// 装饰模式的经典实现，AOP，在不改变原有函数行为的情况下插入方法
// T: 入参类型，U: 返回结果类型
export class AOP<T, U> {
  funcs: ((...arg: T[]) => U | any)[];
  result: U;
  constructor(
    fn?: (...arg: T[]) => U,
    res?: U,
    initFuncs: ((...arg: T[]) => U | any)[] = [],
  ) {
    this.funcs = initFuncs;
    this.result = res;
    if (fn) {
      this.funcs.push(fn);
    }
  }
  // after:
  after(afterFn?: (...param: T[]) => void) {
    this.funcs.push(afterFn);
    return new AOP<T, U>(null, this.result, this.funcs);
  }
  // before:
  before(before?: (...param: T[]) => void) {
    this.funcs.unshift(before);
    return new AOP<T, U>(null, this.result, this.funcs);
  }
  getFunction() {
    const res = this.result;
    const funcs = this.funcs;
    return function(...params: T[]) {
      funcs.forEach(fn => {
        fn(...params);
      });
      return res;
    };
  }
}