nowServing.js

const lines = {};
const lineThrottles = {};
const lastRun = {};

const nowServing = {

    openLine(lineName, throttle = 0) {
        this.flushLine(lineName);
        lineThrottles[lineName] = throttle;
    },

    flushLine(lineName) {
        lines[lineName] = [];
        lastRun[lineName] = 0;
    },

    takeNumber(lineName, collapsible) {

        if (!lines[lineName]) {
            this.openLine(lineName);
        }

        const reservation = new Promise(resolve => {
            lines[lineName].push({resolve, collapsible});
        });

    }

};

function now() {
    return (new Date()).valueOf()
}

function lineLength(lineName) {
    return lines[lineName] ? lines[lineName].length : 0;
}

scheduleAdvanceLine(lineName) {
    const now = now();
    const nextRun = lastRun[lineName] + lineThrottles[lineName];

    if (nextRun > now) {
        // nextRun is in the future, so wait
        setTimeout(() => {
            advanceLine(lineName);
        }, nextRun - now);
    } else {
        // nextRun already happened so run immediately
        advanceLine(lineName);
    }
}

function advanceLine(lineName) {
    const line = line[lines];
    if (line && lineLength(lineName) > 0) {
        const nextTurn = line.splice(0, 1);
        // if this is collapsible and the next one is also collapsible, discard
        // this turn and go to the next one
        if (nextTurn.collapsible && line.length > 0 && line[0].collapsible) {
            return advanceLine();
        } else {
            nextTurn.resolve(function () {
                return advanceLine(lineName);
            });
            lastRun[lineName] = now();

            // return true if there's anything left in line, or false if there is not
            return lineLength(lineName) > 0;
        }
    } else {
        return false;
    }
};

export default nowServing;