/**
 * Copyright 2013-2014 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule getEventKey
 * @typechecks static-only
 */

"use strict";

var invariant = require('invariant');

/**
 * Normalization of deprecated HTML5 `key` values
 * @see https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent#Key_names
 */
var 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 `which`/`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
 */
var 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) {
  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.
    var 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') {
    // Create the character from the `charCode` ourselves and use as an almost
    // perfect replacement.
    var charCode = 'charCode' in nativeEvent ?
      nativeEvent.charCode :
      nativeEvent.keyCode;

    // 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';
  }

  invariant(false, "Unexpected keyboard event type: %s", nativeEvent.type);
}

module.exports = getEventKey;
