[Edit] Add policy for the Edit action

Allow Edit mode only when editable views exist, WTD-1062.

platform/commonUI/browse/bundle.json

@@ -108,7 +108,8 @@
                 "templateUrl": "templates/items/items.html",
                 "uses": [ "composition" ],
                 "gestures": [ "drop" ],
-                "type": "folder"
+                "type": "folder",
+                "editable": false
             }
         ],
         "components": [

platform/commonUI/edit/bundle.json

@@ -68,6 +68,12 @@
                 "depends": [ "$location" ]
             }
         ],
+        "policies": [
+            {
+                "category": "action",
+                "implementation": "policies/EditActionPolicy.js"
+            }
+        ],
         "templates": [
             {
                 "key": "edit-library",

platform/commonUI/edit/src/policies/EditActionPolicy.js

@@ -0,0 +1,61 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * Policy controlling when the `edit` and/or `properties` actions
+         * can appear as applicable actions of the `view-control` category
+         * (shown as buttons in the top-right of browse mode.)
+         * @constructor
+         */
+        function EditActionPolicy() {
+            // Get a count of views which are not flagged as non-editable.
+            function countEditableViews(context) {
+                var domainObject = (context || {}).domainObject,
+                    views = domainObject && domainObject.useCapability('view'),
+                    count = 0;
+
+                // A view is editable unless explicitly flagged as not
+                (views || []).forEach(function (view) {
+                    count += (view.editable !== false) ? 1 : 0;
+                });
+
+                return count;
+            }
+
+            return {
+                /**
+                 * Check whether or not a given action is allowed by this
+                 * policy.
+                 * @param {Action} action the action
+                 * @param context the context
+                 * @returns {boolean} true if not disallowed
+                 */
+                allow: function (action, context) {
+                    var key = action.getMetadata().key,
+                        category = (context || {}).category;
+
+                    // Only worry about actions in the view-control category
+                    if (category === 'view-control') {
+                        // Restrict 'edit' to cases where there are editable
+                        // views (similarly, restrict 'properties' to when
+                        // the converse is true)
+                        if (key === 'edit') {
+                            return countEditableViews(context) > 0;
+                        } else if (key === 'properties') {
+                            return countEditableViews(context) < 1;
+                        }
+                    }
+
+                    // Like all policies, allow by default.
+                    return true;
+                }
+            };
+        }
+
+        return EditActionPolicy;
+    }
+);