feat(core/EventBus): add createEvent API

Don't expose internal Event representation; instead provide
`EventBus#createEvent(payload)` API to create an internal event, where
needed.

BREAKING CHANGE:

* EventBus.Event constructor got removed. Create event using
`EventBus#createEvent`.

lib/command/CommandStack.js

@@ -1,10 +1,7 @@
 'use strict';
 
 var uniqueBy = require('min-dash').uniqueBy,
-    isArray = require('min-dash').isArray,
-    assign = require('min-dash').assign;
-
-var InternalEvent = require('../core/EventBus').Event;
+    isArray = require('min-dash').isArray;
 
 
 /**
@@ -345,7 +342,7 @@ CommandStack.prototype._fire = function(command, qualifier, event) {
   var names = qualifier ? [ command + '.' + qualifier, qualifier ] : [ command ],
       i, name, result;
 
-  event = assign(new InternalEvent(), event);
+  event = this._eventBus.createEvent(event);
 
   for (i = 0; (name = names[i]); i++) {
     result = this._eventBus.fire('commandStack.' + name, event);

lib/core/EventBus.js

@@ -223,6 +223,22 @@ EventBus.prototype.off = function(event, callback) {
 };
 
 
+/**
+ * Create an EventBus event.
+ *
+ * @param {Object} data
+ *
+ * @return {Object} event, recognized by the eventBus
+ */
+EventBus.prototype.createEvent = function(data) {
+  var event = new InternalEvent();
+
+  event.init(data);
+
+  return event;
+};
+
+
 /**
  * Fires a named event.
  *
@@ -279,12 +295,11 @@ EventBus.prototype.fire = function(type, data) {
 
   // we make sure we fire instances of our home made
   // events here. We wrap them only once, though
-  if (data instanceof Event) {
+  if (data instanceof InternalEvent) {
     // we are fine, we alread have an event
     event = data;
   } else {
-    event = new Event();
-    event.init(data);
+    event = this.createEvent(data);
   }
 
   // ensure we pass the event as the first parameter
@@ -426,19 +441,17 @@ EventBus.prototype._getListeners = function(name) {
 /**
  * A event that is emitted via the event bus.
  */
-function Event() { }
-
-module.exports.Event = Event;
+function InternalEvent() { }
 
-Event.prototype.stopPropagation = function() {
+InternalEvent.prototype.stopPropagation = function() {
   this.cancelBubble = true;
 };
 
-Event.prototype.preventDefault = function() {
+InternalEvent.prototype.preventDefault = function() {
   this.defaultPrevented = true;
 };
 
-Event.prototype.init = function(data) {
+InternalEvent.prototype.init = function(data) {
   assign(this, data || {});
 };
 

lib/features/dragging/Dragging.js

@@ -11,8 +11,6 @@ var domEvent = require('min-dom').event,
     Cursor = require('../../util/Cursor'),
     ClickTrap = require('../../util/ClickTrap');
 
-var EventBusEvent = require('../../core/EventBus').Event;
-
 var DRAG_ACTIVE_CLS = 'djs-drag-active';
 
 
@@ -150,7 +148,14 @@ function Dragging(eventBus, canvas, selection) {
   function fire(type, dragContext) {
     dragContext = dragContext || context;
 
-    var event = assign(new EventBusEvent(), dragContext.payload, dragContext.data, { isTouch: dragContext.isTouch });
+    var event = eventBus.createEvent(
+      assign(
+        {},
+        dragContext.payload,
+        dragContext.data,
+        { isTouch: dragContext.isTouch }
+      )
+    );
 
     // default integration
     if (eventBus.fire('drag.' + type, event) === false) {

test/spec/core/EventBusSpec.js

@@ -2,7 +2,6 @@
 
 var EventBus = require('lib/core/EventBus');
 
-var EventBusEvent = EventBus.Event;
 
 /* global sinon */
 
@@ -83,7 +82,7 @@ describe('core/EventBus', function() {
       it('should be undefined on event if no listeners', function() {
 
         // given
-        var event = new EventBusEvent();
+        var event = eventBus.createEvent();
 
         event.init({ type: 'foo' });
 

test/spec/snapping/SnappingSpec.js

@@ -14,7 +14,7 @@ var canvasEvent = require('../../util/MockEvents').createCanvasEvent;
 
 var SnapContext = require('lib/features/snapping/SnapContext');
 
-var Event = require('lib/core/EventBus').Event;
+var TestHelper = require('test/TestHelper');
 
 
 describe('features/snapping - Snapping', function() {
@@ -98,28 +98,32 @@ describe('features/snapping - Snapping', function() {
 
       var startEvent;
 
-      beforeEach(function() {
-        startEvent = assign(new Event(), {
+      beforeEach(inject(function(eventBus) {
+        startEvent = eventBus.createEvent({
           x: 150,
           y: 150,
           context: {
             shape: shape,
             target: rootElement
           }
         });
-      });
+      }));
 
 
       function moveTo(startEvent, newPosition) {
 
-        return assign(new Event(), startEvent, {
-          x: newPosition.x,
-          y: newPosition.y,
-          dx: newPosition.x - startEvent.x,
-          dy: newPosition.y - startEvent.y
+        return TestHelper.getDiagramJS().invoke(function(eventBus) {
+
+          return eventBus.createEvent(assign(startEvent, {
+            x: newPosition.x,
+            y: newPosition.y,
+            dx: newPosition.x - startEvent.x,
+            dy: newPosition.y - startEvent.y
+          }));
         });
       }
 
+
       it('should init on shape.move.start', inject(function(eventBus) {
 
         // when

test/util/MockEvents.js

@@ -2,8 +2,6 @@
 
 var assign = require('min-dash').assign;
 
-var EventBus = require('../../lib/core/EventBus');
-
 var TestHelper = require('../helper');
 
 
@@ -39,19 +37,17 @@ module.exports.createCanvasEvent = createCanvasEvent;
 
 function createEvent(target, position, data) {
 
-  data = assign({
-    target: target,
-    clientX: position.x,
-    clientY: position.y,
-    offsetX: position.x,
-    offsetY: position.y
-  }, data || {});
-
-  var event = new EventBus.Event();
+  return TestHelper.getDiagramJS().invoke(function(eventBus) {
+    data = assign({
+      target: target,
+      clientX: position.x,
+      clientY: position.y,
+      offsetX: position.x,
+      offsetY: position.y
+    }, data || {});
 
-  event.init(data);
-
-  return event;
+    return eventBus.createEvent(data);
+  });
 }
 
 module.exports.createEvent = createEvent;