ui/src/frontend/keyboard_layout_map.ts

// Copyright (C) 2023 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
//
//      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.

// A keyboard layout map that converts key codes to their equivalent glyphs for
// a given keyboard layout (e.g. 'KeyX' -> 'x').
export interface KeyboardLayoutMap {
  get(code: string): string | undefined;
}

interface Keyboard {
  getLayoutMap(): KeyboardLayoutMap;
}

export class NotSupportedError extends Error {}

// Fetch the user's keyboard layout map.
// This function is merely a wrapper around the keyboard API, which throws a
// specific error when used in browsers that don't support it.
export async function nativeKeyboardLayoutMap(): Promise<KeyboardLayoutMap> {
  // Browser's that don't support the Keyboard API won't have a keyboard
  // property in their window.navigator object.
  // Note: it seems this is also what Chrome does when the website is accessed
  // through an insecure connection.
  if ('keyboard' in window.navigator) {
    // Typescript's dom library doesn't know about this feature, so we must
    // take some liberties when it comes to relaxing types
    const keyboard = window.navigator.keyboard as Keyboard;
    return await keyboard.getLayoutMap();
  } else {
    throw new NotSupportedError('Keyboard API is not supported');
  }
}