//     Backbone.js 1.3.3

//     (c) 2010-2016 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://backbonejs.org

import {uniqueId} from "./util/string"
import {once} from "./util/callback"

// Backbone.Events
// ---------------

// A module that can be mixed in to *any object* in order to provide it with
// a custom event channel. You may bind a callback to an event with `on` or
// remove with `off`; `trigger`-ing an event fires all callbacks in
// succession.
//
//     var object = {};
//     extend(object, Backbone.Events);
//     object.on('expand', function(){ alert('expanded'); });
//     object.trigger('expand');
//
export var Events = {};

// Regular expression used to split event strings.
var eventSplitter = /\s+/;

// Iterates over the standard `event, callback` (as well as the fancy multiple
// space-separated events `"change blur", callback` and jQuery-style event
// maps `{event: callback}`).
var eventsApi = function(iteratee, events, name, callback, opts) {
  var i = 0, names;
  if (name && typeof name === 'object') {
    // Handle event maps.
    if (callback !== void 0 && 'context' in opts && opts.context === void 0) opts.context = callback;
    for (names = Object.keys(name); i < names.length ; i++) {
      events = eventsApi(iteratee, events, names[i], name[names[i]], opts);
    }
  } else if (name && eventSplitter.test(name)) {
    // Handle space-separated event names by delegating them individually.
    for (names = name.split(eventSplitter); i < names.length; i++) {
      events = iteratee(events, names[i], callback, opts);
    }
  } else {
    // Finally, standard events.
    events = iteratee(events, name, callback, opts);
  }
  return events;
};

// Bind an event to a `callback` function. Passing `"all"` will bind
// the callback to all events fired.
Events.on = function(name, callback, context) {
  return internalOn(this, name, callback, context);
};

// Guard the `listening` argument from the public API.
var internalOn = function(obj, name, callback, context, listening) {
  obj._events = eventsApi(onApi, obj._events || {}, name, callback, {
    context: context,
    ctx: obj,
    listening: listening
  });

  if (listening) {
    var listeners = obj._listeners || (obj._listeners = {});
    listeners[listening.id] = listening;
  }

  return obj;
};

// Inversion-of-control versions of `on`. Tell *this* object to listen to
// an event in another object... keeping track of what it's listening to
// for easier unbinding later.
Events.listenTo = function(obj, name, callback) {
  if (!obj) return this;
  var id = obj._listenId || (obj._listenId = uniqueId('l'));
  var listeningTo = this._listeningTo || (this._listeningTo = {});
  var listening = listeningTo[id];

  // This object is not listening to any other events on `obj` yet.
  // Setup the necessary references to track the listening callbacks.
  if (!listening) {
    var thisId = this._listenId || (this._listenId = uniqueId('l'));
    listening = listeningTo[id] = {obj: obj, objId: id, id: thisId, listeningTo: listeningTo, count: 0};
  }

  // Bind callbacks on obj, and keep track of them on listening.
  internalOn(obj, name, callback, this, listening);
  return this;
};

// The reducing API that adds a callback to the `events` object.
var onApi = function(events, name, callback, options) {
  if (callback) {
    var handlers = events[name] || (events[name] = []);
    var context = options.context, ctx = options.ctx, listening = options.listening;
    if (listening) listening.count++;

    handlers.push({callback: callback, context: context, ctx: context || ctx, listening: listening});
  }
  return events;
};

// Remove one or many callbacks. If `context` is null, removes all
// callbacks with that function. If `callback` is null, removes all
// callbacks for the event. If `name` is null, removes all bound
// callbacks for all events.
Events.off = function(name, callback, context) {
  if (!this._events) return this;
  this._events = eventsApi(offApi, this._events, name, callback, {
    context: context,
    listeners: this._listeners
  });
  return this;
};

// Tell this object to stop listening to either specific events ... or
// to every object it's currently listening to.
Events.stopListening = function(obj, name, callback) {
  var listeningTo = this._listeningTo;
  if (!listeningTo) return this;

  var ids = obj ? [obj._listenId] : Object.keys(listeningTo);

  for (var i = 0; i < ids.length; i++) {
    var listening = listeningTo[ids[i]];

    // If listening doesn't exist, this object is not currently
    // listening to obj. Break out early.
    if (!listening) break;

    listening.obj.off(name, callback, this);
  }

  return this;
};

// The reducing API that removes a callback from the `events` object.
var offApi = function(events, name, callback, options) {
  if (!events) return;

  var i = 0, listening;
  var context = options.context, listeners = options.listeners;

  // Delete all events listeners and "drop" events.
  if (!name && !callback && !context) {
    var ids = Object.keys(listeners);
    for (; i < ids.length; i++) {
      listening = listeners[ids[i]];
      delete listeners[listening.id];
      delete listening.listeningTo[listening.objId];
    }
    return;
  }

  var names = name ? [name] : Object.keys(events);
  for (; i < names.length; i++) {
    name = names[i];
    var handlers = events[name];

    // Bail out if there are no events stored.
    if (!handlers) break;

    // Replace events if there are any remaining.  Otherwise, clean up.
    var remaining = [];
    for (var j = 0; j < handlers.length; j++) {
      var handler = handlers[j];
      if (
        callback && callback !== handler.callback &&
          callback !== handler.callback._callback ||
            context && context !== handler.context
      ) {
        remaining.push(handler);
      } else {
        listening = handler.listening;
        if (listening && --listening.count === 0) {
          delete listeners[listening.id];
          delete listening.listeningTo[listening.objId];
        }
      }
    }

    // Update tail event if the list has any events.  Otherwise, clean up.
    if (remaining.length) {
      events[name] = remaining;
    } else {
      delete events[name];
    }
  }
  return events;
};

// Bind an event to only be triggered a single time. After the first time
// the callback is invoked, its listener will be removed. If multiple events
// are passed in using the space-separated syntax, the handler will fire
// once for each event, not once for a combination of all events.
Events.once = function(name, callback, context) {
  // Map the event into a `{event: once}` object.
  var events = eventsApi(onceMap, {}, name, callback, this.off.bind(this));
  if (typeof name === 'string' && context == null) callback = void 0;
  return this.on(events, callback, context);
};

// Inversion-of-control versions of `once`.
Events.listenToOnce = function(obj, name, callback) {
  // Map the event into a `{event: once}` object.
  var events = eventsApi(onceMap, {}, name, callback, this.stopListening.bind(this, obj));
  return this.listenTo(obj, events);
};

// Reduces the event callbacks into a map of `{event: onceWrapper}`.
// `offer` unbinds the `onceWrapper` after it has been called.
var onceMap = function(map, name, callback, offer) {
  if (callback) {
    var fn = map[name] = once(function() {
      offer(name, fn);
      callback.apply(this, arguments);
    });
    fn._callback = callback;
  }
  return map;
};

// Trigger one or many events, firing all bound callbacks. Callbacks are
// passed the same arguments as `trigger` is, apart from the event name
// (unless you're listening on `"all"`, which will cause your callback to
// receive the true name of the event as the first argument).
Events.trigger = function(name) {
  if (!this._events) return this;

  var length = Math.max(0, arguments.length - 1);
  var args = Array(length);
  for (var i = 0; i < length; i++) args[i] = arguments[i + 1];

  eventsApi(triggerApi, this._events, name, void 0, args);
  return this;
};

// Handles triggering the appropriate event callbacks.
var triggerApi = function(objEvents, name, callback, args) {
  if (objEvents) {
    var events = objEvents[name];
    var allEvents = objEvents.all;
    if (events && allEvents) allEvents = allEvents.slice();
    if (events) triggerEvents(events, args);
    if (allEvents) triggerEvents(allEvents, [name].concat(args));
  }
  return objEvents;
};

// A difficult-to-believe, but optimized internal dispatch function for
// triggering events. Tries to keep the usual cases speedy (most internal
// Backbone events have 3 arguments).
var triggerEvents = function(events, args) {
  var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
  switch (args.length) {
    case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;
    case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;
    case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;
    case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;
    default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args); return;
  }
};
