tracktracker/src/tam/simulation.js

const axios = require("axios");
const turfAlong = require("@turf/along").default;
const turfProjection = require("@turf/projection");
const network = require("./network.json");

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

const findRoute = (from, to) => {
    const queue = [[from, []]];

    while (queue.length) {
        const [head, path] = queue.shift();

        for (const successor of network.stops[head].properties.successors) {
            if (successor === to) {
                return path.concat([head, successor]);
            }

            if (!path.includes(successor)) {
                queue.push([successor, path.concat([head])]);
            }
        }
    }

    return null;
};

class Course {
    constructor(data) {
        this.id = data.id;
        this.prevPassings = [];
        this.nextPassings = [];
        this.state = null;

        // Attributes for the `stopped` state
        this.currentStop = null;
        this.departureTime = 0;

        // 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 null;
        }

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

    updateData(data) {
        this.line = data.line;
        this.finalStop = data.finalStop;
        this.nextPassings = data.nextPassings;

        const now = Date.now();

        if (this.state === null) {
            // Initialize the course on the first available segment
            const index = this.nextPassings.findIndex(
                ([, time]) => time >= now
            );

            if (index === -1) {
                return false;
            }

            if (index === 0) {
                this.arriveToStop(this.nextPassings[index][0]);
            } else {
                this.arriveToStop(this.nextPassings[index - 1][0]);
                this.moveToStop(...this.nextPassings[index]);
            }
        } else if (this.state === "moving") {
            const index = this.nextPassings.findIndex(
                ([stop]) => stop === this.arrivalStop
            );

            if (index === -1 || this.nextPassings[index][1] <= now) {
                // Next stop is not announced or in the past,
                // move towards it as fast as possible
                this.arrivalTime = now;
            } else {
                // On the right track, update the arrival time
                this.arrivalTime = this.nextPassings[index][1];
            }
        } else {
            // (this.state === 'stopped')
            // Try moving to the next stop
            const index = this.nextPassings.findIndex(
                ([stop]) => stop === this.currentStop
            );

            if (index !== -1) {
                if (this.nextPassings[index][1] <= now) {
                    // Current stop is still announced but in the past
                    if (index + 1 < this.nextPassings.length) {
                        // Move to next stop
                        this.moveToStop(...this.nextPassings[index + 1]);
                    } else {
                        // No next stop announced, end of course
                        return false;
                    }
                } else {
                    // Cannot move yet, departure is in the future
                    this.departureTime = this.nextPassings[index][1];
                }
            } else {
                // Current stop is not announced, find the first stop
                // announced in the future to which is connection is
                // possible
                let found = false;

                for (
                    let nextIndex = 0;
                    nextIndex < this.nextPassings.length;
                    ++nextIndex
                ) {
                    const [stop, arrivalTime] = this.nextPassings[nextIndex];

                    if (arrivalTime > now) {
                        const route = findRoute(this.currentStop, stop);

                        if (route !== null) {
                            // Move to the first intermediate stop, guess the
                            // arrival time based on the final arrival time and
                            // the relative distance of the stops
                            const midDistance = network.segments[
                                `${route[0]}-${route[1]}`
                            ].properties.length;

                            let totalDistance = midDistance;

                            for (
                                let midIndex = 1;
                                midIndex + 1 < route.length;
                                ++midIndex
                            ) {
                                totalDistance += network.segments[
                                    `${route[midIndex]}-${route[midIndex + 1]}`
                                ].properties.length;
                            }

                            const midTime = now + (arrivalTime - now) *
                                midDistance / totalDistance;

                            this.moveToStop(route[1], midTime);
                            found = true;
                            break;
                        }
                    }
                }

                if (!found) {
                    // No valid next stop available
                    return false;
                }
            }
        }

        if (this.state === "moving") {
            const segment = this.currentSegment;
            const distance = segment.properties.length - this.traveledDistance;
            const duration = this.arrivalTime - Date.now();

            this.speed = Course.computeSpeed(distance, duration);
        }

        return true;
    }

    tick(time) {
        if (this.state === "moving") {
            // Integrate current speed in travelled distance
            this.traveledDistance += this.speed * time;
            const segment = this.currentSegment;

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

            // Compute updated position and angle based on a small step
            const step = 10; // In meters

            const positions = [
                Math.max(0, this.traveledDistance - step / 2),
                this.traveledDistance,
                this.traveledDistance + step / 2
            ].map(distance => turfProjection.toMercator(turfAlong(
                segment,
                distance / 1000
            )).geometry.coordinates);

            this.angle = Math.atan2(
                positions[0][1] - positions[2][1],
                positions[2][0] - positions[0][0]
            );

            this.position = positions[1];
        }
    }

    /**
     * Transition this course to a state where it has arrived to a stop.
     * @param {string} stop Identifier for the stop to which
     * the course arrives.
     * @returns {undefined}
     */
    arriveToStop(stop) {
        this.state = "stopped";
        this.currentStop = stop;
        this.departureTime = Date.now();
        this.prevPassings.push([stop, Date.now()]);
        this.position = (
            turfProjection.toMercator(network.stops[stop])
                .geometry.coordinates
        );
    }

    /**
     * Transition this course to a state where it is moving to a stop.
     * @param {string} stop Next stop for this course.
     * @param {number} arrivalTime Planned arrival time to that stop.
     * @returns {undefined}
     */
    moveToStop(stop, arrivalTime) {
        const segmentId = `${this.currentStop}-${stop}`;

        if (!(segmentId in network.segments)) {
            console.warn(`Course ${this.id} cannot go from stop
${this.currentStop} to stop ${stop}. Teleporting to ${stop}`);
            this.arriveToStop(stop);
            return;
        }

        const distance = network.segments[segmentId].properties.length;
        const duration = arrivalTime - Date.now();

        if (Course.computeSpeed(distance, duration) === 0) {
            // Speed would be too low, better wait for some time
            return;
        }

        this.state = "moving";
        this.departureStop = this.currentStop;
        this.arrivalStop = stop;
        this.arrivalTime = arrivalTime;
        this.traveledDistance = 0;
        this.speed = 0;
    }

    static computeSpeed(distance, duration) {
        if (duration <= 0) {
            // Late: go to maximum speed
            return 50 / 3600;
        }

        if (distance / duration <= 10 / 3600) {
            // Too slow: pause until speed is sufficient
            return 0;
        }

        return distance / duration;
    }
}

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

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

            if (newCourse.updateData(data)) {
                courses[id] = newCourse;
            }
        }
    }

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

const tick = (courses, time) => {
    for (const 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;