blockly/core/utils/dom.ts

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

/**
 * Utility methods for DOM manipulation.
 * These methods are not specific to Blockly, and could be factored out into
 * a JavaScript framework such as Closure.
 *
 * @namespace Blockly.utils.dom
 */
import * as goog from '../../closure/goog/goog.js';
goog.declareModuleId('Blockly.utils.dom');

import type {Svg} from './svg.js';


/**
 * Required name space for SVG elements.
 *
 * @alias Blockly.utils.dom.SVG_NS
 */
export const SVG_NS = 'http://www.w3.org/2000/svg';

/**
 * Required name space for HTML elements.
 *
 * @alias Blockly.utils.dom.HTML_NS
 */
export const HTML_NS = 'http://www.w3.org/1999/xhtml';

/**
 * Required name space for XLINK elements.
 *
 * @alias Blockly.utils.dom.XLINK_NS
 */
export const XLINK_NS = 'http://www.w3.org/1999/xlink';

/**
 * Node type constants.
 * https://developer.mozilla.org/en-US/docs/Web/API/Node/nodeType
 *
 * @alias Blockly.utils.dom.NodeType
 */
export enum NodeType {
  ELEMENT_NODE = 1,
  TEXT_NODE = 3,
  COMMENT_NODE = 8,
  DOCUMENT_POSITION_CONTAINED_BY = 16
}

/** Temporary cache of text widths. */
let cacheWidths: {[key: string]: number}|null = null;

/** Number of current references to cache. */
let cacheReference = 0;

/** A HTML canvas context used for computing text width. */
let canvasContext: CanvasRenderingContext2D|null = null;

/**
 * Helper method for creating SVG elements.
 *
 * @param name Element's tag name.
 * @param attrs Dictionary of attribute names and values.
 * @param opt_parent Optional parent on which to append the element.
 * @returns if name is a string or a more specific type if it a member of Svg.
 * @alias Blockly.utils.dom.createSvgElement
 */
export function createSvgElement<T extends SVGElement>(
    name: string|Svg<T>, attrs: {[key: string]: string|number},
    opt_parent?: Element|null): T {
  const e = document.createElementNS(SVG_NS, String(name)) as T;
  for (const key in attrs) {
    e.setAttribute(key, `${attrs[key]}`);
  }
  if (opt_parent) {
    opt_parent.appendChild(e);
  }
  return e;
}

/**
 * Add a CSS class to a element.
 *
 * @param element DOM element to add class to.
 * @param className Name of class to add.
 * @returns True if class was added, false if already present.
 * @alias Blockly.utils.dom.addClass
 */
export function addClass(element: Element, className: string): boolean {
  if (element.classList.contains(className)) {
    return false;
  }
  element.classList.add(className);
  return true;
}

/**
 * Removes multiple calsses from an element.
 *
 * @param element DOM element to remove classes from.
 * @param classNames A string of one or multiple class names for an element.
 * @alias Blockly.utils.dom.removeClasses
 */
export function removeClasses(element: Element, classNames: string) {
  const classList = classNames.split(' ');
  for (let i = 0; i < classList.length; i++) {
    element.classList.remove(classList[i]);
  }
}

/**
 * Remove a CSS class from a element.
 *
 * @param element DOM element to remove class from.
 * @param className Name of class to remove.
 * @returns True if class was removed, false if never present.
 * @alias Blockly.utils.dom.removeClass
 */
export function removeClass(element: Element, className: string): boolean {
  if (!element.classList.contains(className)) {
    return false;
  }
  element.classList.remove(className);
  return true;
}

/**
 * Checks if an element has the specified CSS class.
 *
 * @param element DOM element to check.
 * @param className Name of class to check.
 * @returns True if class exists, false otherwise.
 * @alias Blockly.utils.dom.hasClass
 */
export function hasClass(element: Element, className: string): boolean {
  return element.classList.contains(className);
}

/**
 * Removes a node from its parent. No-op if not attached to a parent.
 *
 * @param node The node to remove.
 * @returns The node removed if removed; else, null.
 * @alias Blockly.utils.dom.removeNode
 */
// Copied from Closure goog.dom.removeNode
export function removeNode(node: Node|null): Node|null {
  return node && node.parentNode ? node.parentNode.removeChild(node) : null;
}

/**
 * Insert a node after a reference node.
 * Contrast with node.insertBefore function.
 *
 * @param newNode New element to insert.
 * @param refNode Existing element to precede new node.
 * @alias Blockly.utils.dom.insertAfter
 */
export function insertAfter(newNode: Element, refNode: Element) {
  const siblingNode = refNode.nextSibling;
  const parentNode = refNode.parentNode;
  if (!parentNode) {
    throw Error('Reference node has no parent.');
  }
  if (siblingNode) {
    parentNode.insertBefore(newNode, siblingNode);
  } else {
    parentNode.appendChild(newNode);
  }
}

/**
 * Whether a node contains another node.
 *
 * @param parent The node that should contain the other node.
 * @param descendant The node to test presence of.
 * @returns Whether the parent node contains the descendant node.
 * @alias Blockly.utils.dom.containsNode
 */
export function containsNode(parent: Node, descendant: Node): boolean {
  return !!(
      parent.compareDocumentPosition(descendant) &
      NodeType.DOCUMENT_POSITION_CONTAINED_BY);
}

/**
 * Sets the CSS transform property on an element. This function sets the
 * non-vendor-prefixed and vendor-prefixed versions for backwards compatibility
 * with older browsers. See https://caniuse.com/#feat=transforms2d
 *
 * @param element Element to which the CSS transform will be applied.
 * @param transform The value of the CSS `transform` property.
 * @alias Blockly.utils.dom.setCssTransform
 */
export function setCssTransform(
    element: HTMLElement|SVGElement, transform: string) {
  element.style['transform'] = transform;
  element.style['-webkit-transform' as any] = transform;
}

/**
 * Start caching text widths. Every call to this function MUST also call
 * stopTextWidthCache. Caches must not survive between execution threads.
 *
 * @alias Blockly.utils.dom.startTextWidthCache
 */
export function startTextWidthCache() {
  cacheReference++;
  if (!cacheWidths) {
    cacheWidths = Object.create(null);
  }
}

/**
 * Stop caching field widths. Unless caching was already on when the
 * corresponding call to startTextWidthCache was made.
 *
 * @alias Blockly.utils.dom.stopTextWidthCache
 */
export function stopTextWidthCache() {
  cacheReference--;
  if (!cacheReference) {
    cacheWidths = null;
  }
}

/**
 * Gets the width of a text element, caching it in the process.
 *
 * @param textElement An SVG 'text' element.
 * @returns Width of element.
 * @alias Blockly.utils.dom.getTextWidth
 */
export function getTextWidth(textElement: SVGTextElement): number {
  const key = textElement.textContent + '\n' + textElement.className.baseVal;
  let width;
  // Return the cached width if it exists.
  if (cacheWidths) {
    width = cacheWidths[key];
    if (width) {
      return width;
    }
  }

  // Attempt to compute fetch the width of the SVG text element.
  try {
    width = textElement.getComputedTextLength();
  } catch (e) {
    // In other cases where we fail to get the computed text. Instead, use an
    // approximation and do not cache the result. At some later point in time
    // when the block is inserted into the visible DOM, this method will be
    // called again and, at that point in time, will not throw an exception.
    return textElement.textContent!.length * 8;
  }

  // Cache the computed width and return.
  if (cacheWidths) {
    cacheWidths[key] = width;
  }
  return width;
}

/**
 * Gets the width of a text element using a faster method than `getTextWidth`.
 * This method requires that we know the text element's font family and size in
 * advance. Similar to `getTextWidth`, we cache the width we compute.
 *
 * @param textElement An SVG 'text' element.
 * @param fontSize The font size to use.
 * @param fontWeight The font weight to use.
 * @param fontFamily The font family to use.
 * @returns Width of element.
 * @alias Blockly.utils.dom.getFastTextWidth
 */
export function getFastTextWidth(
    textElement: SVGTextElement, fontSize: number, fontWeight: string,
    fontFamily: string): number {
  return getFastTextWidthWithSizeString(
      textElement, fontSize + 'pt', fontWeight, fontFamily);
}

/**
 * Gets the width of a text element using a faster method than `getTextWidth`.
 * This method requires that we know the text element's font family and size in
 * advance. Similar to `getTextWidth`, we cache the width we compute.
 * This method is similar to `getFastTextWidth` but expects the font size
 * parameter to be a string.
 *
 * @param textElement An SVG 'text' element.
 * @param fontSize The font size to use.
 * @param fontWeight The font weight to use.
 * @param fontFamily The font family to use.
 * @returns Width of element.
 * @alias Blockly.utils.dom.getFastTextWidthWithSizeString
 */
export function getFastTextWidthWithSizeString(
    textElement: SVGTextElement, fontSize: string, fontWeight: string,
    fontFamily: string): number {
  const text = textElement.textContent;
  const key = text + '\n' + textElement.className.baseVal;
  let width;

  // Return the cached width if it exists.
  if (cacheWidths) {
    width = cacheWidths[key];
    if (width) {
      return width;
    }
  }

  if (!canvasContext) {
    // Inject the canvas element used for computing text widths.
    const computeCanvas = (document.createElement('canvas'));
    computeCanvas.className = 'blocklyComputeCanvas';
    document.body.appendChild(computeCanvas);

    // Initialize the HTML canvas context and set the font.
    // The context font must match blocklyText's fontsize and font-family
    // set in CSS.
    canvasContext = computeCanvas.getContext('2d') as CanvasRenderingContext2D;
  }
  // Set the desired font size and family.
  canvasContext.font = fontWeight + ' ' + fontSize + ' ' + fontFamily;

  // Measure the text width using the helper canvas context.
  if (text) {
    width = canvasContext.measureText(text).width;
  } else {
    width = 0;
  }

  // Cache the computed width and return.
  if (cacheWidths) {
    cacheWidths[key] = width;
  }
  return width;
}

/**
 * Measure a font's metrics. The height and baseline values.
 *
 * @param text Text to measure the font dimensions of.
 * @param fontSize The font size to use.
 * @param fontWeight The font weight to use.
 * @param fontFamily The font family to use.
 * @returns Font measurements.
 * @alias Blockly.utils.dom.measureFontMetrics
 */
export function measureFontMetrics(
    text: string, fontSize: string, fontWeight: string,
    fontFamily: string): {height: number, baseline: number} {
  const span = (document.createElement('span'));
  span.style.font = fontWeight + ' ' + fontSize + ' ' + fontFamily;
  span.textContent = text;

  const block = (document.createElement('div'));
  block.style.width = '1px';
  block.style.height = '0';

  const div = (document.createElement('div'));
  div.setAttribute('style', 'position: fixed; top: 0; left: 0; display: flex;');
  div.appendChild(span);
  div.appendChild(block);

  document.body.appendChild(div);
  const result = {
    height: 0,
    baseline: 0,
  };
  try {
    div.style.alignItems = 'baseline';
    result.baseline = block.offsetTop - span.offsetTop;
    div.style.alignItems = 'flex-end';
    result.height = block.offsetTop - span.offsetTop;
  } finally {
    document.body.removeChild(div);
  }
  return result;
}