// Client-side notification store. Surfaces transient toasts AND keeps a history that
// the Notification Center shows (info events, actions awaiting interaction, and app
// errors). History is persisted to localStorage so it survives reloads; action
// callbacks are live-only and dropped on reload.

export type NotifLevel = "info" | "success" | "warning" | "error" | "fatal";

export interface NotifAction {
  label: string;
  onClick: () => void;
}

export interface Notification {
  id: number;
  level: NotifLevel;
  title?: string;
  message: string;
  action?: NotifAction;
  requiresInteraction: boolean;
  ts: number;
  read: boolean;
  dismissed: boolean; // transient toast surface closed (still kept in history)
}

export interface NotifyInput {
  message: string;
  level?: NotifLevel;
  title?: string;
  action?: NotifAction;
  requiresInteraction?: boolean;
}

const HISTORY_KEY = "subfeed.notifications";
const MAX_HISTORY = 100;
const DEFAULT_TTL = 9000;
const ERROR_TTL = 15000;

let items: Notification[] = load();
let listeners: Array<() => void> = [];
let counter = items.reduce((m, n) => Math.max(m, n.id), 0) + 1;

// Cached derived snapshots — useSyncExternalStore needs stable references between
// emits, so we recompute these only when `items` changes.
let cachedActive: Notification[] = [];
let cachedReversed: Notification[] = [];
let cachedUnread = 0;

function load(): Notification[] {
  try {
    const raw = JSON.parse(localStorage.getItem(HISTORY_KEY) || "[]");
    if (!Array.isArray(raw)) return [];
    return raw.map((n) => ({ ...n, action: undefined }) as Notification);
  } catch {
    return [];
  }
}

function persist() {
  try {
    const slim = items.map(({ action: _action, ...n }) => n);
    localStorage.setItem(HISTORY_KEY, JSON.stringify(slim));
  } catch {
    /* ignore quota / serialization errors */
  }
}

function recompute() {
  cachedActive = items.filter((n) => !n.dismissed);
  cachedReversed = [...items].reverse();
  cachedUnread = items.reduce((c, n) => c + (n.read ? 0 : 1), 0);
}

function emit() {
  items = items.slice(-MAX_HISTORY);
  recompute();
  persist();
  listeners.forEach((l) => l());
}

recompute();

export function subscribe(listener: () => void): () => void {
  listeners.push(listener);
  return () => {
    listeners = listeners.filter((l) => l !== listener);
  };
}

export function notify(input: NotifyInput): number {
  const id = counter++;
  const requiresInteraction = input.requiresInteraction ?? false;
  const level = input.level ?? "info";
  items = [
    ...items,
    {
      id,
      level,
      title: input.title,
      message: input.message,
      action: input.action,
      requiresInteraction,
      ts: Date.now(),
      read: false,
      dismissed: false,
    },
  ];
  emit();
  if (!requiresInteraction) {
    const ttl = level === "error" || level === "fatal" ? ERROR_TTL : DEFAULT_TTL;
    setTimeout(() => dismiss(id), ttl);
  }
  return id;
}

/** Back-compat: a simple info toast with an optional inline action (e.g. Undo). */
export function toast(message: string, action?: NotifAction): number {
  return notify({ message, action });
}

/** Close the transient toast surface; the entry stays in the center's history. */
export function dismiss(id: number): void {
  items = items.map((n) => (n.id === id ? { ...n, dismissed: true } : n));
  emit();
}

export function markAllRead(): void {
  if (items.every((n) => n.read)) return;
  items = items.map((n) => (n.read ? n : { ...n, read: true }));
  emit();
}

export function clearAll(): void {
  if (items.length === 0) return;
  items = [];
  emit();
}

export const getActiveToasts = (): Notification[] => cachedActive;
export const getNotifications = (): Notification[] => cachedReversed;
export const getUnreadCount = (): number => cachedUnread;