polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-annotation.js

/**
 * @license
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the 'License');
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an 'AS IS' BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// TODO(wyatta): refactor this to be <MARK> rather than <HL>.
const ANNOTATION_TAG = 'HL';

// Astral code point as per https://mathiasbynens.be/notes/javascript-unicode
const REGEX_ASTRAL_SYMBOL = /[\uD800-\uDBFF][\uDC00-\uDFFF]/;

export const GrAnnotation = {

  /**
   * The DOM API textContent.length calculation is broken when the text
   * contains Unicode. See https://mathiasbynens.be/notes/javascript-unicode .
   *
   * @param  {!Text} node text node.
   * @return {number} The length of the text.
   */
  getLength(node) {
    return this.getStringLength(node.textContent);
  },

  getStringLength(str) {
    return str.replace(REGEX_ASTRAL_SYMBOL, '_').length;
  },

  /**
   * Annotates the [offset, offset+length) text segment in the parent with the
   * element definition provided as arguments.
   *
   * @param {!Element} parent the node whose contents will be annotated.
   * @param {number} offset the 0-based offset from which the annotation will
   *   start.
   * @param {number} length of the annotated text.
   * @param {GrAnnotation.ElementSpec} elementSpec the spec to create the
   *   annotating element.
   */
  annotateWithElement(parent, offset, length, {tagName, attributes = {}}) {
    let childNodes;

    if (parent instanceof Element) {
      childNodes = Array.from(parent.childNodes);
    } else if (parent instanceof Text) {
      childNodes = [parent];
      parent = parent.parentNode;
    } else {
      return;
    }

    const nestedNodes = [];
    for (let node of childNodes) {
      const initialNodeLength = this.getLength(node);
      // If the current node is completely before the offset.
      if (offset > 0 && initialNodeLength <= offset) {
        offset -= initialNodeLength;
        continue;
      }

      if (offset > 0) {
        node = this.splitNode(node, offset);
        offset = 0;
      }
      if (this.getLength(node) > length) {
        this.splitNode(node, length);
      }
      nestedNodes.push(node);

      length -= this.getLength(node);
      if (!length) break;
    }

    const wrapper = document.createElement(tagName);
    const sanitizer = window.Polymer.sanitizeDOMValue;
    for (const [name, value] of Object.entries(attributes)) {
      wrapper.setAttribute(
          name, sanitizer ?
            sanitizer(value, name, 'attribute', wrapper) :
            value);
    }
    for (const inner of nestedNodes) {
      parent.replaceChild(wrapper, inner);
      wrapper.appendChild(inner);
    }
  },

  /**
   * Surrounds the element's text at specified range in an ANNOTATION_TAG
   * element. If the element has child elements, the range is split and
   * applied as deeply as possible.
   */
  annotateElement(parent, offset, length, cssClass) {
    const nodes = [].slice.apply(parent.childNodes);
    let nodeLength;
    let subLength;

    for (const node of nodes) {
      nodeLength = this.getLength(node);

      // If the current node is completely before the offset.
      if (nodeLength <= offset) {
        offset -= nodeLength;
        continue;
      }

      // Sublength is the annotation length for the current node.
      subLength = Math.min(length, nodeLength - offset);

      if (node instanceof Text) {
        this._annotateText(node, offset, subLength, cssClass);
      } else if (node instanceof HTMLElement) {
        this.annotateElement(node, offset, subLength, cssClass);
      }

      // If there is still more to annotate, then shift the indices, otherwise
      // work is done, so break the loop.
      if (subLength < length) {
        length -= subLength;
        offset = 0;
      } else {
        break;
      }
    }
  },

  /**
   * Wraps node in annotation tag with cssClass, replacing the node in DOM.
   *
   * @return {!Element} Wrapped node.
   */
  wrapInHighlight(node, cssClass) {
    let hl;
    if (node.tagName === ANNOTATION_TAG) {
      hl = node;
      hl.classList.add(cssClass);
    } else {
      hl = document.createElement(ANNOTATION_TAG);
      hl.className = cssClass;
      Polymer.dom(node.parentElement).replaceChild(hl, node);
      Polymer.dom(hl).appendChild(node);
    }
    return hl;
  },

  /**
   * Splits Text Node and wraps it in hl with cssClass.
   * Wraps trailing part after split, tailing one if opt_firstPart is true.
   *
   * @param {!Node} node
   * @param {number} offset
   * @param {string} cssClass
   * @param {boolean=} opt_firstPart
   */
  splitAndWrapInHighlight(node, offset, cssClass, opt_firstPart) {
    if (this.getLength(node) === offset || offset === 0) {
      return this.wrapInHighlight(node, cssClass);
    } else {
      if (opt_firstPart) {
        this.splitNode(node, offset);
        // Node points to first part of the Text, second one is sibling.
      } else {
        node = this.splitNode(node, offset);
      }
      return this.wrapInHighlight(node, cssClass);
    }
  },

  /**
   * Splits Node at offset.
   * If Node is Element, it's cloned and the node at offset is split too.
   *
   * @param {!Node} node
   * @param {number} offset
   * @return {!Node} Trailing Node.
   */
  splitNode(element, offset) {
    if (element instanceof Text) {
      return this.splitTextNode(element, offset);
    }
    const tail = element.cloneNode(false);
    element.parentElement.insertBefore(tail, element.nextSibling);
    // Skip nodes before offset.
    let node = element.firstChild;
    while (node &&
        this.getLength(node) <= offset ||
        this.getLength(node) === 0) {
      offset -= this.getLength(node);
      node = node.nextSibling;
    }
    if (this.getLength(node) > offset) {
      tail.appendChild(this.splitNode(node, offset));
    }
    while (node.nextSibling) {
      tail.appendChild(node.nextSibling);
    }
    return tail;
  },

  /**
   * Node.prototype.splitText Unicode-valid alternative.
   *
   * DOM Api for splitText() is broken for Unicode:
   * https://mathiasbynens.be/notes/javascript-unicode
   *
   * @param {!Text} node
   * @param {number} offset
   * @return {!Text} Trailing Text Node.
   */
  splitTextNode(node, offset) {
    if (node.textContent.match(REGEX_ASTRAL_SYMBOL)) {
      // TODO (viktard): Polyfill Array.from for IE10.
      const head = Array.from(node.textContent);
      const tail = head.splice(offset);
      const parent = node.parentNode;

      // Split the content of the original node.
      node.textContent = head.join('');

      const tailNode = document.createTextNode(tail.join(''));
      if (parent) {
        parent.insertBefore(tailNode, node.nextSibling);
      }
      return tailNode;
    } else {
      return node.splitText(offset);
    }
  },

  _annotateText(node, offset, length, cssClass) {
    const nodeLength = this.getLength(node);

    // There are four cases:
    //  1) Entire node is highlighted.
    //  2) Highlight is at the start.
    //  3) Highlight is at the end.
    //  4) Highlight is in the middle.

    if (offset === 0 && nodeLength === length) {
      // Case 1.
      this.wrapInHighlight(node, cssClass);
    } else if (offset === 0) {
      // Case 2.
      this.splitAndWrapInHighlight(node, length, cssClass, true);
    } else if (offset + length === nodeLength) {
      // Case 3
      this.splitAndWrapInHighlight(node, offset, cssClass, false);
    } else {
      // Case 4
      this.splitAndWrapInHighlight(this.splitTextNode(node, offset), length,
          cssClass, true);
    }
  },
};

/**
 * Data used to construct an element.
 *
 * @typedef {{
 *   tagName: string,
 *   attributes: (!Object<string, *>|undefined)
 * }}
 */
GrAnnotation.ElementSpec;