const onRunningChanged = (
   sender: Session.IManager,
   models: Session.IModel[]
 ) => {
   editorTracker.forEach(file => {
     const model = find(models, m => file.context.path === m.path);
     if (model) {
       const oldSession = activeSessions[file.id];
       // If there is a matching path, but it is the same
       // session as we previously had, do nothing.
       if (oldSession && oldSession.id === model.id) {
         return;
       }
       // Otherwise, dispose of the old session and reset to
       // a new CompletionConnector.
       if (oldSession) {
         delete activeSessions[file.id];
         oldSession.dispose();
       }
       const session = sessions.connectTo(model);
       activeSessions[file.id] = session;
     } else {
       const session = activeSessions[file.id];
       if (session) {
         session.dispose();
         delete activeSessions[file.id];
       }
     }
   });
 };

 labShell.currentChanged.connect(() => {
   const current = labShell.currentWidget;
   if (current && tracker.has(current)) {
     item.model.editor = (current as IDocumentWidget<
       FileEditor
     >).content.editor;
   }
 });

 /**
  * Update the settings of the current tracker instances.
  */
 function updateTracker(): void {
   tracker.forEach(widget => {
     if (widget.content.editor instanceof CodeMirrorEditor) {
       let cm = widget.content.editor.editor;
       cm.setOption('keyMap', keyMap);
       cm.setOption('theme', theme);
     }
   });
 }

 isActive: () => {
   const current = app.shell.currentWidget;
   return (
     current &&
     (notebookTracker.has(current) ||
       editorTracker.has(current) ||
       consoleTracker.has(current))
   );
 }

 execute: args => {
   keyMap = args['keyMap'] as string || 'default';
   tracker.forEach(widget => {
     if (widget.editor instanceof CodeMirrorEditor) {
       let cm = widget.editor.editor;
       cm.setOption('keyMap', keyMap);
     }
   });
   return saveState();
 },

 /**
  * Toggle editor matching brackets
  */
 function toggleMatchBrackets(): Promise<void> {
   matchBrackets = !matchBrackets;
   tracker.forEach(widget => {
     let editor = widget.editor;
     if (editor instanceof CodeMirrorEditor) {
       let cm = editor.editor;
       cm.setOption('matchBrackets', matchBrackets);
     }
   });
   return saveState();
 }

 /**
  * Update the settings of the current tracker instances.
  */
 function updateTracker(): void {
   tracker.forEach(widget => {
     if (widget.content.editor instanceof CodeMirrorEditor) {
       let cm = widget.content.editor.editor;
       cm.setOption('keyMap', keyMap);
       cm.setOption('theme', theme);
       cm.setOption('scrollPastEnd', scrollPastEnd);
       cm.setOption('styleActiveLine', styleActiveLine);
       cm.setOption('styleSelectedText', styleSelectedText);
       cm.setOption('selectionPointer', selectionPointer);
     }
   });
 }

    app.shell.currentChanged.connect((shell, change) => {
      const { oldValue, newValue } = change;

      // Check if we need to disconnect the console listener
      // or the notebook active cell listener
      if (oldValue && consoleTracker.has(oldValue)) {
        (oldValue as ConsolePanel).console.promptCellCreated.disconnect(
          onPromptCreated
        );
      } else if (oldValue && notebookTracker.has(oldValue)) {
        (oldValue as NotebookPanel).content.activeCellChanged.disconnect(
          onActiveCellChanged
        );
      }

      // Wire up the new editor to the model if it exists
      if (newValue && consoleTracker.has(newValue)) {
        (newValue as ConsolePanel).console.promptCellCreated.connect(
          onPromptCreated
        );
        const prompt = (newValue as ConsolePanel).console.promptCell;
        item.model!.editor = prompt && prompt.editor;
      } else if (newValue && notebookTracker.has(newValue)) {
        (newValue as NotebookPanel).content.activeCellChanged.connect(
          onActiveCellChanged
        );
        const cell = (newValue as NotebookPanel).content.activeCell;
        item.model!.editor = cell && cell.editor;
      } else if (newValue && editorTracker.has(newValue)) {
        item.model!.editor = (newValue as IDocumentWidget<
          FileEditor
        >).content.editor;
      } else {
        item.model!.editor = null;
      }
    });

 isActive: () => {
   return (
     app.shell.currentWidget &&
     editorTracker.has(app.shell.currentWidget)
   );
 }