// v1.11.8: SSRF guard for web_fetch (and any other tool that follows a
// model-supplied URL). Sibling of path_guard.ts (workspace scope) and
// secret_guard.ts (filename deny) — same _guard.ts naming pattern. The
// spec suggested apps/server/src/services/safety/urlGuard.ts but BooCode
// has no `safety/` subdirectory and the existing guards live one level up.
//
// Block list, in order of evaluation:
//   - protocol other than http: / https:
//   - hostname is a known private name (localhost, 0.0.0.0, ::1)
//   - hostname ends with .local or .internal (mDNS / private TLD)
//   - IPv4 in any RFC1918 / loopback / CGNAT / link-local range
//
// IPv6 numeric literals aren't enumerated here. Most public hostnames
// resolve to IPv4 via DNS; an IPv6-only attack surface against a
// chat-app deployment is exotic enough to defer until a real abuse case
// motivates a comprehensive check. The protocol + name-suffix checks
// already cover the common LAN-targeting cases.

export interface UrlGuardResult {
  ok: boolean;
  reason?: string;
}

export function isPublicUrl(input: string): UrlGuardResult {
  let u: URL;
  try {
    u = new URL(input);
  } catch {
    return { ok: false, reason: 'invalid_url' };
  }

  if (u.protocol !== 'http:' && u.protocol !== 'https:') {
    return { ok: false, reason: `unsupported_protocol: ${u.protocol}` };
  }

  const host = u.hostname.toLowerCase();
  if (host.length === 0) {
    return { ok: false, reason: 'empty_host' };
  }

  // Bare-name targets
  if (host === 'localhost' || host === '0.0.0.0') {
    return { ok: false, reason: `private_host: ${host}` };
  }
  // node's URL strips the [] from a literal IPv6 host. Both forms checked.
  if (host === '::1' || host === '[::1]') {
    return { ok: false, reason: `loopback_v6: ${host}` };
  }

  // mDNS / private TLDs
  if (host.endsWith('.local') || host.endsWith('.internal')) {
    return { ok: false, reason: `private_suffix: ${host}` };
  }

  // IPv4 numeric ranges. Matches host that's all-numeric octets only — DNS
  // names that happen to start with digits (e.g. 1password.com) won't match.
  const ipv4 = host.match(/^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/);
  if (ipv4) {
    const o1 = Number(ipv4[1]);
    const o2 = Number(ipv4[2]);
    // Loopback 127.0.0.0/8
    if (o1 === 127) return { ok: false, reason: `loopback: ${host}` };
    // RFC1918 10.0.0.0/8
    if (o1 === 10) return { ok: false, reason: `rfc1918: ${host}` };
    // RFC1918 172.16.0.0/12
    if (o1 === 172 && o2 >= 16 && o2 <= 31) return { ok: false, reason: `rfc1918: ${host}` };
    // RFC1918 192.168.0.0/16
    if (o1 === 192 && o2 === 168) return { ok: false, reason: `rfc1918: ${host}` };
    // CGNAT / Tailscale 100.64.0.0/10
    if (o1 === 100 && o2 >= 64 && o2 <= 127) return { ok: false, reason: `cgnat: ${host}` };
    // Link-local 169.254.0.0/16 (covers AWS/GCP metadata IMDS)
    if (o1 === 169 && o2 === 254) return { ok: false, reason: `link_local: ${host}` };
    // Source net 0.0.0.0/8 (rare but possible)
    if (o1 === 0) return { ok: false, reason: `zero_net: ${host}` };
  }

  return { ok: true };
}