/**
 * Convert from a Base64URL-encoded string to an Array Buffer. Best used when converting a
 * credential ID from a JSON string to an ArrayBuffer, like in allowCredentials or
 * excludeCredentials
 *
 * Helper method to compliment `bufferToBase64URLString`
 */
export function base64URLStringToBuffer(base64URLString: string): ArrayBuffer {
  // Convert from Base64URL to Base64
  const base64 = base64URLString.replace(/-/g, '+').replace(/_/g, '/');
  /**
   * Pad with '=' until it's a multiple of four
   * (4 - (85 % 4 = 1) = 3) % 4 = 3 padding
   * (4 - (86 % 4 = 2) = 2) % 4 = 2 padding
   * (4 - (87 % 4 = 3) = 1) % 4 = 1 padding
   * (4 - (88 % 4 = 0) = 4) % 4 = 0 padding
   */
  const padLength = (4 - (base64.length % 4)) % 4;
  const padded = base64.padEnd(base64.length + padLength, '=');

  // Convert to a binary string
  const binary = atob(padded);

  // Convert binary string to buffer
  const buffer = new ArrayBuffer(binary.length);
  const bytes = new Uint8Array(buffer);

  for (let i = 0; i < binary.length; i++) {
    bytes[i] = binary.charCodeAt(i);
  }

  return buffer;
}