import { useSyncExternalStore } from 'react'

// 40-line store: state object + action methods that return partial updates.
export function create(def) {
  let state = {}
  const listeners = new Set()
  const api = {}
  for (const [k, v] of Object.entries(def)) {
    if (typeof v === 'function') {
      api[k] = (...args) => {
        const patch = v.apply(state, args)
        if (patch) { state = { ...state, ...patch }; listeners.forEach(l => l()) }
      }
    } else {
      state[k] = v
    }
  }
  api.get = () => state
  api.subscribe = l => { listeners.add(l); return () => listeners.delete(l) }
  api.use = (selector = s => s) => useSyncExternalStore(api.subscribe, () => selector(state), () => selector(state))
  return api
}