/**
 * How far each divider was dragged, kept in this browser: a panel made wider stays wider after a
 * reload, in every project. Best effort, like the folds – a browser that refuses `localStorage`
 * forgets with the page.
 */
import { clamp } from '../ui/math';

const STORAGE_KEY = 'feuerwerk.panel-sizes';

let sizes: Map<string, number> | null = null;

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

function read(): Map<string, number> {
  try {
    const stored: unknown = JSON.parse(storage()?.getItem(STORAGE_KEY) ?? '{}');
    if (typeof stored !== 'object' || stored === null || Array.isArray(stored)) return new Map();
    return new Map(
      Object.entries(stored).filter((entry): entry is [string, number] => Number.isFinite(entry[1])),
    );
  } catch {
    return new Map();
  }
}

/**
 * The size a panel starts with: what was kept under `name`, held to the bounds its divider keeps
 * today, or `fallback` where nothing was kept.
 */
export function panelSize(name: string, fallback: number, min: number, max: number): number {
  sizes ??= read();
  const kept = sizes.get(name);
  return kept === undefined ? fallback : clamp(kept, min, max);
}

export function keepPanelSize(name: string, size: number): void {
  sizes ??= read();
  sizes.set(name, size);
  try {
    storage()?.setItem(STORAGE_KEY, JSON.stringify(Object.fromEntries([...sizes].sort())));
  } catch {
    // Kept for this page only.
  }
}

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