// SSRF guard: block internal/private/metadata targets for server-side fetch.

const BLOCKED_HOSTNAMES = new Set(["localhost", "ip6-localhost", "ip6-loopback"]);
const BLOCKED_SUFFIXES = [".internal", ".local", ".localhost"];

// Parse dotted IPv4 to 32-bit integer, or null if not a valid IPv4 literal.
function ipv4ToInt(host) {
  const parts = host.split(".");
  if (parts.length !== 4) return null;
  let value = 0;
  for (const part of parts) {
    if (!/^\d{1,3}$/.test(part)) return null;
    const octet = Number(part);
    if (octet > 255) return null;
    value = value * 256 + octet;
  }
  return value >>> 0;
}

// Private/reserved IPv4 ranges as [startInt, maskBits].
const BLOCKED_V4_RANGES = [
  [ipv4ToInt("0.0.0.0"), 8],
  [ipv4ToInt("10.0.0.0"), 8],
  [ipv4ToInt("127.0.0.0"), 8],
  [ipv4ToInt("169.254.0.0"), 16],
  [ipv4ToInt("172.16.0.0"), 12],
  [ipv4ToInt("192.168.0.0"), 16],
];

function isBlockedIpv4(host) {
  const ip = ipv4ToInt(host);
  if (ip === null) return false;
  return BLOCKED_V4_RANGES.some(([base, bits]) => {
    const mask = bits === 0 ? 0 : (0xffffffff << (32 - bits)) >>> 0;
    return (ip & mask) === (base & mask);
  });
}

function isBlockedIpv6(host) {
  const h = host.replace(/^\[|\]$/g, "").toLowerCase();
  if (h === "::1" || h === "::") return true;
  return h.startsWith("fe80:") || h.startsWith("fc") || h.startsWith("fd");
}

// Throw if URL targets a non-public host. Caller should map to 400.
export function assertPublicUrl(rawUrl) {
  const parsed = new URL(rawUrl);
  const host = parsed.hostname.toLowerCase();

  if (BLOCKED_HOSTNAMES.has(host)) throw new Error("Blocked URL: internal host");
  if (BLOCKED_SUFFIXES.some((s) => host.endsWith(s))) throw new Error("Blocked URL: internal host");
  if (isBlockedIpv4(host)) throw new Error("Blocked URL: private IP");
  if (host.includes(":") && isBlockedIpv6(host)) throw new Error("Blocked URL: private IP");
}