tracktracker/src/tam/simulation.js

const axios = require('axios');
const turf = require('@turf/turf');
const network = require('./network.json');

const server = 'http://localhost:4321';

class Course
{
    constructor(data)
    {
        this.id = data.id;
        this.passings = {};
        this.state = null;

        // Attributes for the `stopped` state
        this.currentStop = null;

        // Attributes for the `moving` state
        this.departureStop = null;
        this.arrivalStop = null;
        this.arrivalTime = 0;
        this.traveledDistance = 0;
        this.speed = 0;

        this.position = [0, 0];
        this.angle = 0;

        this.history = [];
    }

    get currentSegment()
    {
        if (this.state !== 'moving')
        {
            return undefined;
        }

        return network.segments[`${this.departureStop}-${this.arrivalStop}`];
    }

    updateData(data)
    {
        this.line = data.line;
        this.finalStop = data.finalStop;
        Object.assign(this.passings, data.nextPassings);

        const now = Date.now();

        // Make sure we’re on the right `stopped`/`moving` state
        if (this.state === null)
        {
            let previousStop = null;
            let departureTime = 0;

            let nextStop = null;
            let arrivalTime = Infinity;

            for (let [stopId, time] of Object.entries(this.passings))
            {
                if (time > now && time < arrivalTime)
                {
                    nextStop = stopId;
                    arrivalTime = time;
                }

                if (time < now && time > departureTime)
                {
                    previousStop = stopId;
                    departureTime = time;
                }
            }

            if (nextStop === null)
            {
                return false;
            }

            if (previousStop === null)
            {
                // Teleport to the first known stop
                this.arriveToStop(nextStop);
            }
            else
            {
                // Teleport to the first known segment
                this.arriveToStop(previousStop);
                this.moveToStop(nextStop, arrivalTime);
            }
        }
        else if (this.state === 'moving')
        {
            // Should already be at the next stop
            if (this.passings[this.arrivalStop] <= now)
            {
                this.arriveToStop(this.arrivalStop);
            }
            // On the right track, update the arrival time
            else
            {
                this.arrivalTime = this.passings[this.arrivalStop];
            }
        }
        else // this.state === 'stopped'
        {
            // Try moving to the next stop
            let nextStop = null;
            let arrivalTime = Infinity;

            for (let [stopId, time] of Object.entries(this.passings))
            {
                if (time > now && time < arrivalTime)
                {
                    nextStop = stopId;
                    arrivalTime = time;
                }
            }

            if (nextStop === null)
            {
                // This course is finished
                return false;
            }

            if (nextStop !== this.currentStop)
            {
                this.moveToStop(nextStop, arrivalTime);
            }
        }

        if (this.state === 'moving')
        {
            this.speed = this.computeTheoreticalSpeed();
        }

        return true;
    }

    tick(time)
    {
        if (this.state === null)
        {
            // Ignore uninitalized courses
        }
        else if (this.state === 'moving')
        {
            // Integrate current speed in travelled distance
            const delta = this.speed * time;

            const segment = this.currentSegment;
            const length = segment.points[segment.points.length - 1].distance;
            this.traveledDistance += delta;

            if (this.traveledDistance >= length)
            {
                this.arriveToStop(this.arrivalStop);
                return;
            }

            // Recompute updated position
            const departureStop = network.stops[this.departureStop];
            const arrivalStop = network.stops[this.arrivalStop];
            const nextNodeIndex = segment.points.findIndex(
                ({distance}) => distance >= this.traveledDistance);

            if (nextNodeIndex === 0)
            {
                this.position = turf.toMercator([
                    departureStop.lon,
                    departureStop.lat
                ]);
            }
            else
            {
                const previousNode = segment.points[nextNodeIndex - 1];
                const nextNode = segment.points[nextNodeIndex];

                const previousPoint = turf.toMercator([
                    previousNode.lon,
                    previousNode.lat
                ]);

                const nextPoint = turf.toMercator([
                    nextNode.lon,
                    nextNode.lat
                ]);

                const curLength = this.traveledDistance
                    - previousNode.distance;
                const totalLength = nextNode.distance
                    - previousNode.distance;
                const t = curLength / totalLength;

                this.position = [
                    t * nextPoint[0] + (1 - t) * previousPoint[0],
                    t * nextPoint[1] + (1 - t) * previousPoint[1],
                ];

                this.angle = Math.atan2(
                    previousPoint[1] - nextPoint[1],
                    nextPoint[0] - previousPoint[0],
                );
            }
        }
        else // this.state === 'stopped'
        {
            const currentNode = network.stops[this.currentStop];

            this.position = turf.toMercator([
                currentNode.lon,
                currentNode.lat
            ]);
        }
    }

    /**
     * Transition this course to a state where it has arrived to a stop.
     *
     * @param stop Identifier for the stop to which the course arrives.
     */
    arriveToStop(stop)
    {
        this.state = 'stopped';
        this.currentStop = stop;
        this.position = turf.toMercator([
            network.stops[this.currentStop].lon,
            network.stops[this.currentStop].lat,
        ]);
        this.history.push(['arriveToStop', stop]);
    }

    /**
     * Transition this course to a state where it is moving to a stop.
     *
     * @param stop Next stop for this course.
     * @param arrivalTime Planned arrival time to that stop.
     */
    moveToStop(stop, arrivalTime)
    {
        if (!(`${this.currentStop}-${stop}` in network.segments))
        {
            console.warn(`Course ${this.id} is cannot go from stop
${this.currentStop} to stop ${stop}. Teleporting to ${stop}`);
            this.arriveToStop(stop);
            return;
        }

        this.state = 'moving';
        this.departureStop = this.currentStop;
        this.arrivalStop = stop;
        this.arrivalTime = arrivalTime;
        this.traveledDistance = 0;
        this.speed = 0;
        this.position = turf.toMercator([
            network.stops[this.departureStop].lon,
            network.stops[this.departureStop].lat,
        ]);
        this.history.push(['moveToStop', stop, arrivalTime]);

        console.info(`Course ${this.id} leaving stop ${this.currentStop} \
with initial speed ${this.computeTheoreticalSpeed() * 3600} km/h`);
    }

    /**
     * Compute the speed that needs to be maintained to arrive on time.
     */
    computeTheoreticalSpeed()
    {
        if (this.state !== 'moving')
        {
            return 0;
        }

        const segment = this.currentSegment;
        const length = segment.points[segment.points.length - 1].distance;

        const remainingTime = this.arrivalTime - Date.now();
        const remainingDistance = length - this.traveledDistance;

        if (remainingDistance <= 0)
        {
            return 0;
        }
        else if (remainingTime <= 0)
        {
            // We’re late, go to maximum speed
            return 50 / 3600; // 50 km/h
        }
        else
        {
            return remainingDistance / remainingTime;
        }
    }
}

const updateData = async (courses) =>
{
    const dataset = (await axios.get(`${server}/courses`)).data;

    // Update or create new courses
    for (let [id, data] of Object.entries(dataset))
    {
        if (id in courses)
        {
            if (!courses[id].updateData(data))
            {
                console.info(`Course ${id} is finished.`);
                delete courses[id];
            }
        }
        else
        {
            const newCourse = new Course(data);

            if (!newCourse.updateData(data))
            {
                console.info(`Ignoring course ${id} which is outdated.`);
            }
            else
            {
                console.info(`Course ${id} starting.`);
                courses[id] = newCourse;
            }
        }
    }

    // Remove stale courses
    for (let id of Object.keys(courses))
    {
        if (!(id in dataset))
        {
            delete courses[id];
        }
    }
};

const tick = (courses, time) =>
{
    for (let course of Object.values(courses))
    {
        course.tick(time);
    }
};

const start = () =>
{
    const courses = {};
    let lastFrame = null;
    let lastUpdate = null;

    const update = () =>
    {
        const now = Date.now();

        if (lastUpdate === null || lastUpdate + 5000 <= now)
        {
            lastUpdate = now;
            updateData(courses);
        }

        const time = lastFrame === null ? 0 : now - lastFrame;
        lastFrame = now;
        tick(courses, time);
    };

    return {courses, update};
};

exports.start = start;