function closeMerge(ev: Event, unloading=false): string | void | null {
  if (!mergeWidget) {
    return closeTool(1);
  }
  let savable = getConfigOption('savable');
  for (let md of mergeWidget.model.conflicts) {
    if (md.conflict) {
      if (mergeWidget.model.unsavedChanges && savable) {
        let prompt = 'There are remaining conflicts, and you have unsaved changes. Do you want to close anyway?';
        if (unloading) {
          ev.returnValue = true;
          return prompt;
        }
        alertify.confirm(prompt,
          () => {
            window.onbeforeunload = null!;
            closeTool(1);
          },
          () => {
            ev.preventDefault();
          });
        return null;
      } else {
        let prompt = 'There are remaining conflicts. Do you want to close anyway?';
        if (unloading) {
          ev.returnValue = true;
          return prompt;
        }
        alertify.confirm(prompt,
          () => {
            window.onbeforeunload = null!;
            closeTool(1);
          },
          () => {
            ev.preventDefault();
          });
        return null;
      }
    }
  }
  if (mergeWidget.model.unsavedChanges && savable) {
    let prompt = 'There are unsaved changes. Do you want to close anyway?';
    if (unloading) {
      ev.returnValue = true;
      return prompt;
    }
    alertify.confirm(prompt,
      () => {
        window.onbeforeunload = null!;
        closeTool(0);
      },
      () => {
        ev.preventDefault();
      });
    return null;
  }
  closeTool(0);
  return null;
}

function showError(error: NotifyUserError, url: string, line: number, column: number) {
  let message = error.message.replace('\n', '</br>');
  switch (error.severity) {
  case 'warning':
    alertify.log(message);
    break;
  case 'error':
    alertify.error(message);
    break;
  default:
    alertify.error(message);
  }
}

function extractMergedNotebook(widget: NotebookMergeWidget): nbformat.INotebookContent {
  let nb = widget.model.serialize();
  let validated = widget.validateMerged(nb);
  if (JSON.stringify(nb) !== JSON.stringify(validated)) {
    alertify.error('Value in internal model did not correspond to value from editors. ' +
      'The values in the editors were used, but you should double check the output.');
  }
  return nb;
}

function downloadMerged() {
  if (!mergeWidget) {
    return;
  }
  function download() {
    let filename = getMergeFilename();
    let nb = extractMergedNotebook(mergeWidget!);
    downloadNotebook(nb, filename);
  }
  let conflicted = mergeWidget.model.conflicts.length > 0;
  if (conflicted) {
    alertify.confirm('There are conflicts remaining. ' +
      'Do you still want to download the merge output?', () => {
        download();
      });
  } else {
    download();
  }
}

/**
 * Callback for a failed store of the submitted merged notebook
 */
function onSubmissionFailed(response: string) {
  alertify.error('Was not able to save the notebook! See console and/or server log for details.');
}

/**
 * Callback for a successful store of the submitted merged notebook
 */
function onSubmissionCompleted() {
  alertify.success('Merged notebook saved successfully');
  mergeWidget!.model.unsavedChanges = false;
}

  CELLMERGE_CLASS
} from 'nbdime/lib/merge/widget';


/**
 * DOM class for whether or not to hide unchanged cells
 */
const HIDE_UNCHANGED_CLASS = 'jp-mod-hideUnchanged';

/**
 * Global config data for the Nbdime application.
 */
let configData: any = null;

// Ensure error messages stay open until dismissed.
alertify.delay(0).closeLogOnClick(true);

/**
 *  Make an object fully immutable by freezing each object in it.
 */
function deepFreeze(obj: any): any {

  // Freeze properties before freezing self
  Object.getOwnPropertyNames(obj).forEach(function(name) {
    let prop = obj[name];

    // Freeze prop if it is an object
    if (typeof prop === 'object' && prop !== null && !Object.isFrozen(prop)) {
      deepFreeze(prop);
    }
  });