actions.tsx

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.

import { KernelMessage } from '@jupyterlab/services';

import {
  IClientSession,
  Clipboard,
  Dialog,
  showDialog
} from '@jupyterlab/apputils';

import { nbformat } from '@jupyterlab/coreutils';

import {
  ICellModel,
  ICodeCellModel,
  CodeCell,
  Cell,
  MarkdownCell
} from '@jupyterlab/cells';

import { ArrayExt, each, toArray } from '@phosphor/algorithm';

import { JSONObject } from '@phosphor/coreutils';

import { ElementExt } from '@phosphor/domutils';

import { ISignal, Signal } from '@phosphor/signaling';

import * as React from 'react';

import { INotebookModel } from './model';

import { Notebook } from './widget';

// The message to display to the user when prompting to trust the notebook.
const TRUST_MESSAGE = (
  <p>
    A trusted Jupyter notebook may execute hidden malicious code when you open
    it.
    <br />
    Selecting trust will re-render this notebook in a trusted state.
    <br />
    For more information, see the
    <a href="https://jupyter-notebook.readthedocs.io/en/stable/security.html">
      Jupyter security documentation
    </a>
  </p>
);

/**
 * The mimetype used for Jupyter cell data.
 */
const JUPYTER_CELL_MIME = 'application/vnd.jupyter.cells';

/**
 * A collection of actions that run against notebooks.
 *
 * #### Notes
 * All of the actions are a no-op if there is no model on the notebook.
 * The actions set the widget `mode` to `'command'` unless otherwise specified.
 * The actions will preserve the selection on the notebook widget unless
 * otherwise specified.
 */
export class NotebookActions {
  /**
   * A signal that emits whenever a cell is run.
   */
  static get executed(): ISignal<any, { notebook: Notebook; cell: Cell }> {
    return Private.executed;
  }

  /**
   * A private constructor for the `NotebookActions` class.
   *
   * #### Notes
   * This class can never be instantiated. Its static member `executed` will be
   * merged with the `NotebookActions` namespace. The reason it exists as a
   * standalone class is because at run time, the `Private.executed` variable
   * does not yet exist, so it needs to be referenced via a getter.
   */
  private constructor() {}
}

/**
 * A namespace for `NotebookActions` static methods.
 */
export namespace NotebookActions {
  /**
   * Split the active cell into two cells.
   *
   * @param widget - The target notebook widget.
   *
   * #### Notes
   * It will preserve the existing mode.
   * The second cell will be activated.
   * The existing selection will be cleared.
   * The leading whitespace in the second cell will be removed.
   * If there is no content, two empty cells will be created.
   * Both cells will have the same type as the original cell.
   * This action can be undone.
   */
  export function splitCell(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.deselectAll();

    const nbModel = notebook.model;
    const index = notebook.activeCellIndex;
    const child = notebook.widgets[index];
    const editor = child.editor;
    const position = editor.getCursorPosition();
    const offset = editor.getOffsetAt(position);
    const orig = child.model.value.text;

    // Create new models to preserve history.
    const clone0 = Private.cloneCell(nbModel, child.model);
    const clone1 = Private.cloneCell(nbModel, child.model);

    if (clone0.type === 'code') {
      (clone0 as ICodeCellModel).outputs.clear();
    }
    clone0.value.text = orig
      .slice(0, offset)
      .replace(/^\n+/, '')
      .replace(/\n+$/, '');
    clone1.value.text = orig
      .slice(offset)
      .replace(/^\n+/, '')
      .replace(/\n+$/, '');

    // Make the changes while preserving history.
    const cells = nbModel.cells;

    cells.beginCompoundOperation();
    cells.set(index, clone0);
    cells.insert(index + 1, clone1);
    cells.endCompoundOperation();

    notebook.activeCellIndex++;
    Private.handleState(notebook, state);
  }

  /**
   * Merge the selected cells.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget mode will be preserved.
   * If only one cell is selected, the next cell will be selected.
   * If the active cell is a code cell, its outputs will be cleared.
   * This action can be undone.
   * The final cell will have the same type as the active cell.
   * If the active cell is a markdown cell, it will be unrendered.
   */
  export function mergeCells(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const toMerge: string[] = [];
    const toDelete: ICellModel[] = [];
    const model = notebook.model;
    const cells = model.cells;
    const primary = notebook.activeCell;
    const active = notebook.activeCellIndex;

    // Get the cells to merge.
    notebook.widgets.forEach((child, index) => {
      if (notebook.isSelectedOrActive(child)) {
        toMerge.push(child.model.value.text);
        if (index !== active) {
          toDelete.push(child.model);
        }
      }
    });

    // Check for only a single cell selected.
    if (toMerge.length === 1) {
      // Bail if it is the last cell.
      if (active === cells.length - 1) {
        return;
      }

      // Otherwise merge with the next cell.
      const cellModel = cells.get(active + 1);

      toMerge.push(cellModel.value.text);
      toDelete.push(cellModel);
    }

    notebook.deselectAll();

    // Create a new cell for the source to preserve history.
    const newModel = Private.cloneCell(model, primary.model);

    newModel.value.text = toMerge.join('\n\n');
    if (newModel.type === 'code') {
      (newModel as ICodeCellModel).outputs.clear();
    }

    // Make the changes while preserving history.
    cells.beginCompoundOperation();
    cells.set(active, newModel);
    toDelete.forEach(cell => {
      cells.removeValue(cell);
    });
    cells.endCompoundOperation();

    // If the original cell is a markdown cell, make sure
    // the new cell is unrendered.
    if (primary instanceof MarkdownCell) {
      (notebook.activeCell as MarkdownCell).rendered = false;
    }

    Private.handleState(notebook, state);
  }

  /**
   * Delete the selected cells.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The cell after the last selected cell will be activated.
   * It will add a code cell if all cells are deleted.
   * This action can be undone.
   */
  export function deleteCells(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    Private.deleteCells(notebook);
    Private.handleState(notebook, state);
  }

  /**
   * Insert a new code cell above the active cell.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget mode will be preserved.
   * This action can be undone.
   * The existing selection will be cleared.
   * The new cell will the active cell.
   */
  export function insertAbove(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const model = notebook.model;
    const cell = model.contentFactory.createCodeCell({});
    const active = notebook.activeCellIndex;

    model.cells.insert(active, cell);

    // Make the newly inserted cell active.
    notebook.activeCellIndex = active;
    notebook.deselectAll();
    Private.handleState(notebook, state, true);
  }

  /**
   * Insert a new code cell below the active cell.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget mode will be preserved.
   * This action can be undone.
   * The existing selection will be cleared.
   * The new cell will be the active cell.
   */
  export function insertBelow(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const model = notebook.model;
    const cell = model.contentFactory.createCodeCell({});

    model.cells.insert(notebook.activeCellIndex + 1, cell);

    // Make the newly inserted cell active.
    notebook.activeCellIndex++;
    notebook.deselectAll();
    Private.handleState(notebook, state, true);
  }

  /**
   * Move the selected cell(s) down.
   *
   * @param notebook = The target notebook widget.
   */
  export function moveDown(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const cells = notebook.model.cells;
    const widgets = notebook.widgets;

    cells.beginCompoundOperation();
    for (let i = cells.length - 2; i > -1; i--) {
      if (notebook.isSelectedOrActive(widgets[i])) {
        if (!notebook.isSelectedOrActive(widgets[i + 1])) {
          cells.move(i, i + 1);
          if (notebook.activeCellIndex === i) {
            notebook.activeCellIndex++;
          }
          notebook.select(widgets[i + 1]);
          notebook.deselect(widgets[i]);
        }
      }
    }
    cells.endCompoundOperation();
    Private.handleState(notebook, state, true);
  }

  /**
   * Move the selected cell(s) up.
   *
   * @param widget - The target notebook widget.
   */
  export function moveUp(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const cells = notebook.model.cells;
    const widgets = notebook.widgets;

    cells.beginCompoundOperation();
    for (let i = 1; i < cells.length; i++) {
      if (notebook.isSelectedOrActive(widgets[i])) {
        if (!notebook.isSelectedOrActive(widgets[i - 1])) {
          cells.move(i, i - 1);
          if (notebook.activeCellIndex === i) {
            notebook.activeCellIndex--;
          }
          notebook.select(widgets[i - 1]);
          notebook.deselect(widgets[i]);
        }
      }
    }
    cells.endCompoundOperation();
    Private.handleState(notebook, state, true);
  }

  /**
   * Change the selected cell type(s).
   *
   * @param notebook - The target notebook widget.
   *
   * @param value - The target cell type.
   *
   * #### Notes
   * It should preserve the widget mode.
   * This action can be undone.
   * The existing selection will be cleared.
   * Any cells converted to markdown will be unrendered.
   */
  export function changeCellType(
    notebook: Notebook,
    value: nbformat.CellType
  ): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    Private.changeCellType(notebook, value);
    Private.handleState(notebook, state);
  }

  /**
   * Run the selected cell(s).
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * The last selected cell will be activated, but not scrolled into view.
   * The existing selection will be cleared.
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   */
  export function run(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    if (!notebook.model || !notebook.activeCell) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);
    const promise = Private.runSelected(notebook, session);

    Private.handleRunState(notebook, state, false);
    return promise;
  }

  /**
   * Run the selected cell(s) and advance to the next cell.
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * The existing selection will be cleared.
   * The cell after the last selected cell will be activated and scrolled into view.
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   * If the last selected cell is the last cell, a new code cell
   * will be created in `'edit'` mode.  The new cell creation can be undone.
   */
  export function runAndAdvance(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    if (!notebook.model || !notebook.activeCell) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);
    const promise = Private.runSelected(notebook, session);
    const model = notebook.model;

    if (notebook.activeCellIndex === notebook.widgets.length - 1) {
      const cell = model.contentFactory.createCodeCell({});

      model.cells.push(cell);
      notebook.activeCellIndex++;
      notebook.mode = 'edit';
    } else {
      notebook.activeCellIndex++;
    }
    Private.handleRunState(notebook, state, true);
    return promise;
  }

  /**
   * Run the selected cell(s) and insert a new code cell.
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   * The widget mode will be set to `'edit'` after running.
   * The existing selection will be cleared.
   * The cell insert can be undone.
   * The new cell will be scrolled into view.
   */
  export function runAndInsert(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    if (!notebook.model || !notebook.activeCell) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);
    const promise = Private.runSelected(notebook, session);
    const model = notebook.model;
    const cell = model.contentFactory.createCodeCell({});

    model.cells.insert(notebook.activeCellIndex + 1, cell);
    notebook.activeCellIndex++;
    notebook.mode = 'edit';
    Private.handleRunState(notebook, state, true);
    return promise;
  }

  /**
   * Run all of the cells in the notebook.
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * The existing selection will be cleared.
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   * The last cell in the notebook will be activated and scrolled into view.
   */
  export function runAll(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    if (!notebook.model || !notebook.activeCell) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(child => {
      notebook.select(child);
    });

    const promise = Private.runSelected(notebook, session);

    Private.handleRunState(notebook, state, true);
    return promise;
  }

  /**
   * Run all of the cells before the currently active cell (exclusive).
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * The existing selection will be cleared.
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   * The currently active cell will remain selected.
   */
  export function runAllAbove(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    const { activeCell, activeCellIndex, model } = notebook;

    if (!model || !activeCell || activeCellIndex < 1) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);

    notebook.activeCellIndex--;
    notebook.deselectAll();
    for (let i = 0; i < notebook.activeCellIndex; ++i) {
      notebook.select(notebook.widgets[i]);
    }

    const promise = Private.runSelected(notebook, session);

    notebook.activeCellIndex++;
    Private.handleRunState(notebook, state, true);
    return promise;
  }

  /**
   * Run all of the cells after the currently active cell (inclusive).
   *
   * @param notebook - The target notebook widget.
   *
   * @param session - The optional client session object.
   *
   * #### Notes
   * The existing selection will be cleared.
   * An execution error will prevent the remaining code cells from executing.
   * All markdown cells will be rendered.
   * The last cell in the notebook will be activated and scrolled into view.
   */
  export function runAllBelow(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    if (!notebook.model || !notebook.activeCell) {
      return Promise.resolve(false);
    }

    const state = Private.getState(notebook);

    notebook.deselectAll();
    for (let i = notebook.activeCellIndex; i < notebook.widgets.length; ++i) {
      notebook.select(notebook.widgets[i]);
    }

    const promise = Private.runSelected(notebook, session);

    Private.handleRunState(notebook, state, true);
    return promise;
  }

  /**
   * Select the above the active cell.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget mode will be preserved.
   * This is a no-op if the first cell is the active cell.
   * The existing selection will be cleared.
   */
  export function selectAbove(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    if (notebook.activeCellIndex === 0) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.activeCellIndex -= 1;
    notebook.deselectAll();
    Private.handleState(notebook, state, true);
  }

  /**
   * Select the cell below the active cell.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget mode will be preserved.
   * This is a no-op if the last cell is the active cell.
   * The existing selection will be cleared.
   */
  export function selectBelow(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    if (notebook.activeCellIndex === notebook.widgets.length - 1) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.activeCellIndex += 1;
    notebook.deselectAll();
    Private.handleState(notebook, state, true);
  }

  /**
   * Extend the selection to the cell above.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * This is a no-op if the first cell is the active cell.
   * The new cell will be activated.
   */
  export function extendSelectionAbove(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    // Do not wrap around.
    if (notebook.activeCellIndex === 0) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.mode = 'command';
    notebook.extendContiguousSelectionTo(notebook.activeCellIndex - 1);
    Private.handleState(notebook, state, true);
  }

  /**
   * Extend the selection to the cell below.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * This is a no-op if the last cell is the active cell.
   * The new cell will be activated.
   */
  export function extendSelectionBelow(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    // Do not wrap around.
    if (notebook.activeCellIndex === notebook.widgets.length - 1) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.mode = 'command';
    notebook.extendContiguousSelectionTo(notebook.activeCellIndex + 1);
    Private.handleState(notebook, state, true);
  }

  /**
   * Select all of the cells of the notebook.
   *
   * @param notebook - the target notebook widget.
   */
  export function selectAll(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    notebook.widgets.forEach(child => {
      notebook.select(child);
    });
  }

  /**
   * Deselect all of the cells of the notebook.
   *
   * @param notebook - the targe notebook widget.
   */
  export function deselectAll(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }
    notebook.deselectAll();
  }

  /**
   * Copy the selected cell data to a clipboard.
   *
   * @param notebook - The target notebook widget.
   */
  export function copy(notebook: Notebook): void {
    Private.copyOrCut(notebook, false);
  }

  /**
   * Cut the selected cell data to a clipboard.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * This action can be undone.
   * A new code cell is added if all cells are cut.
   */
  export function cut(notebook: Notebook): void {
    Private.copyOrCut(notebook, true);
  }

  /**
   * Paste cells from the application clipboard.
   *
   * @param notebook - The target notebook widget.
   *
   * @param mode - the mode of the paste operation: 'below' pastes cells
   *   below the active cell, 'above' pastes cells above the active cell,
   *   and 'replace' removes the currently selected cells and pastes cells
   *   in their place.
   *
   * #### Notes
   * The last pasted cell becomes the active cell.
   * This is a no-op if there is no cell data on the clipboard.
   * This action can be undone.
   */
  export function paste(
    notebook: Notebook,
    mode: 'below' | 'above' | 'replace' = 'below'
  ): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const clipboard = Clipboard.getInstance();

    if (!clipboard.hasData(JUPYTER_CELL_MIME)) {
      return;
    }

    const state = Private.getState(notebook);
    const values = clipboard.getData(JUPYTER_CELL_MIME) as nbformat.IBaseCell[];
    const model = notebook.model;

    notebook.mode = 'command';

    const newCells = values.map(cell => {
      switch (cell.cell_type) {
        case 'code':
          return model.contentFactory.createCodeCell({ cell });
        case 'markdown':
          return model.contentFactory.createMarkdownCell({ cell });
        default:
          return model.contentFactory.createRawCell({ cell });
      }
    });

    const cells = notebook.model.cells;
    let index: number;

    cells.beginCompoundOperation();

    // Set the starting index of the paste operation depending upon the mode.
    switch (mode) {
      case 'below':
        index = notebook.activeCellIndex;
        break;
      case 'above':
        index = notebook.activeCellIndex - 1;
        break;
      case 'replace':
        // Find the cells to delete.
        const toDelete: number[] = [];

        notebook.widgets.forEach((child, index) => {
          const deletable = child.model.metadata.get('deletable') !== false;

          if (notebook.isSelectedOrActive(child) && deletable) {
            toDelete.push(index);
          }
        });

        // If cells are not deletable, we may not have anything to delete.
        if (toDelete.length > 0) {
          // Delete the cells as one undo event.
          toDelete.reverse().forEach(i => {
            cells.remove(i);
          });
        }
        index = toDelete[0];
        break;
      default:
        break;
    }

    newCells.forEach(cell => {
      cells.insert(++index, cell);
    });
    cells.endCompoundOperation();

    notebook.activeCellIndex += newCells.length;
    notebook.deselectAll();
    Private.handleState(notebook, state);
  }

  /**
   * Undo a cell action.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * This is a no-op if if there are no cell actions to undo.
   */
  export function undo(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.mode = 'command';
    notebook.model.cells.undo();
    notebook.deselectAll();
    Private.handleState(notebook, state);
  }

  /**
   * Redo a cell action.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * This is a no-op if there are no cell actions to redo.
   */
  export function redo(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.mode = 'command';
    notebook.model.cells.redo();
    notebook.deselectAll();
    Private.handleState(notebook, state);
  }

  /**
   * Toggle the line number of all cells.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The original state is based on the state of the active cell.
   * The `mode` of the widget will be preserved.
   */
  export function toggleAllLineNumbers(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const config = notebook.editorConfig;
    const lineNumbers = !(
      config.code.lineNumbers &&
      config.markdown.lineNumbers &&
      config.raw.lineNumbers
    );
    const newConfig = {
      code: { ...config.code, lineNumbers },
      markdown: { ...config.markdown, lineNumbers },
      raw: { ...config.raw, lineNumbers }
    };

    notebook.editorConfig = newConfig;
    Private.handleState(notebook, state);
  }

  /**
   * Toggle whether to record cell timing execution.
   *
   * @param notebook - The target notebook widget.
   */
  export function toggleRecordTiming(notebook: Notebook): void {
    if (!notebook.model) {
      return;
    }
    const currentValue = notebook.model.metadata.get('record_timing') || false;
    notebook.model.metadata.set('record_timing', !currentValue);
  }

  /**
   * Clear the code outputs of the selected cells.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget `mode` will be preserved.
   */
  export function clearOutputs(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    each(notebook.model.cells, (cell: ICodeCellModel, index) => {
      const child = notebook.widgets[index];

      if (notebook.isSelectedOrActive(child) && cell.type === 'code') {
        cell.outputs.clear();
        (child as CodeCell).outputHidden = false;
        cell.executionCount = null;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Clear all the code outputs on the widget.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The widget `mode` will be preserved.
   */
  export function clearAllOutputs(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    each(notebook.model.cells, (cell: ICodeCellModel, index) => {
      const child = notebook.widgets[index];

      if (cell.type === 'code') {
        cell.outputs.clear();
        cell.executionCount = null;
        (child as CodeCell).outputHidden = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Hide the code on selected code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function hideCode(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        cell.inputHidden = true;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Show the code on selected code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function showCode(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        cell.inputHidden = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Hide the code on all code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function hideAllCode(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (cell.model.type === 'code') {
        cell.inputHidden = true;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Show the code on all code cells.
   *
   * @param widget - The target notebook widget.
   */
  export function showAllCode(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (cell.model.type === 'code') {
        cell.inputHidden = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Hide the output on selected code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function hideOutput(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        (cell as CodeCell).outputHidden = true;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Show the output on selected code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function showOutput(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        (cell as CodeCell).outputHidden = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Hide the output on all code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function hideAllOutputs(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (cell.model.type === 'code') {
        (cell as CodeCell).outputHidden = true;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Show the output on all code cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function showAllOutputs(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (cell.model.type === 'code') {
        (cell as CodeCell).outputHidden = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Enable output scrolling for all selected cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function enableOutputScrolling(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        (cell as CodeCell).outputsScrolled = true;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Disable output scrolling for all selected cells.
   *
   * @param notebook - The target notebook widget.
   */
  export function disableOutputScrolling(notebook: Notebook): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      if (notebook.isSelectedOrActive(cell) && cell.model.type === 'code') {
        (cell as CodeCell).outputsScrolled = false;
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Persists the collapsed state of all code cell outputs to the model.
   *
   * @param notebook - The target notebook widget.
   */
  export function persistViewState(notebook: Notebook): void {
    if (!notebook.model) {
      return;
    }

    const state = Private.getState(notebook);

    notebook.widgets.forEach(cell => {
      const { model, inputHidden } = cell;
      const metadata = model.metadata;
      const jupyter = (metadata.get('jupyter') as any) || {};

      if (inputHidden) {
        jupyter.source_hidden = true;
      } else {
        delete jupyter.source_hidden;
      }

      if (cell.model.type === 'code') {
        const { outputHidden, outputsScrolled } = cell as CodeCell;

        // set both metadata keys
        // https://github.com/jupyterlab/jupyterlab/pull/3981#issuecomment-391139167
        if (outputHidden) {
          model.metadata.set('collapsed', true);
          jupyter.outputs_hidden = true;
        } else {
          model.metadata.delete('collapsed');
          delete jupyter.outputs_hidden;
        }

        if (outputsScrolled) {
          model.metadata.set('scrolled', true);
        } else {
          model.metadata.delete('scrolled');
        }
      }

      if (Object.keys(jupyter).length === 0) {
        metadata.delete('jupyter');
      } else {
        metadata.set('jupyter', jupyter);
      }
    });
    Private.handleState(notebook, state);
  }

  /**
   * Set the markdown header level.
   *
   * @param notebook - The target notebook widget.
   *
   * @param level - The header level.
   *
   * #### Notes
   * All selected cells will be switched to markdown.
   * The level will be clamped between 1 and 6.
   * If there is an existing header, it will be replaced.
   * There will always be one blank space after the header.
   * The cells will be unrendered.
   */
  export function setMarkdownHeader(notebook: Notebook, level: number) {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = Private.getState(notebook);
    const cells = notebook.model.cells;

    level = Math.min(Math.max(level, 1), 6);
    notebook.widgets.forEach((child, index) => {
      if (notebook.isSelectedOrActive(child)) {
        Private.setMarkdownHeader(cells.get(index), level);
      }
    });
    Private.changeCellType(notebook, 'markdown');
    Private.handleState(notebook, state);
  }

  /**
   * Trust the notebook after prompting the user.
   *
   * @param notebook - The target notebook widget.
   *
   * @returns a promise that resolves when the transaction is finished.
   *
   * #### Notes
   * No dialog will be presented if the notebook is already trusted.
   */
  export function trust(notebook: Notebook): Promise<void> {
    if (!notebook.model) {
      return Promise.resolve();
    }
    // Do nothing if already trusted.

    const cells = toArray(notebook.model.cells);
    const trusted = cells.every(cell => cell.trusted);

    if (trusted) {
      return showDialog({
        body: 'Notebook is already trusted',
        buttons: [Dialog.okButton()]
      }).then(() => undefined);
    }

    return showDialog({
      body: TRUST_MESSAGE,
      title: 'Trust this notebook?',
      buttons: [Dialog.cancelButton(), Dialog.warnButton()]
    }).then(result => {
      if (result.button.accept) {
        cells.forEach(cell => {
          cell.trusted = true;
        });
      }
    });
  }
}

/**
 * A namespace for private data.
 */
namespace Private {
  /**
   * A signal that emits whenever a cell is run.
   */
  export const executed = new Signal<any, { notebook: Notebook; cell: Cell }>(
    {}
  );

  /**
   * The interface for a widget state.
   */
  export interface IState {
    /**
     * Whether the widget had focus.
     */
    wasFocused: boolean;

    /**
     * The active cell before the action.
     */
    activeCell: Cell;
  }

  /**
   * Get the state of a widget before running an action.
   */
  export function getState(notebook: Notebook): IState {
    return {
      wasFocused: notebook.node.contains(document.activeElement),
      activeCell: notebook.activeCell
    };
  }

  /**
   * Handle the state of a widget after running an action.
   */
  export function handleState(
    notebook: Notebook,
    state: IState,
    scrollIfNeeded = false
  ): void {
    const { activeCell, node } = notebook;

    if (state.wasFocused || notebook.mode === 'edit') {
      notebook.activate();
    }

    if (scrollIfNeeded) {
      ElementExt.scrollIntoViewIfNeeded(node, activeCell.node);
    }
  }

  /**
   * Handle the state of a widget after running a run action.
   */
  export function handleRunState(
    notebook: Notebook,
    state: IState,
    scroll = false
  ): void {
    if (state.wasFocused || notebook.mode === 'edit') {
      notebook.activate();
    }
    if (scroll) {
      // Scroll to the top of the previous active cell output.
      const rect = state.activeCell.inputArea.node.getBoundingClientRect();

      notebook.scrollToPosition(rect.bottom, 45);
    }
  }

  /**
   * Clone a cell model.
   */
  export function cloneCell(
    model: INotebookModel,
    cell: ICellModel
  ): ICellModel {
    switch (cell.type) {
      case 'code':
        // TODO why isn't modeldb or id passed here?
        return model.contentFactory.createCodeCell({ cell: cell.toJSON() });
      case 'markdown':
        // TODO why isn't modeldb or id passed here?
        return model.contentFactory.createMarkdownCell({ cell: cell.toJSON() });
      default:
        // TODO why isn't modeldb or id passed here?
        return model.contentFactory.createRawCell({ cell: cell.toJSON() });
    }
  }

  /**
   * Run the selected cells.
   */
  export function runSelected(
    notebook: Notebook,
    session?: IClientSession
  ): Promise<boolean> {
    notebook.mode = 'command';

    let lastIndex = notebook.activeCellIndex;
    const selected = notebook.widgets.filter((child, index) => {
      const active = notebook.isSelectedOrActive(child);

      if (active) {
        lastIndex = index;
      }

      return active;
    });

    notebook.activeCellIndex = lastIndex;
    notebook.deselectAll();

    return Promise.all(selected.map(child => runCell(notebook, child, session)))
      .then(results => {
        if (notebook.isDisposed) {
          return false;
        }

        // Post an update request.
        notebook.update();

        return results.every(result => result);
      })
      .catch(reason => {
        if (reason.message === 'KernelReplyNotOK') {
          selected.map((cell: CodeCell) => {
            // Remove '*' prompt from cells that didn't execute
            if (cell.model.executionCount == null) {
              cell.setPrompt('');
            }
          });
        } else {
          throw reason;
        }

        notebook.update();

        return false;
      });
  }

  /**
   * Run a cell.
   */
  function runCell(
    notebook: Notebook,
    cell: Cell,
    session?: IClientSession
  ): Promise<boolean> {
    switch (cell.model.type) {
      case 'markdown':
        (cell as MarkdownCell).rendered = true;
        cell.inputHidden = false;
        executed.emit({ notebook, cell });
        break;
      case 'code':
        if (session) {
          return CodeCell.execute(cell as CodeCell, session, {
            deletedCells: notebook.model.deletedCells,
            recordTiming: notebook.model.metadata.get('record_timing') || false
          })
            .then(reply => {
              notebook.model.deletedCells.splice(
                0,
                notebook.model.deletedCells.length
              );
              if (cell.isDisposed) {
                return false;
              }

              if (!reply) {
                return true;
              }

              if (reply.content.status === 'ok') {
                const content = reply.content as KernelMessage.IExecuteOkReply;

                if (content.payload && content.payload.length) {
                  handlePayload(content, notebook, cell);
                }

                return true;
              } else {
                throw new Error('KernelReplyNotOK');
              }
            })
            .catch(reason => {
              if (reason.message !== 'Canceled') {
                throw reason;
              }

              return false;
            })
            .then(ran => {
              if (ran) {
                executed.emit({ notebook, cell });
              }

              return ran;
            });
        }
        (cell.model as ICodeCellModel).executionCount = null;
        break;
      default:
        break;
    }

    return Promise.resolve(true);
  }

  /**
   * Handle payloads from an execute reply.
   *
   * #### Notes
   * Payloads are deprecated and there are no official interfaces for them in
   * the kernel type definitions.
   * See [Payloads (DEPRECATED)](https://jupyter-client.readthedocs.io/en/latest/messaging.html#payloads-deprecated).
   */
  function handlePayload(
    content: KernelMessage.IExecuteOkReply,
    notebook: Notebook,
    cell: Cell
  ) {
    const setNextInput = content.payload.filter(i => {
      return (i as any).source === 'set_next_input';
    })[0];

    if (!setNextInput) {
      return;
    }

    const text = (setNextInput as any).text;
    const replace = (setNextInput as any).replace;

    if (replace) {
      cell.model.value.text = text;
      return;
    }

    // Create a new code cell and add as the next cell.
    const newCell = notebook.model.contentFactory.createCodeCell({});
    const cells = notebook.model.cells;
    const index = ArrayExt.firstIndexOf(toArray(cells), cell.model);

    newCell.value.text = text;
    if (index === -1) {
      cells.push(newCell);
    } else {
      cells.insert(index + 1, newCell);
    }
  }

  /**
   * Copy or cut the selected cell data to the application clipboard.
   *
   * @param notebook - The target notebook widget.
   *
   * @param cut - Whether to copy or cut.
   */
  export function copyOrCut(notebook: Notebook, cut: boolean): void {
    if (!notebook.model || !notebook.activeCell) {
      return;
    }

    const state = getState(notebook);
    const clipboard = Clipboard.getInstance();

    notebook.mode = 'command';
    clipboard.clear();

    let data = notebook.widgets
      .filter(cell => notebook.isSelectedOrActive(cell))
      .map(cell => cell.model.toJSON())
      .map(cellJSON => {
        if ((cellJSON.metadata as JSONObject).deletable !== undefined) {
          delete (cellJSON.metadata as JSONObject).deletable;
        }
        return cellJSON;
      });

    clipboard.setData(JUPYTER_CELL_MIME, data);
    if (cut) {
      deleteCells(notebook);
    } else {
      notebook.deselectAll();
    }
    handleState(notebook, state);
  }

  /**
   * Change the selected cell type(s).
   *
   * @param notebook - The target notebook widget.
   *
   * @param value - The target cell type.
   *
   * #### Notes
   * It should preserve the widget mode.
   * This action can be undone.
   * The existing selection will be cleared.
   * Any cells converted to markdown will be unrendered.
   */
  export function changeCellType(
    notebook: Notebook,
    value: nbformat.CellType
  ): void {
    const model = notebook.model;
    const cells = model.cells;

    cells.beginCompoundOperation();
    notebook.widgets.forEach((child, index) => {
      if (!notebook.isSelectedOrActive(child)) {
        return;
      }
      if (child.model.type !== value) {
        const cell = child.model.toJSON();
        let newCell: ICellModel;

        switch (value) {
          case 'code':
            newCell = model.contentFactory.createCodeCell({ cell });
            break;
          case 'markdown':
            newCell = model.contentFactory.createMarkdownCell({ cell });
            if (child.model.type === 'code') {
              newCell.trusted = false;
            }
            break;
          default:
            newCell = model.contentFactory.createRawCell({ cell });
            if (child.model.type === 'code') {
              newCell.trusted = false;
            }
        }
        cells.set(index, newCell);
      }
      if (value === 'markdown') {
        // Fetch the new widget and unrender it.
        child = notebook.widgets[index];
        (child as MarkdownCell).rendered = false;
      }
    });
    cells.endCompoundOperation();
    notebook.deselectAll();
  }

  /**
   * Delete the selected cells.
   *
   * @param notebook - The target notebook widget.
   *
   * #### Notes
   * The cell after the last selected cell will be activated.
   * If the last cell is deleted, then the previous one will be activated.
   * It will add a code cell if all cells are deleted.
   * This action can be undone.
   */
  export function deleteCells(notebook: Notebook): void {
    const model = notebook.model;
    const cells = model.cells;
    const toDelete: number[] = [];

    notebook.mode = 'command';

    // Find the cells to delete.
    notebook.widgets.forEach((child, index) => {
      const deletable = child.model.metadata.get('deletable') !== false;

      if (notebook.isSelectedOrActive(child) && deletable) {
        toDelete.push(index);
        notebook.model.deletedCells.push(child.model.id);
      }
    });

    // If cells are not deletable, we may not have anything to delete.
    if (toDelete.length > 0) {
      // Delete the cells as one undo event.
      cells.beginCompoundOperation();
      // Delete cells in reverse order to maintain the correct indices.
      toDelete.reverse().forEach(index => {
        cells.remove(index);
      });
      // Add a new cell if the notebook is empty. This is done
      // within the compound operation to make the deletion of
      // a notebook's last cell undoable.
      if (!cells.length) {
        cells.push(model.contentFactory.createCodeCell({}));
      }
      cells.endCompoundOperation();

      // Select the *first* interior cell not deleted or the cell
      // *after* the last selected cell.
      // Note: The activeCellIndex is clamped to the available cells,
      // so if the last cell is deleted the previous cell will be activated.
      // The *first* index is the index of the last cell in the initial
      // toDelete list due to the `reverse` operation above.
      notebook.activeCellIndex = toDelete[0] - toDelete.length + 1;
    }

    // Deselect any remaining, undeletable cells. Do this even if we don't
    // delete anything so that users are aware *something* happened.
    notebook.deselectAll();
  }

  /**
   * Set the markdown header level of a cell.
   */
  export function setMarkdownHeader(cell: ICellModel, level: number) {
    // Remove existing header or leading white space.
    let source = cell.value.text;
    const regex = /^(#+\s*)|^(\s*)/;
    const newHeader = Array(level + 1).join('#') + ' ';
    const matches = regex.exec(source);

    if (matches) {
      source = source.slice(matches[0].length);
    }
    cell.value.text = newHeader + source;
  }
}