Implement correctly Angular ui-bootstrap date picker

I just integrated the datepicker into a project but it does not work correctly.

HTML

<div class="form-group">
                <label>Date</label>
                <p class="input-group">
        <input type="text" class="form-control" 
         datepicker-popup="mediumDate" 
         is-open="shipment.valuationDatePickerIsOpen" 
        ng-click="shipment.valuationDatePickerOpen()" 
        ng-model="shipment.valuationDate" />
  <span class="input-group-btn">
     <button type="button" class="btn btn-default" 
        ng-click="shipment.valuationDatePickerOpen($event)">
         <i class="fa fa-calendar"></i>
     </button>
</span>
</p>

</div>

Driver

var vm = this;
    // $scope.Eship;

      vm.valuationDate = new Date();
  vm.valuationDatePickerIsOpen = false;
  vm.opens = [];

  $scope.$watch(function () {
       return vm.valuationDatePickerIsOpen;
   },function(value){
      vm.opens.push("valuationDatePickerIsOpen: " + value + " at: " + new Date());
   });

  vm.valuationDatePickerOpen = function ($event) {

      if ($event) {
          $event.preventDefault();
          $event.stopPropagation(); 
      }
      this.valuationDatePickerIsOpen = true;
  };

The current date is displayed as soon as you load the view but nothing happens when you do click in the input or in the button.