/**
 * static/js/state.js
 * Centralised reactive state store.
 * Components subscribe to state slices and are notified on change.
 */

const _state = {
  instructions: [],   // InstructionItem[]
  status: null,       // StatusResponse | null
  config: null,       // ConfigResponse | null
  serverOnline: false,
};

const _listeners = {};  // key -> Set<fn>

export const state = {
  get(key) {
    return _state[key];
  },

  set(key, value) {
    _state[key] = value;
    (_listeners[key] || new Set()).forEach(fn => fn(value));
  },

  subscribe(key, fn) {
    if (!_listeners[key]) _listeners[key] = new Set();
    _listeners[key].add(fn);
    // Immediately call with current value
    fn(_state[key]);
    return () => _listeners[key].delete(fn);   // unsubscribe
  },
};