
+	       lat decimal,
+	       lng decimal
+	     )
+    )
+    INSERT INTO raw_bus_positions
+	-- This needs to be in the same order as the jsonb_to_recordset call to work properly.
+	(response_status, measured_at, bus_id, trip_id, route_number, headsign, tag, direction, lat, lon)
+      SELECT
+	NEW.status_code,
+	(NEW.content::jsonb->'data'->'BusLocationByRoute'->>'lastUpdate')::timestamptz,
+	mr.*
+      FROM mapped_response_rows mr
+      JOIN raw_bus_position_requests raw_request ON raw_request.request_id = NEW.id
+    WHERE
        -- fairly generous constraint to account for long requests.
-       AND raw.created >= (NEW.created - '30 seconds'::interval)
+       raw_request.created >= (NEW.created - '30 seconds'::interval)
        -- the response must be at or after we actually sent the request.
-       AND raw.created >= (NEW.content::jsonb->'data'->'BusLocationByRoute'->>'lastUpdate')::timestamptz
-       AND NEW.status_code = 200
-       AND raw.response_json IS NULL;
+       AND raw_request.created >= (NEW.content::jsonb->'data'->'BusLocationByRoute'->>'lastUpdate')::timestamptz
+       AND NEW.status_code = 200;
+
+    DELETE FROM raw_bus_position_requests where request_id = NEW.id;
 
       -- what if we want to stream other data? we can do multiple updates in
       -- different tables, where the request id is.