/**
 * 单例化一个class
 * 使用方法:
 * @singleton
 * class Test {}
 * new Test() === new Test() // returns `true`
 * 也可以不使用 decorator
 * const TestSingleton = singleton(Test)
 * new TestSingleton() === new TestSingleton() //returns 'true'
 */

export const SINGLETON_KEY = Symbol()

export type Singleton<T extends new (...args: any[]) => any> = T & {
  [SINGLETON_KEY]: T extends new (...args: any[]) => infer I ? I : never
}
export const singleton = <T extends new (...args: any[]) => any>(classTarget: T) =>
  new Proxy(classTarget, {
    construct(target: Singleton<T>, argumentsList, newTarget) {
      // Skip proxy for children
      if (target.prototype !== newTarget.prototype) {
        return Reflect.construct(target, argumentsList, newTarget)
      }
      if (!target[SINGLETON_KEY]) {
        target[SINGLETON_KEY] = Reflect.construct(target, argumentsList, newTarget)
      }
      return target[SINGLETON_KEY]
    },
  })