"use client";

import { useEffect, useState } from "react";
import { useQuery } from "@tanstack/react-query";
import { useConnectivity } from "@/lib/offline/connectivity";
import { fetchTreatmentPrefill } from "./api";
import type { TreatmentPrefill } from "./types";

const DEBOUNCE_MS = 500;
const MIN_PRODUCT_LENGTH = 2;
const MAX_PRODUCT_LENGTH = 200;

/**
 * The beekeeper's own last values for the product typed so far. Waits until
 * typing pauses, needs at least two characters and asks only while online -
 * a prefill is a convenience, never a reason to block or queue anything.
 * While a request for the same product is pending or the device is offline,
 * the last answer for that product stays; for any other product it is dropped.
 */
export function useTreatmentPrefill(product: string): TreatmentPrefill | null {
  const trimmed = product.trim();
  const [debounced, setDebounced] = useState("");
  const connectivity = useConnectivity();

  useEffect(() => {
    const timer = setTimeout(() => setDebounced(trimmed), DEBOUNCE_MS);
    return () => clearTimeout(timer);
  }, [trimmed]);

  const isSettled = debounced === trimmed;
  const isAskable =
    trimmed.length >= MIN_PRODUCT_LENGTH && trimmed.length <= MAX_PRODUCT_LENGTH;
  const enabled = connectivity === "online" && isSettled && isAskable;
  const { data } = useQuery({
    queryKey: ["treatments", "prefill", debounced],
    queryFn: () => fetchTreatmentPrefill(debounced),
    enabled,
  });

  // The last settled answer is kept only for the product it was fetched for
  // (pending request, offline). Once the product differs it is dropped at
  // once, so a failed request can never leave another product's values.
  const [held, setHeld] = useState<{ product: string; prefill: TreatmentPrefill | null } | null>(
    null,
  );
  let settled: TreatmentPrefill | null | undefined;
  if (isSettled && !isAskable) settled = null;
  else if (enabled) settled = data;
  if (settled !== undefined && (held?.product !== trimmed || held.prefill !== settled)) {
    setHeld({ product: trimmed, prefill: settled });
  }
  if (settled !== undefined) return settled;
  return held?.product === trimmed ? held.prefill : null;
}