export type AllKeys<T> = T extends any ? keyof T : never

type Primitive = boolean | number | string

export type ReadonlyIfObject<Value> = Value extends undefined
  ? Value
  : Value extends (...args: any) => any
  ? Value
  : Value extends Primitive
  ? Value
  : Value extends object
  ? Readonly<Value>
  : Value

/**
 * Store object.
 */
export interface ReadableAtom<Value = any> {
  /**
   * Get store value.
   *
   * In contrast with {@link ReadableAtom#value} this value will be always
   * initialized even if store had no listeners.
   *
   * ```js
   * $store.get()
   * ```
   *
   * @returns Store value.
   */
  get(): Value

  /**
   * Low-level attribute to read store’s initial value.
   */
  readonly init: undefined | Value

  /**
   * Listeners count.
   */
  readonly lc: number

  /**
   * Subscribe to store changes.
   *
   * In contrast with {@link Store#subscribe} it do not call listener
   * immediately.
   *
   * @param listener Callback with store value and old value.
   * @returns Function to remove listener.
   */
  listen(
    listener: (
      value: ReadonlyIfObject<Value>,
      oldValue: ReadonlyIfObject<Value>
    ) => void
  ): () => void

  /**
   * Low-level method to notify listeners about changes in the store.
   *
   * Can cause unexpected behaviour when combined with frontend frameworks
   * that perform equality checks for values, such as React.
   */
  notify(oldValue?: ReadonlyIfObject<Value>): void

  /**
   * Unbind all listeners.
   */
  off(): void

  /**
   * Subscribe to store changes and call listener immediately.
   *
   * ```
   * import { $router } from '../store'
   *
   * $router.subscribe(page => {
   *   console.log(page)
   * })
   * ```
   *
   * @param listener Callback with store value and old value.
   * @returns Function to remove listener.
   */
  subscribe(
    listener: (
      value: ReadonlyIfObject<Value>,
      oldValue?: ReadonlyIfObject<Value>
    ) => void
  ): () => void

  /**
   * Low-level method to read store’s value without calling `onStart`.
   *
   * Try to use only {@link ReadableAtom#get}.
   * Without subscribers, value can be undefined.
   */
  readonly value: undefined | Value
}

/**
 * Store with a way to manually change the value.
 */
export interface WritableAtom<Value = any> extends ReadableAtom<Value> {
  /**
   * Change store value.
   *
   * ```js
   * $router.set({ path: location.pathname, page: parse(location.pathname) })
   * ```
   *
   * @param newValue New store value.
   */
  set(newValue: Value): void
}

export interface PreinitializedWritableAtom<Value> extends WritableAtom<Value> {
  readonly value: Value
}

export type Atom<Value = any> = ReadableAtom<Value> | WritableAtom<Value>

export declare let notifyId: number
/**
 * Create store with atomic value. It could be a string or an object, which you
 * will replace completely.
 *
 * If you want to change keys in the object inside store, use {@link map}.
 *
 * ```js
 * import { atom, onMount } from 'nanostores'
 *
 * // Initial value
 * export const $router = atom({ path: '', page: 'home' })
 *
 * function parse () {
 *   $router.set({ path: location.pathname, page: parse(location.pathname) })
 * }
 *
 * // Listen for URL changes on first store’s listener.
 * onMount($router, () => {
 *   parse()
 *   window.addEventListener('popstate', parse)
 *   return () => {
 *     window.removeEventListener('popstate', parse)
 *   }
 * })
 * ```
 *
 * @param initialValue Initial value of the store.
 * @returns The store object with methods to subscribe.
 */
export function atom<Value, StoreExt = object>(
  ...args: undefined extends Value ? [] | [Value] : [Value]
): PreinitializedWritableAtom<Value> & StoreExt

/**
 * Change store type for readonly for export.
 *
 * ```ts
 * import { readonlyType } from 'nanostores'
 *
 * const $storePrivate = atom(0)
 *
 * export const $store = readonlyType($storePrivate)
 * ```
 *
 * @param store The store to be exported.
 * @returns The readonly store.
 */
export function readonlyType<Value>(
  store: ReadableAtom<Value>
): ReadableAtom<Value>