/* eslint-env browser */

const subscribtions = {};
const listeners = {};

function subscribe(type) {
  const subscribers = [];
  subscribtions[type] = subscribers;
  const listener = event => {
    for (let i = 0; i < subscribers.length; i++) {
      subscribers[i](event);
    }
  };
  listeners[type] = listener;
  window.addEventListener(type, listener);
}

function addEventListener(type, cb) {
  if (!type || typeof type !== 'string') {
    throw new Error('addEventListener type parameter must be non empty string.');
  }
  if (typeof cb !== 'function') {
    throw new Error('addEventListener listener parameter must be a function.');
  }

  if (!subscribtions.hasOwnProperty(type) || !Array.isArray(subscribtions[type])) {
    subscribe(type);
  }

  subscribtions[type].push(cb);
}

function removeEventListener(type, listener) {
  if (!type || typeof type !== 'string') {
    throw new Error('removeEventListener type parameter must be non empty string.');
  }
  if (typeof cb !== 'function') {
    throw new Error('removeEventListener listener parameter must be a function.');
  }

  if (subscribtions.hasOwnProperty(type)) {
    const subscribers = subscribtions[type];
    const index = subscribers.findIndex(x => x === listener);
    subscribers.splice(index, 1);
    if (subscribers.length === 0) {
      window.removeEventListener(type, listeners[type]);
      delete subscribtions[type];
      delete listeners[type];
    }
  }
}

export default { addEventListener, removeEventListener };