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+import { Subscription } from '../Subscription';
+
+import { MonoTypeOperatorFunction, ObservableInput } from '../types';
+import { operate } from '../util/lift';
+import { createOperatorSubscriber } from './OperatorSubscriber';
+import { innerFrom } from '../observable/innerFrom';
+
+/**
+ * An object interface used by {@link throttle} or {@link throttleTime} that ensure
+ * configuration options of these operators.
+ *
+ * @see {@link throttle}
+ * @see {@link throttleTime}
+ */
+export interface ThrottleConfig {
+  /**
+   * If `true`, the resulting Observable will emit the first value from the source
+   * Observable at the **start** of the "throttling" process (when starting an
+   * internal timer that prevents other emissions from the source to pass through).
+   * If `false`, it will not emit the first value from the source Observable at the
+   * start of the "throttling" process.
+   *
+   * If not provided, defaults to: `true`.
+   */
+  leading?: boolean;
+  /**
+   * If `true`, the resulting Observable will emit the last value from the source
+   * Observable at the **end** of the "throttling" process (when ending an internal
+   * timer that prevents other emissions from the source to pass through).
+   * If `false`, it will not emit the last value from the source Observable at the
+   * end of the "throttling" process.
+   *
+   * If not provided, defaults to: `false`.
+   */
+  trailing?: boolean;
+}
+
+/**
+ * Emits a value from the source Observable, then ignores subsequent source
+ * values for a duration determined by another Observable, then repeats this
+ * process.
+ *
+ * <span class="informal">It's like {@link throttleTime}, but the silencing
+ * duration is determined by a second Observable.</span>
+ *
+ * ![](throttle.svg)
+ *
+ * `throttle` emits the source Observable values on the output Observable
+ * when its internal timer is disabled, and ignores source values when the timer
+ * is enabled. Initially, the timer is disabled. As soon as the first source
+ * value arrives, it is forwarded to the output Observable, and then the timer
+ * is enabled by calling the `durationSelector` function with the source value,
+ * which returns the "duration" Observable. When the duration Observable emits a
+ * value, the timer is disabled, and this process repeats for the
+ * next source value.
+ *
+ * ## Example
+ *
+ * Emit clicks at a rate of at most one click per second
+ *
+ * ```ts
+ * import { fromEvent, throttle, interval } from 'rxjs';
+ *
+ * const clicks = fromEvent(document, 'click');
+ * const result = clicks.pipe(throttle(() => interval(1000)));
+ *
+ * result.subscribe(x => console.log(x));
+ * ```
+ *
+ * @see {@link audit}
+ * @see {@link debounce}
+ * @see {@link delayWhen}
+ * @see {@link sample}
+ * @see {@link throttleTime}
+ *
+ * @param durationSelector A function that receives a value from the source
+ * Observable, for computing the silencing duration for each source value,
+ * returned as an `ObservableInput`.
+ * @param config A configuration object to define `leading` and `trailing`
+ * behavior. Defaults to `{ leading: true, trailing: false }`.
+ * @return A function that returns an Observable that performs the throttle
+ * operation to limit the rate of emissions from the source.
+ */
+export function throttle<T>(durationSelector: (value: T) => ObservableInput<any>, config?: ThrottleConfig): MonoTypeOperatorFunction<T> {
+  return operate((source, subscriber) => {
+    const { leading = true, trailing = false } = config ?? {};
+    let hasValue = false;
+    let sendValue: T | null = null;
+    let throttled: Subscription | null = null;
+    let isComplete = false;
+
+    const endThrottling = () => {
+      throttled?.unsubscribe();
+      throttled = null;
+      if (trailing) {
+        send();
+        isComplete && subscriber.complete();
+      }
+    };
+
+    const cleanupThrottling = () => {
+      throttled = null;
+      isComplete && subscriber.complete();
+    };
+
+    const startThrottle = (value: T) =>
+      (throttled = innerFrom(durationSelector(value)).subscribe(createOperatorSubscriber(subscriber, endThrottling, cleanupThrottling)));
+
+    const send = () => {
+      if (hasValue) {
+        // Ensure we clear out our value and hasValue flag
+        // before we emit, otherwise reentrant code can cause
+        // issues here.
+        hasValue = false;
+        const value = sendValue!;
+        sendValue = null;
+        // Emit the value.
+        subscriber.next(value);
+        !isComplete && startThrottle(value);
+      }
+    };
+
+    source.subscribe(
+      createOperatorSubscriber(
+        subscriber,
+        // Regarding the presence of throttled.closed in the following
+        // conditions, if a synchronous duration selector is specified - weird,
+        // but legal - an already-closed subscription will be assigned to
+        // throttled, so the subscription's closed property needs to be checked,
+        // too.
+        (value) => {
+          hasValue = true;
+          sendValue = value;
+          !(throttled && !throttled.closed) && (leading ? send() : startThrottle(value));
+        },
+        () => {
+          isComplete = true;
+          !(trailing && hasValue && throttled && !throttled.closed) && subscriber.complete();
+        }
+      )
+    );
+  });
+}