offset-key.js

/**
 * Offset key parser regex.
 */

const PARSER = /^(\w+)(?:-(\d+))?$/

/**
 * Offset key attribute name.
 */

const ATTRIBUTE = 'data-offset-key'
const SELECTOR = `[${ATTRIBUTE}]`

/**
 * Find the start and end bounds from an `offsetKey` and `ranges`.
 *
 * @param {Number} index
 * @param {List} ranges
 * @return {Object}
 */

function findBounds(index, ranges) {
  const range = ranges.get(index)
  const start = ranges
    .slice(0, index)
    .reduce((memo, r) => {
      return memo += r.text.length
    }, 0)

  return {
    start,
    end: start + range.text.length
  }
}

/**
 * From a `element`, find the closest parent's offset key.
 *
 * @param {Element} element
 * @param {Number} offset
 * @return {Object}
 */

function findKey(element, offset) {
  if (element.nodeType == 3) element = element.parentNode

  const parent = element.closest(SELECTOR)
  const children = element.querySelectorAll(SELECTOR)
  let offsetKey

  // Get the key from a parent if one exists.
  if (parent) {
    offsetKey = parent.getAttribute(ATTRIBUTE)
  }

  // COMPAT: In Firefox, and potentially other browsers, when performing a
  // "select all" action, a parent element is selected instead of the text. In
  // this case, we need to select the proper inner text nodes. (2016/07/26)
  else if (children.length) {
    let child = children[0]

    if (offset != 0) {
      child = children[children.length - 1]
      offset = child.textContent.length
    }

    offsetKey = child.getAttribute(ATTRIBUTE)
  }

  // Otherwise, for void node scenarios, a cousin element will be selected, and
  // we need to select the first text node cousin we can find.
  else {
    while (element = element.parentNode) {
      const cousin = element.querySelector(SELECTOR)
      if (!cousin) continue
      offsetKey = cousin.getAttribute(ATTRIBUTE)
      offset = cousin.textContent.length
      break
    }
  }

  // If we still didn't find an offset key, error. This is a bug.
  if (!offsetKey) {
    throw new Error(`Unable to find offset key for ${element} with offset "${offset}".`)
  }

  // Parse the offset key.
  const parsed = parse(offsetKey)

  return {
    key: parsed.key,
    index: parsed.index,
    offset
  }
}

/**
 * Find the selection point from an `offsetKey` and `ranges`.
 *
 * @param {Object} offsetKey
 * @param {List} ranges
 * @return {Object}
 */

function findPoint(offsetKey, ranges) {
  let { key, index, offset } = offsetKey
  const { start, end } = findBounds(index, ranges)

  // Don't let the offset be outside of the start and end bounds.
  offset = start + offset
  offset = Math.max(offset, start)
  offset = Math.min(offset, end)

  return {
    key,
    index,
    start,
    end,
    offset
  }
}

/**
 * Parse an offset key `string`.
 *
 * @param {String} string
 * @return {Object}
 */

function parse(string) {
  const matches = PARSER.exec(string)
  if (!matches) throw new Error(`Invalid offset key string "${string}".`)
  const [ original, key, index ] = matches
  return {
    key,
    index: parseInt(index, 10)
  }
}

/**
 * Stringify an offset key `object`.
 *
 * @param {Object} object
 *   @property {String} key
 *   @property {Number} index
 * @return {String}
 */

function stringify(object) {
  return `${object.key}-${object.index}`
}

/**
 * Export.
 */

export default {
  findBounds,
  findKey,
  findPoint,
  parse,
  stringify
}