//#region src/observer/index.d.ts
/**
* Observer utilities
*
* @example
* ```ts
* import { observe } from '@kazupon/jts-utils/observer'
* ```
*
* @module observer
*/
/**
* @license MIT
* @author kazuya kawaguchi (a.k.a. kazupon)
*/
/**
* State value subscribe handler
*/
type ObservableStateSubscribeHandler<State> = (state: State) => void;
/**
* State value unsubscribe handler
*/
interface ObservableStateUnsubscribeHandler extends Disposable {
  (): void;
}
/**
* State value observable
*/
interface Observable<State> extends Disposable {
  /**
  * listener count
  */
  readonly listenerCount: number;
  /**
  * add state subscription
  *
  * @param listener - listener
  * @returns unsubscribe handler
  */
  subscribe(listener: ObservableStateSubscribeHandler<State>): ObservableStateUnsubscribeHandler;
  /**
  * notify state value
  *
  * @param state - updated state value
  */
  notify(state: State): void;
  /**
  * dispose observable
  */
  dispose(): void;
}
/**
* observe state value
*
* @example
* ```ts
* import { observe } from '@kazupon/jts-utils'
*
* // create observable
* const observer = observe<{ a: number }>()
*
* // subscribe state change
* const unsubscribe = observer.subscribe((state) => {
*   console.log(state)
* })
*
* // notify state change
* observer.notify({ a: 1 })
*
* // unsubscribe
* unsubscribe()
* ```
*
* if javascript runtime supports `Symbol.dispose`, you can use it as follows:
*
* @example
* ```ts
* import { observe } from '@kazupon/jts-utils'
*
* // create observable with `using` syntax
* // when the scope is exited, `observer.dispose` will be called automatically
* using observer = observe<{ a: number }>()
*
* const unsubscribe1 = observer.subscribe((state) => {
*  console.log(state)
* })
*
* // subscribe with `using` syntax
* // when the scope is exited, `unsubscribe2` will be called automatically
* using unsubscribe2 = observer.subscribe((state) => {
*  console.log(state)
* })
*
* observer.notify({ a: 1 })
* ```
*
* @returns observable state value
*/
declare function observe<State>(): Readonly<Observable<State>>;
//#endregion
export { Observable, ObservableStateSubscribeHandler, ObservableStateUnsubscribeHandler, observe };