/**

 * 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.

 */

/**

 * These variables store information about text content of a target node,

 * allowing comparison of content before and after a given event.

 *

 * Identify the node where selection currently begins, then observe

 * both its text content and its current position in the DOM. Since the

 * browser may natively replace the target node during composition, we can

 * use its position to find its replacement.

 *

 *

 */

let root = null;

let startText = null;

let fallbackText = null;

export function initialize(nativeEventTarget) {

  root = nativeEventTarget;

  startText = getText();

  return true;

}

export function reset() {

  root = null;

  startText = null;

  fallbackText = null;

}

export function getData() {

  if (fallbackText) {

    return fallbackText;

  }

  let start;

  const startValue = startText;

  const startLength = startValue.length;

  let end;

  const endValue = getText();

  const endLength = endValue.length;

  for (start = 0; start < startLength; start++) {

    if (startValue[start] !== endValue[start]) {

      break;

    }

  }

  const minEnd = startLength - start;

  for (end = 1; end <= minEnd; end++) {

    if (startValue[startLength - end] !== endValue[endLength - end]) {

      break;

    }

  }

  const sliceTail = end > 1 ? 1 - end : undefined;

  fallbackText = endValue.slice(start, sliceTail);

  return fallbackText;

}

export function getText() {

  if ('value' in root) {

    return root.value;

  }

  return root.textContent;

}