fix(timepicker): move render logic to formatter

- Moves render logic converting model values into date or null object into a formatter, which allows the render function to more correctly render using the viewValue

- remove parentheses as per CR

Relates to #2069

Fixes #3160
Closes #3427

src/timepicker/test/timepicker.spec.js

@@ -101,6 +101,10 @@ describe('timepicker directive', function () {
     expect(getModelState()).toEqual([14, 40]);
   });
 
+  it('should be pristine', function() {
+    expect(element.controller('ngModel').$pristine).toBe(true);
+  });
+
   it('has `selected` current time when model is initially cleared', function() {
     $rootScope.time = null;
     element = $compile('<timepicker ng-model="time"></timepicker>')($rootScope);
@@ -773,6 +777,36 @@ describe('timepicker directive', function () {
     });
   });
 
+  describe('$formatter', function () {
+    var ngModel,
+      date;
+
+    beforeEach(function () {
+      ngModel = element.controller('ngModel');
+      date = new Date('Mon Mar 23 2015 14:40:11 GMT-0700 (PDT)');
+    });
+
+    it('should have one formatter', function () {
+      expect(ngModel.$formatters.length).toBe(1);
+    });
+
+    it('should convert a date to a new reference representing the same date', function () {
+      expect(ngModel.$formatters[0](date)).toEqual(date);
+    });
+
+    it('should convert a valid date string to a date object', function () {
+      expect(ngModel.$formatters[0]('Mon Mar 23 2015 14:40:11 GMT-0700 (PDT)')).toEqual(date);
+    });
+
+    it('should set falsy values as null', function () {
+      expect(ngModel.$formatters[0](undefined)).toBe(null);
+      expect(ngModel.$formatters[0](null)).toBe(null);
+      expect(ngModel.$formatters[0]('')).toBe(null);
+      expect(ngModel.$formatters[0](0)).toBe(null);
+      expect(ngModel.$formatters[0](NaN)).toBe(null);
+    });
+  });
+
   describe('user input validation', function () {
     var changeInputValueTo;
 

src/timepicker/timepicker.js

@@ -19,6 +19,10 @@ angular.module('ui.bootstrap.timepicker', [])
     ngModelCtrl = ngModelCtrl_;
     ngModelCtrl.$render = this.render;
 
+    ngModelCtrl.$formatters.unshift(function (modelValue) {
+      return modelValue ? new Date( modelValue ) : null;
+    });
+
     var hoursInputEl = inputs.eq(0),
         minutesInputEl = inputs.eq(1);
 
@@ -208,7 +212,7 @@ angular.module('ui.bootstrap.timepicker', [])
   };
 
   this.render = function() {
-    var date = ngModelCtrl.$modelValue ? new Date( ngModelCtrl.$modelValue ) : null;
+    var date = ngModelCtrl.$viewValue;
 
     if ( isNaN(date) ) {
       ngModelCtrl.$setValidity('time', false);