/*
 * @since 2020-11-05 15:24:04
 * @author acrazing <joking.young@gmail.com>
 */

import { identity } from './utils';

/**
 * An `Event` is a dispatchable object, which will notify all the subscribed
 * boxes to mutate these states when it is dispatched. The only way to create
 * an signal is calling the `EventFactory`, which is created by calling `signal()`
 * method.  You don't need to pay attention to any properties of the `Event`.
 *
 * The result of dispatch an `Event` is the data of the `Event`.
 *
 * @stable
 */
export interface Signal<T = any> {
  object: 'signal';
  type: string;
  data: T;
}

/**
 * An `EventFactory` is a function to create an `Event`, which is created by
 * `signal()` method.
 *
 * @stable
 */
export interface SignalFactory<A extends any[], T> {
  type: string;
  (...args: A): Signal<T>;
}

/**
 * Create an `EventFactory` without data.
 *
 * @param type An optional string to identify the type of the created signal.
 *
 * @stable
 */
export function signal(type: string): SignalFactory<[], void>;
/**
 * Create an `EventFactory` which creates an signal, whose value of the data
 * is the first parameter of calling `EventFactory`.
 *
 * @param type An optional string to identify the type of the created signal.
 *
 * @stable
 */
export function signal<T>(type: string): SignalFactory<[T], T>;
/**
 * Create an `EventFactory` which creates an signal, whose value of the data
 * is the return type of `creator`.
 *
 * @param creator a creator will be called with the same parameters when
 *                `EventFactory` is called.
 * @param type An optional string to identify the type of the created signal.
 *
 * @stable
 */
export function signal<A extends any[], T>(
  type: string,
  creator: (...args: A) => T,
): SignalFactory<A, T>;
export function signal(type: string, creator: any = identity): SignalFactory<any[], any> {
  return Object.assign(
    (...args: any[]): Signal<any> => ({ object: 'signal', type, data: creator(...args) }),
    { type },
  );
}