import { Subscriber, Observable, Operator, TeardownLogic } from 'rxjs';

class FinalizeWithLastSubscriber<T> extends Subscriber<T> {
  /**
   * @param destination
   * @param callback
   * @param value default value
   */
  constructor(destination: Subscriber<T>, private readonly callback: (value: T) => void, private value: T) {
    super(destination);
  }

  _next(value: T) {
    this.value = value;
    this.destination.next?.(value);
  }

  _complete() {
    try {
      const { callback } = this;
      callback(this.value);
    } catch (error) {
      this.destination.error?.(error);
    }
    this.destination.complete?.();
  }
}

class FinalizeWithLastOperator<T> implements Operator<T, T> {
  constructor(private readonly callback: (value: T) => void, private readonly defaultValue: T) {}

  call(subscriber: Subscriber<T>, source: Observable<T>): TeardownLogic {
    return source.subscribe(new FinalizeWithLastSubscriber(subscriber, this.callback, this.defaultValue));
  }
}

export function finalizeWithLast<T>(callback: (value: T) => void, defaultValue: T) {
  return function finalizeWithLastOperatorFunction(source: Observable<T>): Observable<T> {
    return source.lift(new FinalizeWithLastOperator(callback, defaultValue));
  };
}