virtual_rider.js

let atStopState = (id) => "at_stop:" + id;
let onTripState = (id) => "on_trip:" + id;

let MAX_TIME = 1000 * 60;

class StateMap {
  constructor() {
    this.earliestRidersAtStates = {};
  }
  addRider(rider) {
    let existing = this.earliestRidersAtStates[rider.state];
    if (!existing || rider.time < existing.time) {
      this.earliestRidersAtStates[rider.state] = rider;
      return true;
    }
    return false;
  }
  addRiderAndTransfersByAppendingStop(oldRider, stopId, time, allTransfers) {
    let direct = oldRider.byAdding(atStopState(stopId), time);
    if (this.addRider(direct)) {
      // add all transfers:
      for (let transfer of allTransfers[stopId] || []) {
        this.addRiderAndTransfersByAppendingStop(
          direct,
          transfer["to"],
          time + transfer.time,
          allTransfers
        );
      }
    }
  }
}

class Rider {
  constructor(states, time) {
    this.states = states; // states are strings
    this.time = time;
    this.state = states.length ? states[states.length - 1] : null;
  }
  byAdding(state, finalTime) {
    return new Rider([...this.states, state], finalTime);
  }
}

let _computeTravelTimes = (
  startStationId,
  endStationIds,
  transfers,
  events,
  startTime
) => {
  let stateMap = new StateMap();

  let emptyPath = new Rider([], startTime);
  stateMap.addRiderAndTransfersByAppendingStop(
    emptyPath,
    startStationId,
    startTime,
    transfers
  );
  // console.log(stateMap);

  for (let { time, trip_id, stop_id, route_name } of events) {
    // model exiting the train:
    let riderOnTrain = stateMap.earliestRidersAtStates[onTripState(trip_id)];
    if (riderOnTrain && riderOnTrain.time <= time) {
      stateMap.addRiderAndTransfersByAppendingStop(
        riderOnTrain,
        stop_id,
        time,
        transfers
      );
    }
    // model boarding the train:
    let riderOnPlatform = stateMap.earliestRidersAtStates[atStopState(stop_id)];
    if (riderOnPlatform && riderOnPlatform.time <= time) {
      let riderOnTrain = riderOnPlatform.byAdding(onTripState(trip_id), time);
      stateMap.addRider(riderOnTrain);
    }
  }

  let travelTimes = {};
  for (let stationId of endStationIds) {
    let rider = stateMap.earliestRidersAtStates[atStopState(stationId)];
    travelTimes[stationId] = rider ? rider.time - startTime : MAX_TIME;
  }
  return travelTimes;
};

let scheduleCache = {};
let getSchedule = (name, callback) => {
  if (scheduleCache[name]) {
    callback(scheduleCache[name]);
  } else {
    d3.json("./schedules/" + name + ".json", (schedule) => {
      scheduleCache[name] = schedule;
      callback(schedule);
    });
  }
};
let computeTravelTimes = (startStationId, scheduleName, callback) => {
  getSchedule(scheduleName, (schedule) => {
    callback(
      _computeTravelTimes(
        startStationId,
        Object.keys(subway.stations),
        gtfs_transfers,
        schedule.events,
        schedule.start_time
      )
    );
  });
};

// let HOURS = 60 * 60;
// console.log(computeTravelTimes('127', Object.keys(subway.stations), 8*HOURS, gtfs_json, 'weekdays'));