// Sign-in: a person is an Ed25519 key (from their Theseus vault, or a key file
// on hosts without one). The gateway hands out a nonce, the client signs it,
// and gets a session token back. Only token hashes are stored.

import crypto from 'node:crypto';
import path from 'node:path';
import { readJson, writeJson } from './store.js';

const SPKI_ED25519 = Buffer.from('302a300506032b6570032100', 'hex');
const SESSION_DAYS = 90;

export const accountId = (pubkeyHex) => crypto.createHash('sha256').update(Buffer.from(pubkeyHex, 'hex')).digest('hex').slice(0, 32);

export function challengeText(publicUrl, nonce) {
  return `pithos-hosted-v1\n${publicUrl}\n${nonce}`;
}

export function verifyEd25519(pubkeyHex, message, signatureB64) {
  if (!/^[0-9a-f]{64}$/i.test(pubkeyHex || '')) return false;
  try {
    const key = crypto.createPublicKey({ key: Buffer.concat([SPKI_ED25519, Buffer.from(pubkeyHex, 'hex')]), format: 'der', type: 'spki' });
    return crypto.verify(null, Buffer.from(message, 'utf8'), key, Buffer.from(String(signatureB64 || ''), 'base64'));
  } catch { return false; }
}

export function createAuth(root) {
  const file = path.join(root, 'sessions.json');
  const nonces = new Map(); // nonce -> expiry
  const sessions = readJson(file, {});

  const hash = (t) => crypto.createHash('sha256').update(t).digest('hex');

  return {
    challenge() {
      const now = Date.now();
      for (const [n, exp] of nonces) if (exp < now) nonces.delete(n);
      if (nonces.size > 10_000) throw Object.assign(new Error('too many sign-ins in progress, try again shortly'), { status: 503 });
      const nonce = crypto.randomBytes(24).toString('base64url');
      nonces.set(nonce, now + 5 * 60_000);
      return nonce;
    },
    // Consumes the nonce whether or not the signature holds.
    takeNonce(nonce) {
      const exp = nonces.get(nonce);
      nonces.delete(nonce);
      return !!exp && exp > Date.now();
    },
    issue(id) {
      const token = crypto.randomBytes(32).toString('base64url');
      const now = Date.now();
      for (const [h, s] of Object.entries(sessions)) if (s.exp < now) delete sessions[h];
      sessions[hash(token)] = { id, exp: now + SESSION_DAYS * 86_400_000 };
      writeJson(file, sessions);
      return token;
    },
    lookup(token) {
      const s = token && sessions[hash(token)];
      return s && s.exp > Date.now() ? s.id : null;
    },
    revoke(token) {
      delete sessions[hash(token)];
      writeJson(file, sessions);
    },
  };
}