/**
 * Which groups of rows are folded (#290), kept in this browser: a group folded once stays folded
 * for every selection that shows it, and after a reload. Best effort, like the saves – a browser
 * that refuses `localStorage` forgets with the page.
 */
import { Theme } from '../ui/Theme';

const STORAGE_KEY = 'game-maker.folded-sections';

let folded: Set<string> | null = null;

function storage(): Pick<Storage, 'getItem' | 'setItem'> | null {
  try {
    return typeof window === 'undefined' ? null : window.localStorage;
  } catch {
    return null;
  }
}

function read(): Set<string> {
  try {
    const stored: unknown = JSON.parse(storage()?.getItem(STORAGE_KEY) ?? '[]');
    return new Set(Array.isArray(stored) ? stored.filter((key) => typeof key === 'string') : []);
  } catch {
    return new Set();
  }
}

/**
 * Names a group: the panel it stands in and its title, numbers left out – "3 OBJECTS SELECTED" and
 * "KEY AT FRAME 12" are the same group whatever they count.
 */
export function foldKey(scope: string, title: string): string {
  return `${scope}:${title.replace(/\d+/g, '#')}`;
}

export function isFolded(key: string): boolean {
  folded ??= read();
  return folded.has(key);
}

export function setFolded(key: string, on: boolean): void {
  folded ??= read();
  if (on) folded.add(key);
  else folded.delete(key);
  try {
    storage()?.setItem(STORAGE_KEY, JSON.stringify([...folded].sort()));
  } catch {
    // Kept for this page only.
  }
}

/**
 * What a list with a header of its own takes to fold like the groups of the column it stands in:
 * the band reaches across the column's padding, and the fold is remembered under the list's title.
 */
export function listFold(
  scope: string,
  title: string,
): { bleed: number; collapsed: boolean; onFold: (collapsed: boolean) => void } {
  const key = foldKey(scope, title.toUpperCase());
  return { bleed: Theme.padding, collapsed: isFolded(key), onFold: (on) => setFolded(key, on) };
}

/** Forgets what was read, so the next question asks the browser again (tests). */
export function resetFolds(): void {
  folded = null;
}