fix: infinite digest loop with ngRepeat + ImmutableJS (#514)

The addition of `ImmutableJS` caused some issues with Angular's digest
loop. Since `Immutable#toJS()` returns a new object/array every time
(that is, different references), it caused AngularJS to get stuck in an
infinite digest loop when using `ngRepeat` over a function that called
`Immutable#toJS()`.

Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

lib/gui/components/drive-selector/templates/drive-selector-modal.tpl.html

@@ -5,7 +5,7 @@
 
 <div class="component-drive-selector-body modal-body">
   <ul class="list-group">
-    <li class="list-group-item" ng-repeat="drive in modal.drives.getDrives()"
+    <li class="list-group-item" ng-repeat="drive in modal.drives.getDrives() track by drive.device"
       ng-disabled="!modal.state.isDriveValid(drive)"
       ng-click="modal.state.isDriveValid(drive) && modal.state.toggleSetDrive(drive)">
         <div>

lib/gui/models/drives.js

@@ -65,6 +65,28 @@ Drives.service('DrivesModel', function() {
     });
   };
 
+  // This workaround is needed to avoid AngularJS from getting
+  // caught in an infinite digest loop when using `ngRepeat`
+  // over a function that returns a mutable version of an
+  // ImmutableJS object.
+  //
+  // The problem is that everytime you call `myImmutableObject.toJS()`
+  // you will get a new object, whose reference is different from
+  // the one you previously got, even if the data is exactly the same.
+  const memoizeImmutableListReference = function(func) {
+    let previous = [];
+
+    return function() {
+      const list = func.apply(this, arguments);
+
+      if (!_.isEqual(list, previous)) {
+        previous = list;
+      }
+
+      return previous;
+    };
+  };
+
   /**
    * @summary Get detected drives
    * @function
@@ -75,9 +97,9 @@ Drives.service('DrivesModel', function() {
    * @example
    * const drives = DrivesModel.getDrives();
    */
-  this.getDrives = function() {
+  this.getDrives = memoizeImmutableListReference(function() {
     return store.getState().toJS().availableDrives;
-  };
+  });
 
 });