import { environment } from "../environments/environment";

const FHIR_ID = /^[A-Za-z0-9\-.]{1,64}$/;
const LOCAL_BASES = [environment.fhirClinicalApi, environment.fhirBaseApi];

const pathUnder = (reference: string, bases: readonly string[]): string | undefined => {
  let url: URL;
  try {
    url = new URL(reference);
  } catch {
    return undefined;
  }
  if (url.search || url.hash || url.username || url.password) return undefined;
  const full = url.origin + url.pathname;
  for (const base of bases) {
    const root = new URL(base);
    const prefix = root.origin + root.pathname.replace(/\/+$/, "") + "/";
    if (full.startsWith(prefix)) return full.slice(prefix.length);
  }
  return undefined;
};

// The id a reference names only when it is the current version of a `type` resource: `Type/id`, or an absolute url
// under one of this deployment's own FHIR bases. Another server's url, and versioned, contained or queried forms, name nothing.
export const referencedId = (reference: string | undefined, type: string, localBases: readonly string[] = LOCAL_BASES): string | undefined => {
  if (typeof reference !== "string" || !reference) return undefined;
  const absolute = /^[A-Za-z][A-Za-z0-9+.-]*:/.test(reference);
  if (!absolute && (reference.includes("?") || reference.includes("#"))) return undefined;
  const path = absolute ? pathUnder(reference, localBases) : reference;
  const parts = path?.split("/") ?? [];
  return parts.length === 2 && parts[0] === type && FHIR_ID.test(parts[1]) ? parts[1] : undefined;
};