export class Lock<T> {
  private _isAcquired = false;
  private _acquiredMap: Map<T, boolean> = new Map<T, boolean>();
  private waitingMap: Map<T, (() =>  void)[]> = new Map<T, (() =>  void)[]>();
  private waitingList: (() => void)[]  = [];

  acquire(key?: T): Promise<void> {
    if (key) {
      if (!this._acquiredMap.has(key) || !this._acquiredMap.get(key)) {
        this._acquiredMap.set(key, true);
        return Promise.resolve();
      }
    }
    else if (!this._isAcquired) {
      this._isAcquired = true;
      return Promise.resolve();
    }

    return new Promise((resolve, reject) => {
      if (key) {
        if (this.waitingMap.has(key)) {
          let resolvers = this.waitingMap.get(key);
          resolvers.push(resolve);
          this.waitingMap.set(key, resolvers);
        }
        else {
          this.waitingMap.set(key, [resolve]);
        }
      }
      else {
        this.waitingList.push(resolve);
      }
    })
  }

  isAcquired(key?: T): boolean {
    if (key) {
      if (!this._acquiredMap.has(key)) {
        return false;
      }
      else {
        return this._acquiredMap.get(key);
      }
    }
    else {
      return this._isAcquired;
    }
  }

  release(key?: T): void {
    if (key) {
      if (!this._acquiredMap.has(key) || !this._acquiredMap.get(key)) {
        throw new Error(
          "Please acquire a lock for " + key + " before releasing!!"
        );
      }
      else {
        if (this.waitingMap.get(key)?.length > 0) {
          let resolve = this.waitingMap.get(key).shift();
          resolve();
        }
        else {
          if (this.waitingMap.has(key)) {
            this.waitingMap.delete(key);
          }

          this._acquiredMap.set(key, false);
        }
      }
    }
    else {
      if (!this._isAcquired) {
        throw new Error("Please acquire a lock before releasing!!");
      }
      else {
        if (this.waitingList.length > 0) {
          let resolve = this.waitingList.shift();
          resolve();
        }
        else {
          this._isAcquired = false;
        }
      }
    }
  }
}