blockly/core/keyboard_nav/basic_cursor.js

/**
 * @license
 * Copyright 2019 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @fileoverview The class representing a basic cursor.
 * Used to demo switching between different cursors.
 */
'use strict';

/**
 * The class representing a basic cursor.
 * Used to demo switching between different cursors.
 * @class
 */
goog.module('Blockly.BasicCursor');

const registry = goog.require('Blockly.registry');
const {ASTNode} = goog.require('Blockly.ASTNode');
const {Cursor} = goog.require('Blockly.Cursor');


/**
 * Class for a basic cursor.
 * This will allow the user to get to all nodes in the AST by hitting next or
 * previous.
 * @extends {Cursor}
 * @alias Blockly.BasicCursor
 */
class BasicCursor extends Cursor {
  /**
   * @alias Blockly.BasicCursor
   */
  constructor() {
    super();
  }

  /**
   * Find the next node in the pre order traversal.
   * @return {?ASTNode} The next node, or null if the current node is
   *     not set or there is no next value.
   * @override
   */
  next() {
    const curNode = this.getCurNode();
    if (!curNode) {
      return null;
    }
    const newNode = this.getNextNode_(curNode, this.validNode_);

    if (newNode) {
      this.setCurNode(newNode);
    }
    return newNode;
  }

  /**
   * For a basic cursor we only have the ability to go next and previous, so
   * in will also allow the user to get to the next node in the pre order
   * traversal.
   * @return {?ASTNode} The next node, or null if the current node is
   *     not set or there is no next value.
   * @override
   */
  in() {
    return this.next();
  }

  /**
   * Find the previous node in the pre order traversal.
   * @return {?ASTNode} The previous node, or null if the current node
   *     is not set or there is no previous value.
   * @override
   */
  prev() {
    const curNode = this.getCurNode();
    if (!curNode) {
      return null;
    }
    const newNode = this.getPreviousNode_(curNode, this.validNode_);

    if (newNode) {
      this.setCurNode(newNode);
    }
    return newNode;
  }

  /**
   * For a basic cursor we only have the ability to go next and previous, so
   * out will allow the user to get to the previous node in the pre order
   * traversal.
   * @return {?ASTNode} The previous node, or null if the current node is
   *     not set or there is no previous value.
   * @override
   */
  out() {
    return this.prev();
  }

  /**
   * Uses pre order traversal to navigate the Blockly AST. This will allow
   * a user to easily navigate the entire Blockly AST without having to go in
   * and out levels on the tree.
   * @param {?ASTNode} node The current position in the AST.
   * @param {!function(ASTNode) : boolean} isValid A function true/false
   *     depending on whether the given node should be traversed.
   * @return {?ASTNode} The next node in the traversal.
   * @protected
   */
  getNextNode_(node, isValid) {
    if (!node) {
      return null;
    }
    const newNode = node.in() || node.next();
    if (isValid(newNode)) {
      return newNode;
    } else if (newNode) {
      return this.getNextNode_(newNode, isValid);
    }
    const siblingOrParent = this.findSiblingOrParent_(node.out());
    if (isValid(siblingOrParent)) {
      return siblingOrParent;
    } else if (siblingOrParent) {
      return this.getNextNode_(siblingOrParent, isValid);
    }
    return null;
  }

  /**
   * Reverses the pre order traversal in order to find the previous node. This
   * will allow a user to easily navigate the entire Blockly AST without having
   * to go in and out levels on the tree.
   * @param {?ASTNode} node The current position in the AST.
   * @param {!function(ASTNode) : boolean} isValid A function true/false
   *     depending on whether the given node should be traversed.
   * @return {?ASTNode} The previous node in the traversal or null if no
   *     previous node exists.
   * @protected
   */
  getPreviousNode_(node, isValid) {
    if (!node) {
      return null;
    }
    let newNode = node.prev();

    if (newNode) {
      newNode = this.getRightMostChild_(newNode);
    } else {
      newNode = node.out();
    }
    if (isValid(newNode)) {
      return newNode;
    } else if (newNode) {
      return this.getPreviousNode_(newNode, isValid);
    }
    return null;
  }

  /**
   * Decides what nodes to traverse and which ones to skip. Currently, it
   * skips output, stack and workspace nodes.
   * @param {?ASTNode} node The AST node to check whether it is valid.
   * @return {boolean} True if the node should be visited, false otherwise.
   * @protected
   */
  validNode_(node) {
    let isValid = false;
    const type = node && node.getType();
    if (type === ASTNode.types.OUTPUT || type === ASTNode.types.INPUT ||
        type === ASTNode.types.FIELD || type === ASTNode.types.NEXT ||
        type === ASTNode.types.PREVIOUS || type === ASTNode.types.WORKSPACE) {
      isValid = true;
    }
    return isValid;
  }

  /**
   * From the given node find either the next valid sibling or parent.
   * @param {?ASTNode} node The current position in the AST.
   * @return {?ASTNode} The parent AST node or null if there are no
   *     valid parents.
   * @private
   */
  findSiblingOrParent_(node) {
    if (!node) {
      return null;
    }
    const nextNode = node.next();
    if (nextNode) {
      return nextNode;
    }
    return this.findSiblingOrParent_(node.out());
  }

  /**
   * Get the right most child of a node.
   * @param {?ASTNode} node The node to find the right most child of.
   * @return {?ASTNode} The right most child of the given node, or the node
   *     if no child exists.
   * @private
   */
  getRightMostChild_(node) {
    if (!node.in()) {
      return node;
    }
    let newNode = node.in();
    while (newNode.next()) {
      newNode = newNode.next();
    }
    return this.getRightMostChild_(newNode);
  }
}

/**
 * Name used for registering a basic cursor.
 * @const {string}
 */
BasicCursor.registrationName = 'basicCursor';

registry.register(
    registry.Type.CURSOR, BasicCursor.registrationName, BasicCursor);

exports.BasicCursor = BasicCursor;