import Function from "./Function";

export default class InfiniteIterator<E> implements IterableIterator<E> {
  private current: E;
  private nextElement: E;

  constructor(private initial: E, private func: Function<E, E>) {
    this.current = null;
    this.nextElement = initial;
  }

  public static of<E>(initial: E, func: Function<E, E>): InfiniteIterator<E> {
    return new InfiniteIterator<E>(initial, func);
  }

  public [Symbol.iterator](): IterableIterator<E> {
    return this;
  }

  public reset(): void {
    this.current = null;
    this.nextElement = this.initial;
  }

  public hasNext(): boolean {
    try{
      if(this.nextElement == null){
        this.nextElement = this.func(this.current);
      }
      return this.nextElement != null;
    }
    catch(e){
      return false;
    }
  }

  public next(): IteratorResult<E> {
    if(this.nextElement == null){
      throw new Error("No more elements");
    }
    
    this.current = this.nextElement;
    this.nextElement = null;
    return { value: this.current, done: this.hasNext() };
  }
}