// DataTable groupBy 的纯逻辑:按键分组(保持首次出现顺序或自定义顺序)与展开态持久化。

export type RowGroup<T> = { key: string; rows: T[] };

/** 按 key 分组;缺省按首次出现顺序,给 order 时按 order 排组(组内保持原顺序) */
export function groupRows<T>(
  rows: readonly T[],
  keyOf: (row: T) => string,
  order?: (a: string, b: string) => number,
): RowGroup<T>[] {
  const map = new Map<string, T[]>();
  for (const r of rows) {
    const k = keyOf(r);
    const list = map.get(k);
    if (list) list.push(r);
    else map.set(k, [r]);
  }
  const groups = [...map].map(([key, rs]) => ({ key, rows: rs }));
  return order ? groups.sort((a, b) => order(a.key, b.key)) : groups;
}

const PREFIX = "umt.table-groups:";
type Store = Pick<Storage, "getItem" | "setItem">;
const defaultStore = (): Store | undefined => globalThis.localStorage;

/** 读折叠的组(localStorage 不可用或内容损坏时为 null,由调用方取缺省) */
export function readCollapsed(storageKey: string | undefined, store = defaultStore): Set<string> | null {
  if (!storageKey) return null;
  try {
    const raw = store()?.getItem(PREFIX + storageKey);
    if (!raw) return null;
    const v = JSON.parse(raw) as unknown;
    return Array.isArray(v) ? new Set(v.filter((x): x is string => typeof x === "string")) : null;
  } catch {
    return null;
  }
}

export function writeCollapsed(
  storageKey: string | undefined,
  collapsed: ReadonlySet<string>,
  store = defaultStore,
): void {
  if (!storageKey) return;
  try {
    store()?.setItem(PREFIX + storageKey, JSON.stringify([...collapsed]));
  } catch {
    // 私密窗口 / 配额满:只是不记住
  }
}

/** 切换一个组的折叠态,返回新集合 */
export function toggleCollapsed(collapsed: ReadonlySet<string>, key: string): Set<string> {
  const next = new Set(collapsed);
  if (next.has(key)) next.delete(key);
  else next.add(key);
  return next;
}