function base64UrlEncode(buffer: ArrayBuffer) {
  const bytes = new Uint8Array(buffer)
  let binary = ""
  for (const b of bytes) {
    binary += String.fromCharCode(b)
  }
  return btoa(binary).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "")
}

export function randomString(byteLength = 32) {
  const bytes = new Uint8Array(byteLength)
  crypto.getRandomValues(bytes)
  return base64UrlEncode(bytes.buffer)
}

export async function sha256Base64Url(input: string) {
  const data = new TextEncoder().encode(input)
  const digest = await crypto.subtle.digest("SHA-256", data)
  return base64UrlEncode(digest)
}

export async function createPkcePair() {
  const verifier = randomString(32)
  const challenge = await sha256Base64Url(verifier)
  return { verifier, challenge }
}