jokull/supabase/migrations/20240409190001_initial.sql

-- extensions
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;
CREATE EXTENSION IF NOT EXISTS postgis;

-- Raw bus positions time series table.
CREATE TABLE IF NOT EXISTS raw_bus_positions (
  id BIGINT GENERATED ALWAYS AS IDENTITY,
  measured_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
  response_status INT NULL,
  bus_id text,
  trip_id text,
  route_number text,
  headsign text,
  tag text,
  direction int,
  coords geography(Point, 4326)
);

COMMENT ON TABLE raw_bus_positions IS 'Recordings of bus positions. Mostly transient data.';
COMMENT ON COLUMN raw_bus_positions.coords IS 'GPS coords of bus. PostGIS Point.';

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);
CREATE INDEX raw_bus_positions_spatial ON raw_bus_positions USING GIST (coords);

SELECT
  cron.schedule(
    'drop-old-chunks',
    '*/10 * * * *',
    $$
    SELECT drop_chunks('raw_bus_positions', INTERVAL '24 hours');
    $$
);

-- Record of all bus stops.
create table bus_stops(
  id BIGINT PRIMARY KEY,
  stop_name TEXT,
  coords geography(Point, 4326),
  "type" INT,
  rotation INT,
  code TEXT,
  is_terminal BOOL,
  routes TEXT[]
);

CREATE INDEX bus_stops_spatial ON bus_stops USING GIST (coords);

-- Bus Position Related Functions
-- encode straeto API params into the query string by the graphql API.
-- yes, javascript in the database: the lazy way.
CREATE OR REPLACE FUNCTION encode_straeto_querystring(obj jsonb) RETURNS text
LANGUAGE plv8 STRICT IMMUTABLE AS $$
  return Object.keys(obj).map(function(variableName) {
    const variableValue = obj[variableName];
    if (typeof variableValue == 'object') {
      return encodeURIComponent(variableName) + '=' + encodeURIComponent(JSON.stringify(variableValue));
    } else {
      return encodeURIComponent(variableName) + '=' + encodeURIComponent(variableValue);
    }
  }).join('&');
$$;

CREATE OR REPLACE FUNCTION create_straeto_parameters(bus_routes text[]) RETURNS jsonb
LANGUAGE plpgsql AS $$
  DECLARE query_params jsonb;
  BEGIN
    -- This is the unencoded GraphQL request payload.
    query_params := '{
      "operationName": "BusLocationByRoute",
      "variables": { "trips":[], "routes": [] },
      "extensions": {
        "persistedQuery": {
          "version": 1,
          "sha256Hash": "8f9ee84171961f8a3b9a9d1a7b2a7ac49e7e122e1ba1727e75cfe3a94ff3edb8"
        }
      }
    }'::jsonb;

    -- Add requested bus routes to the `routes` GraphQL variable.
    SELECT INTO query_params
		jsonb_set(query_params, '{variables, routes}', array_to_json(bus_routes)::jsonb);
    RETURN query_params;
  END
$$;

-- Builds the full request URL to download bus positions of the given
-- route numbers.
CREATE OR REPLACE FUNCTION build_api_url(bus_routes text[]) RETURNS text LANGUAGE sql AS $$
  SELECT concat(
    'https://straeto.is/graphql?',
    encode_straeto_querystring(create_straeto_parameters(bus_routes))
  );
$$;

-- 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 $$
  INSERT INTO raw_bus_position_requests (request_id) SELECT
  net.http_get(
    url := build_api_url(array['1', '2', '3']),
    headers := '{"Content-Type": "application/json"}'::jsonb
  );
$$;

-- Configuration of streaming bus positions into Postgres
-- 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: in
-- supabase, you cannot delete triggers on net._http_response
-- 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.
    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
	(response_status, measured_at, bus_id, trip_id, route_number, headsign, tag, direction, coords)
      SELECT
	NEW.status_code,
	(NEW.content::jsonb->'data'->'BusLocationByRoute'->>'lastUpdate')::timestamptz,
	mr."busId", mr."tripId", mr."routeNr", mr.headsign, mr.tag, mr.direction,
	ST_SetSRID(ST_MakePoint(mr.lat, mr.lng), 4326) -- PostGIS coordinates
      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.
       raw_request.created >= (NEW.created - '30 seconds'::interval)
       -- the response must be at or after we actually sent the request.
       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.
    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();


-- Create a trigger on insert into raw_bus_positions. It runs a
-- spatial query against bus stops and finds out if this measurement
-- is within X meters of a bus stop. If so, queue up to sanity check
-- pipeline. Otherwise, delete from table.
CREATE TABLE potential_arrivals(
  id BIGINT GENERATED ALWAYS AS IDENTITY,
  raw_pos_id BIGINT NOT NULL,
  bus_id text NOT NULL,
  bus_coords GEOGRAPHY(Point, 4326) NOT NULL,
  measured_at TIMESTAMP WITH TIME ZONE NOT NULL,
  stop_id bigint NOT NULL,
  distance decimal NOT NULL
);

SELECT create_hypertable('potential_arrivals', 'measured_at', chunk_time_interval => INTERVAL '10 minutes');

CREATE INDEX potential_arrives_raw_pos_id ON potential_arrivals (raw_pos_id);
CREATE INDEX potential_arrivals_measures ON potential_arrivals (bus_id, measured_at DESC);
CREATE INDEX potential_arrivals_spatial ON potential_arrivals USING GIST (bus_coords);

CREATE FUNCTION check_near_stop() RETURNS trigger LANGUAGE plpgsql AS $$
  BEGIN
    INSERT INTO potential_arrivals (raw_pos_id, bus_id, bus_coords, measured_at, stop_id, distance)
    SELECT DISTINCT ON (pos.id)
      pos.id,
      pos.bus_id,
      pos.coords,
      pos.measured_at,
      stops.id,
      ST_Distance(pos.coords, stops.coords) as distance
      FROM raw_bus_positions pos
	   join bus_stops stops on ST_DWithin(pos.coords, stops.coords, 30)
     WHERE pos.id = NEW.id;

    -- Remove any raw positions that are not potentially a bus
    -- stopping at a bus stop.
    DELETE FROM raw_bus_positions pos
     WHERE pos.id = NEW.id and pos.id not in (select raw_pos_id from potential_arrivals);

    RETURN NULL; -- this is an AFTER trigger
  END;
$$;

CREATE CONSTRAINT TRIGGER add_potential_stop
  AFTER INSERT ON raw_bus_positions
  DEFERRABLE INITIALLY DEFERRED
  FOR EACH ROW
  EXECUTE FUNCTION check_near_stop();