import { useEffect, useState } from "react";

import { api } from "../api/client";
import type { Catalog, MedsReference } from "../api/types";

/*
 * Static reference data from the server (questionnaire catalog, drug reference): fetched once per app run and
 * shared by every screen. A failed fetch is retried on the next mount; screens work without it, only less rich.
 */

function cached<T>(load: () => Promise<T>) {
  let value: T | null = null;
  let inflight: Promise<T> | null = null;
  const get = () => {
    inflight ??= load().then(
      (v) => (value = v),
      (e) => {
        inflight = null;
        throw e;
      },
    );
    return inflight;
  };
  return function useCached(): T | null {
    const [v, setV] = useState<T | null>(value);
    useEffect(() => {
      if (value) return;
      let alive = true;
      get()
        .then((x) => alive && setV(x))
        .catch(() => undefined);
      return () => {
        alive = false;
      };
    }, []);
    return v;
  };
}

export const useCatalog = cached<Catalog>(api.catalog);
export const useMedsReference = cached<MedsReference>(api.medsReference);