/**

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 *

 * @flow

 */

import {TEXT_NODE} from './HTMLNodeType';

/**

 * Given any node return the first leaf node without children.

 *

 * @param {DOMElement|DOMTextNode} node

 * @return {DOMElement|DOMTextNode}

 */

function getLeafNode(node: ?(Node | Element)) {

  while (node && node.firstChild) {

    node = node.firstChild;

  }

  return node;

}

/**

 * Get the next sibling within a container. This will walk up the

 * DOM if a node's siblings have been exhausted.

 *

 * @param {DOMElement|DOMTextNode} node

 * @return {?DOMElement|DOMTextNode}

 */

function getSiblingNode(node: ?(Node | Element)) {

  while (node) {

    if (node.nextSibling) {

      return node.nextSibling;

    }

    node = node.parentNode;

  }

}

/**

 * Get object describing the nodes which contain characters at offset.

 *

 * @param {DOMElement|DOMTextNode} root

 * @param {number} offset

 * @return {?object}

 */

function getNodeForCharacterOffset(root: Element, offset: number): ?Object {

  let node = getLeafNode(root);

  let nodeStart = 0;

  let nodeEnd = 0;

  while (node) {

    if (node.nodeType === TEXT_NODE) {

      nodeEnd = nodeStart + node.textContent.length;

      if (nodeStart <= offset && nodeEnd >= offset) {

        return {

          node: node,

          offset: offset - nodeStart,

        };

      }

      nodeStart = nodeEnd;

    }

    node = getLeafNode(getSiblingNode(node));

  }

}

export default getNodeForCharacterOffset;