import { async } from '../scheduler/async';
import { Operator } from '../Operator';
import { Scheduler } from '../Scheduler';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { Subscription, TeardownLogic } from '../Subscription';

/**
 * Ignores source values for `duration` milliseconds, then emits the most recent
 * value from the source Observable, then repeats this process.
 *
 * <span class="informal">When it sees a source values, it ignores that plus
 * the next ones for `duration` milliseconds, and then it emits the most recent
 * value from the source.</span>
 *
 * <img src="./img/auditTime.png" width="100%">
 *
 * `auditTime` is similar to `throttleTime`, but emits the last value from the
 * silenced time window, instead of the first value. `auditTime` emits the most
 * recent value from the source Observable on the output Observable as soon as
 * its internal timer becomes disabled, and ignores source values while the
 * timer is enabled. Initially, the timer is disabled. As soon as the first
 * source value arrives, the timer is enabled. After `duration` milliseconds (or
 * the time unit determined internally by the optional `scheduler`) has passed,
 * the timer is disabled, then the most recent source value is emitted on the
 * output Observable, and this process repeats for the next source value.
 * Optionally takes a {@link Scheduler} for managing timers.
 *
 * @example <caption>Emit clicks at a rate of at most one click per second</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.auditTime(1000);
 * result.subscribe(x => console.log(x));
 *
 * @see {@link audit}
 * @see {@link debounceTime}
 * @see {@link delay}
 * @see {@link sampleTime}
 * @see {@link throttleTime}
 *
 * @param {number} duration Time to wait before emitting the most recent source
 * value, measured in milliseconds or the time unit determined internally
 * by the optional `scheduler`.
 * @param {Scheduler} [scheduler=async] The {@link Scheduler} to use for
 * managing the timers that handle the rate-limiting behavior.
 * @return {Observable<T>} An Observable that performs rate-limiting of
 * emissions from the source Observable.
 * @method auditTime
 * @owner Observable
 */
export function auditTime<T>(this: Observable<T>, duration: number, scheduler: Scheduler = async): Observable<T> {
  return this.lift(new AuditTimeOperator(duration, scheduler));
}

class AuditTimeOperator<T> implements Operator<T, T> {
  constructor(private duration: number,
              private scheduler: Scheduler) {
  }

  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
    return source.subscribe(new AuditTimeSubscriber(subscriber, this.duration, this.scheduler));
  }
}

/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class AuditTimeSubscriber<T> extends Subscriber<T> {

  private value: T;
  private hasValue: boolean = false;
  private throttled: Subscription;

  constructor(destination: Subscriber<T>,
              private duration: number,
              private scheduler: Scheduler) {
    super(destination);
  }

  protected _next(value: T): void {
    this.value = value;
    this.hasValue = true;
    if (!this.throttled) {
      this.add(this.throttled = this.scheduler.schedule(dispatchNext, this.duration, this));
    }
  }

  clearThrottle(): void {
    const { value, hasValue, throttled } = this;
    if (throttled) {
      this.remove(throttled);
      this.throttled = null;
      throttled.unsubscribe();
    }
    if (hasValue) {
      this.value = null;
      this.hasValue = false;
      this.destination.next(value);
    }
  }
}

function dispatchNext<T>(subscriber: AuditTimeSubscriber<T>): void {
  subscriber.clearThrottle();
}