function base64urlEncode(buffer: ArrayBuffer): string {
  const bytes = new Uint8Array(buffer);
  let binary = '';
  for (let i = 0; i < bytes.length; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}

export function generateCodeVerifier(): string {
  const array = new Uint8Array(32);
  crypto.getRandomValues(array);
  return base64urlEncode(array.buffer);
}

export async function generateCodeChallenge(verifier: string): Promise<string> {
  const encoder = new TextEncoder();
  const data = encoder.encode(verifier);
  const digest = await crypto.subtle.digest('SHA-256', data);
  return base64urlEncode(digest);
}

export function generateState(): string {
  const array = new Uint8Array(32);
  crypto.getRandomValues(array);
  return base64urlEncode(array.buffer);
}