export default class FiniteStateMachine<S extends string | number> {
  private currentState: S | null = null;
  /** 状态 -> 处于该状态的总时长 */
  private stateToTime = new Map<S, number>();
  /** 前一次结算总时长的时间戳 */
  private lastTimeStamp = 0;

  /** 初始化状态 */
  init(states: S[], initState?: S) {
    states.forEach((state) => {
      this.stateToTime.set(state, 0);
    });
    if (initState !== undefined) {
      this.lastTimeStamp = Date.now();
      this.currentState = initState;
    }
  }

  getCurrent() {
    return this.currentState;
  }

  /** 切换状态 */
  switchTo(state: S) {
    if (!this.stateToTime.has(state)) {
      console.error(`the state: ${state} has not been registered!`);
      return;
    }
    if (this.currentState === state) {
      return;
    }
    const time = Date.now();
    const period = time - this.lastTimeStamp;
    if (this.currentState !== null) {
      const passTime = this.stateToTime.get(this.currentState) || 0;
      this.stateToTime.set(this.currentState, period + passTime);
    }
    this.currentState = state;
    this.lastTimeStamp = time;
  }

  /** 立刻结算某个状态的时长 */
  updateTime(state: S) {
    if (!this.stateToTime.has(state)) {
      console.error(`the state: ${state} has not been registered!`);
      return;
    }
    if (this.currentState !== state) {
      return;
    }
    const time = Date.now();
    const period = time - this.lastTimeStamp;
    const passTime = this.stateToTime.get(this.currentState) || 0;
    this.stateToTime.set(this.currentState, period + passTime);
    this.lastTimeStamp = time;
  }

  /** 将某个状态的时长清零 */
  resetTime(state: S) {
    if (!this.stateToTime.has(state)) {
      console.error(`the state: ${state} has not been registered!`);
      return;
    }
    this.stateToTime.set(state, 0);
  }

  /** 获取处于某状态的总时长
   * @param immediate 是否立即结算
   */
  getTime(state: S, immediate = false) {
    if (immediate) this.updateTime(state);
    return this.stateToTime.get(state) ?? 0;
  }
}