Scheduler

scheduler.js

let events = [];
let timeout = null;
let interval = 100;

const getScheduled = () => {
    let now = Date.now();

    return events.filter(event => {
        return (event.lastInvoked + event.interval) < now;
    });
};

const start = () => {
    if (timeout) {
        stop();
    }

    timeout = setTimeout(scheduler, interval);
};

const stop = () => {
    timeout = clearTimeout(timeout);
};

const add = (interval, repeat, callback) => {
    let lastInvoked = Date.now();
    let id = Math.random().toString(36).substring(2, 10);
    let event = { id, interval, repeat, callback, lastInvoked };

    events.push(event);

    // Start the scheduler if not aleady started.
    if (!timeout && events.length > 0) {
        start();
    }

    return event;
};

const remove = event => {
    let index = events.findIndex(e => e.id === event.id);

    if (index !== -1) {
        events.splice(index, 1);

        if (timeout && events.length === 0) {
            stop();
        }
    }
};

const scheduler = () => {
    let scheduled = getScheduled();
    
    scheduled.forEach(event => {
        event.callback();
        event.lastInvoked = Date.now();
        
        if (!event.repeat) {
            remove(event);
        }
    });

    if (timeout) {
        start();
    }
};

module.exports = {
    add,
    remove
};