import { useSyncExternalStore } from 'react';

// Local-only friend nickname overrides. Stored in localStorage keyed by the
// peer's user-id. Empty/missing value = use the real display name.
// Local-only by design — friends never see your nickname for them.

const STORAGE_KEY = 'chatapp.friendNicknames.v1';

let cache: Record<string, string> | null = null;
const listeners = new Set<() => void>();

function load(): Record<string, string> {
  if (cache) return cache;
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) { cache = {}; return cache; }
    const parsed = JSON.parse(raw) as unknown;
    if (parsed && typeof parsed === 'object') {
      cache = {};
      for (const [k, v] of Object.entries(parsed as Record<string, unknown>)) {
        if (typeof v === 'string' && v.trim().length > 0) cache[k] = v;
      }
      return cache;
    }
  } catch { /* corrupted; fall through */ }
  cache = {};
  return cache;
}

function persist(): void {
  try { window.localStorage.setItem(STORAGE_KEY, JSON.stringify(cache ?? {})); }
  catch { /* quota / private mode */ }
  for (const l of listeners) l();
}

export function getNickname(userId: string): string | null {
  return load()[userId] ?? null;
}

export function setNickname(userId: string, nickname: string | null): void {
  const store = load();
  const trimmed = nickname?.trim() ?? '';
  if (trimmed.length === 0) {
    if (!(userId in store)) return;
    delete store[userId];
  } else {
    if (store[userId] === trimmed) return;
    store[userId] = trimmed;
  }
  persist();
}

// Reactive hook: returns the current nickname for a user, or `fallback`
// when no nickname is set. Re-renders when ANY nickname changes (cheap,
// the set is small).
export function useNickname(userId: string | null | undefined, fallback: string): string {
  const subscribe = (cb: () => void) => {
    listeners.add(cb);
    return () => { listeners.delete(cb); };
  };
  const getSnapshot = () => (userId ? getNickname(userId) : null);
  const nickname = useSyncExternalStore(subscribe, getSnapshot, getSnapshot);
  return nickname ?? fallback;
}