const WILDCARD_IPS = new Set(["", "0.0.0.0", "::"]);

/** IPv6 literals need brackets in a URL; location.hostname already has them. */
export function urlHost(host: string): string {
  return host.includes(":") && !host.startsWith("[") ? `[${host}]` : host;
}

function isIpLiteral(host: string): boolean {
  return /^\d{1,3}(\.\d{1,3}){3}$/.test(host) || host.startsWith("[");
}

/** Where a port bound to all interfaces is reached. The page's own hostname
 *  only works when it *is* the Docker host — behind a reverse proxy it is the
 *  proxy's domain, and domain:8080 lands on the proxy. So: the configured
 *  host, else the page's hostname when that is an IP (or localhost), else the
 *  host address the backend detected, else the page's hostname after all. */
export function defaultLinkHost(
  page: string,
  settings?: { port_link_host: string; detected_host_ip: string | null }
): string {
  if (settings?.port_link_host) return settings.port_link_host;
  if (isIpLiteral(page) || page === "localhost") return page;
  return settings?.detected_host_ip || page;
}

/** Pick the host to link to: an explicit override, the bound
 *  host IP if it's a concrete address, otherwise the default above. */
export function linkHost(hostIp: string | undefined, fallback: string, override?: string): string {
  if (override) return override;
  if (hostIp && !WILDCARD_IPS.has(hostIp)) return hostIp;
  return fallback;
}