// Browser WebAuthn and secret encryption helpers. The host verifies every proof.
const bytes = text => Uint8Array.from(atob(text.replace(/-/g, '+').replace(/_/g, '/')), c => c.charCodeAt(0));
const encoded = buffer => btoa(String.fromCharCode(...new Uint8Array(buffer))).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
const post = async (path, body) => {
  const response = await fetch('/api/' + path.replace(/^\//, ''), {method: 'POST', headers: {'content-type': 'application/json'}, body: JSON.stringify(body)});
  const result = await response.json();
  if (!response.ok) throw new Error(result.message);
  return result;
};
function options(challenge) {
  const value = challenge.options;
  value.publicKey.challenge = bytes(value.publicKey.challenge);
  if (value.publicKey.user) value.publicKey.user.id = bytes(value.publicKey.user.id);
  for (const key of ['allowCredentials', 'excludeCredentials']) {
    for (const credential of value.publicKey[key] || []) credential.id = bytes(credential.id);
  }
  return value;
}
function serialize(credential) {
  const response = {};
  for (const key of ['clientDataJSON', 'attestationObject', 'authenticatorData', 'signature', 'userHandle']) {
    if (credential.response[key]) response[key] = encoded(credential.response[key]);
  }
  return {id: credential.id, rawId: encoded(credential.rawId), type: credential.type, response, clientExtensionResults: credential.getClientExtensionResults()};
}
async function assertion(challenge) {
  return {challenge_id: challenge.id, assertion: serialize(await navigator.credentials.get(options(challenge)))};
}
async function encrypt(publicKey, secret) {
  const host = await crypto.subtle.importKey('raw', new Uint8Array(publicKey), {name: 'ECDH', namedCurve: 'P-256'}, false, []);
  const pair = await crypto.subtle.generateKey({name: 'ECDH', namedCurve: 'P-256'}, true, ['deriveBits']);
  const shared = await crypto.subtle.deriveBits({name: 'ECDH', public: host}, pair.privateKey, 256);
  const material = await crypto.subtle.importKey('raw', shared, 'HKDF', false, ['deriveKey']);
  const key = await crypto.subtle.deriveKey({name: 'HKDF', hash: 'SHA-256', salt: new Uint8Array(), info: new TextEncoder().encode('sausage/secret-entry/v1')}, material, {name: 'AES-GCM', length: 256}, false, ['encrypt']);
  const iv = crypto.getRandomValues(new Uint8Array(12));
  const ciphertext = await crypto.subtle.encrypt({name: 'AES-GCM', iv}, key, new TextEncoder().encode(secret));
  const ephemeral_public_key = new Uint8Array(await crypto.subtle.exportKey('raw', pair.publicKey));
  const envelope = {ephemeral_public_key: [...ephemeral_public_key], iv: [...iv], ciphertext: [...new Uint8Array(ciphertext)]};
  const hash = new Uint8Array(await crypto.subtle.digest('SHA-256', new Uint8Array([...envelope.ephemeral_public_key, ...envelope.iv, ...envelope.ciphertext])));
  return {envelope, ciphertext_sha256: [...hash].map(byte => byte.toString(16).padStart(2, '0')).join('')};
}