/*!
 * Copyright (c) 2019-present, Okta, Inc. and/or its affiliates. All rights reserved.
 * The Okta software accompanied by this notice is provided pursuant to the Apache License, Version 2.0 (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.
 *
 */

 /* eslint-disable complexity, max-statements */
import { stringToBase64Url, webcrypto } from '../../crypto';
import { MIN_VERIFIER_LENGTH, MAX_VERIFIER_LENGTH, DEFAULT_CODE_CHALLENGE_METHOD } from '../../constants';

function dec2hex (dec) {
  return ('0' + dec.toString(16)).substr(-2);
}

function getRandomString(length) {
  var a = new Uint8Array(Math.ceil(length / 2));
  webcrypto.getRandomValues(a);
  var str = Array.from(a, dec2hex).join('');
  return str.slice(0, length);
}

function generateVerifier(prefix?: string): string {
  var verifier = prefix || '';
  if (verifier.length < MIN_VERIFIER_LENGTH) {
    verifier = verifier + getRandomString(MIN_VERIFIER_LENGTH - verifier.length);
  }
  return encodeURIComponent(verifier).slice(0, MAX_VERIFIER_LENGTH);
}

function computeChallenge(str: string): PromiseLike<any> {  
  var buffer = new TextEncoder().encode(str);
  return webcrypto.subtle.digest('SHA-256', buffer).then(function(arrayBuffer) {
    var hash = String.fromCharCode.apply(null, new Uint8Array(arrayBuffer) as unknown as number[]);
    var b64u = stringToBase64Url(hash); // url-safe base64 variant
    return b64u;
  });
}

export default {
  DEFAULT_CODE_CHALLENGE_METHOD,
  generateVerifier,
  computeChallenge
};