//
// const emitter = EventEmitter();
// emitter.on('event', (...args) => console.log(...args));
//

const addHandler = (handlers, handler) => (
  handlers != null
    ? [...handlers, handler]
    : [handler]
);

const call = args => fn => fn(...args);

const callHandlers = (handlers, args) => (
  handlers != null
    ? handlers.forEach(call(args))
    : void 0
);

const on = handlers => (event, handler) => handlers.set(
  event,
  addHandler(
    handlers.get(event), handler
  )
);

const emit = handlers => (event, ...args) => callHandlers(
  handlers.get(event),
  args
);

const EmitterMethods = handlers => ({
  on: on(handlers),
  emit: emit(handlers),
});

export const EventEmitter = () => EmitterMethods(new Map());