/**
 * Copyright (c) Facebook, Inc. and its 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 getEventCharCode from './getEventCharCode';

/**
 * Normalization of deprecated HTML5 `key` values
 * @see https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent#Key_names
 */
const normalizeKey = {
  Esc: 'Escape',
  Spacebar: ' ',
  Left: 'ArrowLeft',
  Up: 'ArrowUp',
  Right: 'ArrowRight',
  Down: 'ArrowDown',
  Del: 'Delete',
  Win: 'OS',
  Menu: 'ContextMenu',
  Apps: 'ContextMenu',
  Scroll: 'ScrollLock',
  MozPrintableKey: 'Unidentified',
};

/**
 * Translation from legacy `keyCode` to HTML5 `key`
 * Only special keys supported, all others depend on keyboard layout or browser
 * @see https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent#Key_names
 */
const translateToKey = {
  '8': 'Backspace',
  '9': 'Tab',
  '12': 'Clear',
  '13': 'Enter',
  '16': 'Shift',
  '17': 'Control',
  '18': 'Alt',
  '19': 'Pause',
  '20': 'CapsLock',
  '27': 'Escape',
  '32': ' ',
  '33': 'PageUp',
  '34': 'PageDown',
  '35': 'End',
  '36': 'Home',
  '37': 'ArrowLeft',
  '38': 'ArrowUp',
  '39': 'ArrowRight',
  '40': 'ArrowDown',
  '45': 'Insert',
  '46': 'Delete',
  '112': 'F1',
  '113': 'F2',
  '114': 'F3',
  '115': 'F4',
  '116': 'F5',
  '117': 'F6',
  '118': 'F7',
  '119': 'F8',
  '120': 'F9',
  '121': 'F10',
  '122': 'F11',
  '123': 'F12',
  '144': 'NumLock',
  '145': 'ScrollLock',
  '224': 'Meta',
};

/**
 * @param {object} nativeEvent Native browser event.
 * @return {string} Normalized `key` property.
 */
function getEventKey(nativeEvent: KeyboardEvent): string {
  if (nativeEvent.key) {
    // Normalize inconsistent values reported by browsers due to
    // implementations of a working draft specification.

    // FireFox implements `key` but returns `MozPrintableKey` for all
    // printable characters (normalized to `Unidentified`), ignore it.
    const key = normalizeKey[nativeEvent.key] || nativeEvent.key;
    if (key !== 'Unidentified') {
      return key;
    }
  }

  // Browser does not implement `key`, polyfill as much of it as we can.
  if (nativeEvent.type === 'keypress') {
    const charCode = getEventCharCode(nativeEvent);

    // The enter-key is technically both printable and non-printable and can
    // thus be captured by `keypress`, no other non-printable key should.
    return charCode === 13 ? 'Enter' : String.fromCharCode(charCode);
  }
  if (nativeEvent.type === 'keydown' || nativeEvent.type === 'keyup') {
    // While user keyboard layout determines the actual meaning of each
    // `keyCode` value, almost all function keys have a universal value.
    return translateToKey[nativeEvent.keyCode] || 'Unidentified';
  }
  return '';
}

export default getEventKey;
