upfront-editable/lib/util/binary_search.js

Friendly contenteditable API

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.binaryCursorSearch = binaryCursorSearch;

var _element = require("./element");

/**
 * This is a binary search algorithm implementation aimed at finding
 * a character offset position in a consecutive strings of characters
 * over several lines.
 *
 * Refer to this page in order to learn more about binary search:
 * https://en.wikipedia.org/wiki/Binary_search_algorithm
 *
 * @returns {object}
 *  - object with boolean `wasFound` indicating if the binary search found an offset and `offset` to indicate the actual character offset
 */
function binaryCursorSearch(_ref) {
  var host = _ref.host,
      requiredOnFirstLine = _ref.requiredOnFirstLine,
      requiredOnLastLine = _ref.requiredOnLastLine,
      positionX = _ref.positionX;
  var hostRange = host.ownerDocument.createRange();
  hostRange.selectNodeContents(host);
  var hostCoords = hostRange.getBoundingClientRect();
  var totalCharCount = (0, _element.getTotalCharCount)(host);
  var textNodes = (0, _element.textNodesUnder)(host); // early terminate on empty editables

  if (totalCharCount === 0) return {
    wasFound: false
  };
  var data = {
    currentOffset: Math.floor(totalCharCount / 2),
    leftLimit: 0,
    rightLimit: totalCharCount
  };
  var offset = data.currentOffset;
  var distance;
  var safety = 20;

  while (data.leftLimit < data.rightLimit && safety > 0) {
    safety = safety -= 1;
    offset = data.currentOffset;

    var _range = createRangeAtCharacterOffset({
      textNodes: textNodes,
      offset: data.currentOffset
    });

    var _coords = _range.getBoundingClientRect();

    distance = Math.abs(_coords.left - positionX); // up / down axis

    if (requiredOnFirstLine && hostCoords.top !== _coords.top) {
      moveLeft(data);
      continue;
    } else if (requiredOnLastLine && hostCoords.bottom !== _coords.bottom) {
      moveRight(data);
      continue;
    } // left / right axis


    if (positionX < _coords.left) {
      moveLeft(data);
    } else {
      moveRight(data);
    }
  }

  var range = createRangeAtCharacterOffset({
    textNodes: textNodes,
    offset: data.currentOffset
  });
  var coords = range.getBoundingClientRect();
  var finalDistance = Math.abs(coords.left - positionX); // Decide if last or second last offset is closest

  if (finalDistance < distance) {
    distance = finalDistance;
    offset = data.currentOffset;
  }

  return {
    distance: distance,
    offset: offset,
    wasFound: true
  };
} // move the binary search index in between the current position and the left limit


function moveLeft(data) {
  data.rightLimit = data.currentOffset;
  data.currentOffset = Math.floor((data.currentOffset + data.leftLimit) / 2);
} // move the binary search index in between the current position and the right limit


function moveRight(data) {
  data.leftLimit = data.currentOffset;
  data.currentOffset = Math.ceil((data.currentOffset + data.rightLimit) / 2);
}

function createRangeAtCharacterOffset(_ref2) {
  var textNodes = _ref2.textNodes,
      offset = _ref2.offset;

  var _getTextNodeAndRelati = (0, _element.getTextNodeAndRelativeOffset)({
    textNodes: textNodes,
    absOffset: offset
  }),
      node = _getTextNodeAndRelati.node,
      relativeOffset = _getTextNodeAndRelati.relativeOffset;

  var newRange = node.ownerDocument.createRange();
  newRange.setStart(node, relativeOffset);
  newRange.collapse(true);
  return newRange;
}