- Add code for placing the features information on the frontend

- Add a Features service for examining feature flags on the frontend
- Add a directive (quay-requires) that matches feature flags and, if any one does not match, removes the element from the DOM
- Add a directive (quay-show) that injects the features into the scope so that expressions of the form "Features.BILLING || something" work out of the box to show/hide the element
- Add a directive (quay-classes) that allows for setting of CSS classes on an element based on feature expression(s) such as {"!BILLING": "active"} (e.g. the BILLING flag is set to false, add the class "active".

static/js/app.js

@@ -434,6 +434,37 @@ quayApp = angular.module('quay', ['ngRoute', 'chieffancypants.loadingBar', 'angu
       return metadataService;
     }]);
 
+    $provide.factory('Features', [function() {
+      if (!window.__features) {
+        return {};
+      }
+
+      var features = window.__features;
+      features.getFeature = function(name, opt_defaultValue) {
+        var value = features[name];
+        if (value == null) {
+          return opt_defaultValue;
+        }
+        return value;
+      };
+
+      features.hasFeature = function(name) {
+        return !!features.getFeature(name);
+      };
+      
+      features.matchesFeatures = function(list) {
+        for (var i = 0; i < list.length; ++i) {
+          var value = features.getFeature(list[i]);
+          if (!value) {
+            return false;
+          }
+        }
+        return true;
+      };
+
+      return features;
+    }]);
+
     $provide.factory('ApiService', ['Restangular', function(Restangular) {
       var apiService = {};
 
@@ -1241,6 +1272,117 @@ quayApp = angular.module('quay', ['ngRoute', 'chieffancypants.loadingBar', 'angu
   });
 
 
+function buildConditionalLinker($animate, name, evaluator) {
+  // Based off of a solution found here: http://stackoverflow.com/questions/20325480/angularjs-whats-the-best-practice-to-add-ngif-to-a-directive-programmatically
+  return function ($scope, $element, $attr, ctrl, $transclude) {
+    var block;
+    var childScope;
+    var roles;
+
+    $attr.$observe(name, function (value) {
+      if (evaluator($scope.$eval(value))) {
+        if (!childScope) {
+          childScope = $scope.$new();
+          $transclude(childScope, function (clone) {
+            block = {
+              startNode: clone[0],
+              endNode: clone[clone.length++] = document.createComment(' end ' + name + ': ' + $attr[name] + ' ')
+            };
+            $animate.enter(clone, $element.parent(), $element);
+          });
+        }
+      } else {
+        if (childScope) {
+          childScope.$destroy();
+          childScope = null;
+        }
+
+        if (block) {
+          $animate.leave(getBlockElements(block));
+          block = null;
+        }
+      }
+    });
+  }
+}
+
+quayApp.directive('quayRequire', function ($animate, Features) {
+  return {
+    transclude: 'element',
+    priority: 600,
+    terminal: true,
+    restrict: 'A',
+    link: buildConditionalLinker($animate, 'quayRequire', function(value) {
+      return Features.matchesFeatures(value);
+    })
+  };
+});
+
+
+quayApp.directive('quayShow', function($animate, Features) {
+  return {
+    priority: 590,
+    restrict: 'A',
+    link: function($scope, $element, $attr, ctrl, $transclude) {
+      $scope.Features = Features;
+      $scope.$watch($attr.quayShow, function(result) {
+        $animate[!!result ? 'removeClass' : 'addClass']($element, 'ng-hide');
+      });
+    }
+  };
+});
+
+
+quayApp.directive('quayClasses', function(Features) {
+  return {
+    priority: 580,
+    restrict: 'A',
+    link: function($scope, $element, $attr, ctrl, $transclude) {
+      
+      // Borrowed from ngClass.
+      function flattenClasses(classVal) {
+        if(angular.isArray(classVal)) {
+          return classVal.join(' ');
+        } else if (angular.isObject(classVal)) {
+          var classes = [], i = 0;
+          angular.forEach(classVal, function(v, k) {
+            if (v) {
+              classes.push(k);
+            }
+          });
+          return classes.join(' ');
+        }
+        
+        return classVal;
+      }
+      
+      function removeClass(classVal) {
+        $attr.$removeClass(flattenClasses(classVal));
+      }
+
+
+      function addClass(classVal) {
+        $attr.$addClass(flattenClasses(classVal));
+      }
+
+      $scope.$watch($attr.quayClasses, function(result) {
+        for (var expr in result) {
+          if (!result.hasOwnProperty(expr)) { continue; }
+
+          // Evaluate the expression with the entire features list added.
+          var value = $scope.$eval(expr, Features);
+          if (value) {
+            addClass(result[expr]);
+          } else {
+            removeClass(result[expr]);
+          }
+        }
+      });
+    }
+  };
+});
+
+
 quayApp.directive('entityReference', function () {
   var directiveDefinitionObject = {
     priority: 0,