jokull/README.md

# Jokullbase

How to track how late buses are:
 - [x] Download bus route data
 - [x] Insert raw bus positions into timescaledb/postGIS table?
   - [x] "Fan-out" JSON responses into one DB row per datapoint.
 - [ ] Download routes/stops.
   - There is an endpoint called Stops.
   - 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.
   - This will be annoying to do only in DB since we have a trigger
     for bus positions.
 - [ ] 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.

Arrival computation:
 - Can use edge functions for this?
 - Function takes a bus route number, start time, end time.
 - Cron in DB calls the edge functions, using state as function inputs.
   - state = last interval end time, so we can properly calculate time interval to check.
   - or rather use last ID in the raw table, so we don't skip entries.
 - Query DB to get raw bus positions in the interval.
 - Query DB to get all stops on the route (during the interval? some stops not in use sometimes)
 - For each bus ID, find the raw position where its lat,lon are X meters away from stop lat,lons.
 - These are arrival times for this bus ID, at each stop.
 - Insert into arrivals.
 - After all arrivals computed, drop all raw positions for this bus from DB.

Useful stuff:

```
SELECT buses_at_stops.* FROM (SELECT DISTINCT ON (s.id, h.measured_at) s.id, s.stop_name, ST_AsText(s.coords) as stop_coords, h.measured_at, h.bus_id, ST_AsText(h.coords) as bus_coords, ST_Distance(s.coords, h.coords) as distance
  FROM bus_stops s
    JOIN raw_bus_positions h ON ST_DWithin(s.coords, h.coords, 30)) AS buses_at_stops
    WHERE buses_at_stops.bus_id like '1%'
    ORDER BY buses_at_stops.measured_at desc;
```