import { compareText } from "./collate";
import { serverOrderLang } from "./saveLanguage";

// The channel manager's list order, and the priority steps its menu offers.

/** The steps a channel's menu offers (owner, 2026-09-26): fixed levels, so bubbling a channel up
 *  the list is one pick, not a run of +1 presses, and not straight to the top either. The row's
 *  stepper still sets any value, negatives included. */
const PRIORITY_STEPS: readonly number[] = [10, 5, 3, 2, 1, 0];

/** The steps to offer for a channel at `current`: the fixed ones, plus `current` itself in its
 *  place when it is off the scale (a 7, a -2) — the menu always shows, ticked, where it is now. */
export function priorityChoices(current: number): number[] {
  return PRIORITY_STEPS.includes(current)
    ? [...PRIORITY_STEPS]
    : [...PRIORITY_STEPS, current].sort((a, b) => b - a);
}

interface Ordered {
  id: string;
  priority: number;
  title?: string | null;
}

/** The server's order (`routes/channels.py`: priority desc, then the title in the reader's alphabet —
 *  the ICU collation of `app/collation.py`, which `compareText` shares — a missing title last). */
function before(a: Ordered, b: Ordered, lang: string): boolean {
  if (a.priority !== b.priority) return a.priority > b.priority;
  if (a.title == null) return false;
  if (b.title == null) return true;
  return compareText(a.title, b.title, lang) < 0;
}

/** `rows` with the channel `id` taken out and put back where its priority now places it, every
 *  other row left exactly where it was — the server's order, without a refetch that would reorder
 *  anything the reader did not touch. It takes the account's `preferences`, not a language: the
 *  server sorts in the STORED language (`serverOrderLang`), which a UI language is not always. */
export function placeByPriority<T extends Ordered>(
  rows: readonly T[],
  id: string,
  preferences: Record<string, unknown> | null | undefined,
): T[] {
  const moved = rows.find((r) => r.id === id);
  if (!moved) return [...rows];
  const lang = serverOrderLang(preferences);
  const rest = rows.filter((r) => r !== moved);
  const at = rest.findIndex((r) => before(moved, r, lang));
  rest.splice(at < 0 ? rest.length : at, 0, moved);
  return rest;
}