let subscriptions = Object.create(null);

function subscribe(evt, func) {

if(typeof func !== 'function') {

throw "Subscribers must be functions"

}

const oldSubscriptions = subscriptions[evt] || [];

oldSubscriptions.push(func);

subscriptions[evt] = oldSubscriptions;

}

function publish(evt) {

let args = Array.prototype.slice.call(arguments, 1);

const subFunctions = subscriptions[evt] || [];

for(let i = 0; i < subFunctions.length; i++) {

subFunctions[i].apply(null, args)

}

}

function unsubscribe(evt, func) {

const oldSubscriptions = subscriptions[evt] || [];

const newSubscriptions = oldSubscriptions.filter((item) => item !== func);

subscriptions[evt] = newSubscriptions;

}

function cancel(evt) {

delete subscriptions[evt];

}

module.exports = {subscribe, publish, unsubscribe, cancel}