/**
 * @file avatar-url.js
 * @description Checks an avatar LINK the account typed (Settings → Account,
 * `POST /api/me/avatar/url`). The link is stored as it is and the avatar
 * routes redirect the viewer's browser to it — the server never downloads it,
 * so a picture behind the viewer's own login or on a company-internal host
 * (e.g. a Mattermost `/api/v4/users/<id>/image`) still shows. Held to:
 * `https://`, no userinfo, at most `MAX_LINK_LENGTH` characters, and no
 * loopback/private/link-local/reserved IP literal as the host (a link may not
 * aim every viewer's browser at their own machine or LAN).
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

const net = require("node:net");

const MAX_LINK_LENGTH = 2048;

const fail = (code, message) => Object.assign(new Error(message), { code });

const blocked = new net.BlockList();
for (const [addr, bits] of [
  ["0.0.0.0", 8],
  ["10.0.0.0", 8],
  ["100.64.0.0", 10],
  ["127.0.0.0", 8],
  ["169.254.0.0", 16],
  ["172.16.0.0", 12],
  ["192.0.0.0", 24],
  ["192.0.2.0", 24],
  ["192.88.99.0", 24],
  ["192.168.0.0", 16],
  ["198.18.0.0", 15],
  ["198.51.100.0", 24],
  ["203.0.113.0", 24],
  ["224.0.0.0", 4],
  ["240.0.0.0", 4],
]) {
  blocked.addSubnet(addr, bits, "ipv4");
}
for (const [addr, bits] of [
  ["::", 128],
  ["::1", 128],
  ["64:ff9b::", 96],
  ["64:ff9b:1::", 48],
  ["100::", 64],
  ["2001::", 23],
  ["2001:db8::", 32],
  ["2002::", 16],
  ["fc00::", 7],
  ["fe80::", 10],
  ["ff00::", 8],
]) {
  blocked.addSubnet(addr, bits, "ipv6");
}

/** True only for a globally routable unicast address. */
function isPublicAddress(address) {
  const family = net.isIP(address);
  if (family === 4) return !blocked.check(address, "ipv4");
  if (family !== 6) return false;
  const lower = address.toLowerCase();
  // An IPv4-mapped/compatible address is judged as the IPv4 address it carries.
  const mapped = /^::(?:ffff:)?(\d+\.\d+\.\d+\.\d+)$/.exec(lower);
  if (mapped) return isPublicAddress(mapped[1]);
  if (/^::(?:ffff:)?[0-9a-f]{1,4}:[0-9a-f]{1,4}$/.test(lower)) return false;
  // Only global unicast (2000::/3) is public.
  if (!/^[23][0-9a-f]{0,3}:/.test(lower)) return false;
  return !blocked.check(address, "ipv6");
}

/** The link, normalised, or EBADURL / EPRIVATEURL: https only, no userinfo, a real host. */
function parseAvatarUrl(text) {
  const raw = String(text ?? "").trim();
  if (raw.length > MAX_LINK_LENGTH) throw fail("EBADURL", "the link is too long");
  let url;
  try {
    url = new URL(raw);
  } catch {
    throw fail("EBADURL", "not a valid URL");
  }
  if (url.protocol !== "https:") throw fail("EBADURL", "only an https:// link");
  if (url.username || url.password) throw fail("EBADURL", "a link with a login is refused");
  if (!url.hostname) throw fail("EBADURL", "not a valid URL");
  const host = url.hostname.toLowerCase();
  const literal = host.replace(/^\[|\]$/g, "");
  if (
    host === "localhost" ||
    host.endsWith(".localhost") ||
    (net.isIP(literal) && !isPublicAddress(literal))
  ) {
    throw fail("EPRIVATEURL", "that address is not on the public internet");
  }
  return url.href;
}

module.exports = { MAX_LINK_LENGTH, isPublicAddress, parseAvatarUrl };