import { useQuery } from "@tanstack/react-query";
import { useMemo } from "react";

import { api } from "@/services/api";

/** Dropdown-settings code holding the admin-managed IMPORT run numbers. */
export const IMPORT_TRAIN_NUMBERS_CODE = "import_train_numbers";

export interface ImportTrainNumberOption {
  value: string;
  label: string;
  disabled?: boolean;
}

/**
 * Selectable IMPORT run numbers for the Train Builder, sourced solely from the
 * admin-managed `import_train_numbers` dropdown setting — admins add and remove
 * runs from /dashboard/dropdown-settings and the pickers follow. There is no
 * hardcoded fallback on purpose: a missing setting must be visible (see
 * `settingMissing`) rather than masked by stale defaults.
 *
 * Numbers already claimed by an existing train are kept in the list but
 * disabled and tagged "in use". Pass `currentNumber` when editing a train so
 * its own number stays pickable, and so a legacy number that was removed from
 * the setting still renders.
 */
export function useImportTrainNumberOptions(currentNumber?: string | null) {
  const settingQuery = useQuery(
    api.dropdownSettings.getByCode.queryOptions({
      input: { code: IMPORT_TRAIN_NUMBERS_CODE },
      staleTime: 5 * 60_000,
      retry: false,
    }),
  );
  const usedQuery = useQuery(
    api.trainBuilder.usedTrainNumbers.queryOptions({ staleTime: 30_000 }),
  );

  const options = useMemo<ImportTrainNumberOption[]>(() => {
    const base = [...(settingQuery.data?.children ?? [])]
      .filter((option) => !option.disabled)
      .sort((a, b) => (a.order ?? 0) - (b.order ?? 0))
      .map((option) => ({
        value: option.value,
        label: option.label || option.value,
      }));

    const used = new Set(usedQuery.data?.importTrainNumbers ?? []);
    if (currentNumber) used.delete(currentNumber);

    const items: ImportTrainNumberOption[] = base.map((option) =>
      used.has(option.value)
        ? { ...option, label: `${option.label} — in use`, disabled: true }
        : option,
    );
    if (currentNumber && !items.some((option) => option.value === currentNumber)) {
      items.unshift({ value: currentNumber, label: currentNumber });
    }
    return items;
  }, [settingQuery.data, usedQuery.data, currentNumber]);

  const settingMissing = settingQuery.isError;

  return {
    options,
    isLoading: settingQuery.isLoading || usedQuery.isLoading,
    /** True when the dropdown setting is absent — surfaced instead of silently
     * falling back, so a broken config is visible rather than looking normal. */
    settingMissing,
    emptyMessage: settingMissing
      ? `Dropdown setting "${IMPORT_TRAIN_NUMBERS_CODE}" is missing — create it in Dropdown Settings`
      : "No free run numbers — add more in Dropdown Settings",
  };
}