// @ts-nocheck
// Trimmed version of "events" library (https://www.npmjs.com/package/events).
// Removed features:
// - Max listener leak warning
// - EventEmitter.prototype.prependListener
// - EventEmitter.prototype.prependOnceListener
// - EventEmitter.prototype.listeners
// - EventEmitter.prototype.rawListeners
// - EventEmitter.prototype.listenerCount
// - EventEmitter.prototype.eventNames
//
// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.

import SplitIO from '../../types/splitio';

var R = typeof Reflect === 'object' ? Reflect : null;
var ReflectApply = R && typeof R.apply === 'function'
  ? R.apply
  : function ReflectApply(target, receiver, args) {
    return Function.prototype.apply.call(target, receiver, args);
  };

export const EventEmitter: { new(): SplitIO.IEventEmitter } = function EventEmitter() {
  EventEmitter.init.call(this);
};

EventEmitter.prototype._events = undefined;
EventEmitter.prototype._eventsCount = 0;

function checkListener(listener) {
  if (typeof listener !== 'function') {
    throw new TypeError('The "listener" argument must be of type Function. Received type ' + typeof listener);
  }
}

EventEmitter.init = function () {

  if (this._events === undefined ||
    this._events === Object.getPrototypeOf(this)._events) {
    this._events = Object.create(null);
    this._eventsCount = 0;
  }
};

EventEmitter.prototype.emit = function emit(type) {
  var args = [];
  for (var i = 1; i < arguments.length; i++) args.push(arguments[i]);
  var doError = (type === 'error');

  var events = this._events;
  if (events !== undefined)
    doError = (doError && events.error === undefined);
  else if (!doError)
    return false;

  // If there is no 'error' event listener then throw.
  if (doError) {
    var er;
    if (args.length > 0)
      er = args[0];
    if (er instanceof Error) {
      // Note: The comments on the `throw` lines are intentional, they show
      // up in Node's output if this results in an unhandled exception.
      throw er; // Unhandled 'error' event
    }
    // At least give some kind of context to the user
    var err = new Error('Unhandled error.' + (er ? ' (' + er.message + ')' : ''));
    err.context = er;
    throw err; // Unhandled 'error' event
  }

  var handler = events[type];

  if (handler === undefined)
    return false;

  if (typeof handler === 'function') {
    ReflectApply(handler, this, args);
  } else {
    var len = handler.length;
    var listeners = arrayClone(handler, len);
    for (let i = 0; i < len; ++i)
      ReflectApply(listeners[i], this, args);
  }

  return true;
};

function _addListener(target, type, listener, prepend) {
  var events;
  var existing;

  checkListener(listener);

  events = target._events;
  if (events === undefined) {
    events = target._events = Object.create(null);
    target._eventsCount = 0;
  } else {
    // To avoid recursion in the case that type === "newListener"! Before
    // adding it to the listeners, first emit "newListener".
    if (events.newListener !== undefined) {
      target.emit('newListener', type,
        listener.listener ? listener.listener : listener);

      // Re-assign `events` because a newListener handler could have caused the
      // this._events to be assigned to a new object
      events = target._events;
    }
    existing = events[type];
  }

  if (existing === undefined) {
    // Optimize the case of one listener. Don't need the extra array object.
    existing = events[type] = listener;
    ++target._eventsCount;
  } else {
    if (typeof existing === 'function') {
      // Adding the second element, need to change to array.
      existing = events[type] =
        prepend ? [listener, existing] : [existing, listener];
      // If we've already got an array, just append.
    } else if (prepend) {
      existing.unshift(listener);
    } else {
      existing.push(listener);
    }
  }

  return target;
}

EventEmitter.prototype.addListener = function addListener(type, listener) {
  return _addListener(this, type, listener, false);
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

function onceWrapper() {
  if (!this.fired) {
    this.target.removeListener(this.type, this.wrapFn);
    this.fired = true;
    if (arguments.length === 0)
      return this.listener.call(this.target);
    return this.listener.apply(this.target, arguments);
  }
}

function _onceWrap(target, type, listener) {
  var state = { fired: false, wrapFn: undefined, target: target, type: type, listener: listener };
  var wrapped = onceWrapper.bind(state);
  wrapped.listener = listener;
  state.wrapFn = wrapped;
  return wrapped;
}

EventEmitter.prototype.once = function once(type, listener) {
  checkListener(listener);
  this.on(type, _onceWrap(this, type, listener));
  return this;
};

// Emits a 'removeListener' event if and only if the listener was removed.
EventEmitter.prototype.removeListener =
  function removeListener(type, listener) {
    var list, events, position, i, originalListener;

    checkListener(listener);

    events = this._events;
    if (events === undefined)
      return this;

    list = events[type];
    if (list === undefined)
      return this;

    if (list === listener || list.listener === listener) {
      if (--this._eventsCount === 0)
        this._events = Object.create(null);
      else {
        delete events[type];
        if (events.removeListener)
          this.emit('removeListener', type, list.listener || listener);
      }
    } else if (typeof list !== 'function') {
      position = -1;

      for (i = list.length - 1; i >= 0; i--) {
        if (list[i] === listener || list[i].listener === listener) {
          originalListener = list[i].listener;
          position = i;
          break;
        }
      }

      if (position < 0)
        return this;

      if (position === 0)
        list.shift();
      else {
        spliceOne(list, position);
      }

      if (list.length === 1)
        events[type] = list[0];

      if (events.removeListener !== undefined)
        this.emit('removeListener', type, originalListener || listener);
    }

    return this;
  };

EventEmitter.prototype.off = EventEmitter.prototype.removeListener;

EventEmitter.prototype.removeAllListeners =
  function removeAllListeners(type) {
    var listeners, events, i;

    events = this._events;
    if (events === undefined)
      return this;

    // not listening for removeListener, no need to emit
    if (events.removeListener === undefined) {
      if (arguments.length === 0) {
        this._events = Object.create(null);
        this._eventsCount = 0;
      } else if (events[type] !== undefined) {
        if (--this._eventsCount === 0)
          this._events = Object.create(null);
        else
          delete events[type];
      }
      return this;
    }

    // emit removeListener for all listeners on all events
    if (arguments.length === 0) {
      var keys = Object.keys(events);
      var key;
      for (i = 0; i < keys.length; ++i) {
        key = keys[i];
        if (key === 'removeListener') continue;
        this.removeAllListeners(key);
      }
      this.removeAllListeners('removeListener');
      this._events = Object.create(null);
      this._eventsCount = 0;
      return this;
    }

    listeners = events[type];

    if (typeof listeners === 'function') {
      this.removeListener(type, listeners);
    } else if (listeners !== undefined) {
      // LIFO order
      for (i = listeners.length - 1; i >= 0; i--) {
        this.removeListener(type, listeners[i]);
      }
    }

    return this;
  };

function arrayClone(arr, n) {
  var copy = new Array(n);
  for (var i = 0; i < n; ++i)
    copy[i] = arr[i];
  return copy;
}

function spliceOne(list, index) {
  for (; index + 1 < list.length; index++)
    list[index] = list[index + 1];
  list.pop();
}