components/omnibox/browser/autocomplete_provider_debouncer.h

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_PROVIDER_DEBOUNCER_H_
#define COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_PROVIDER_DEBOUNCER_H_

#include "base/functional/callback.h"
#include "base/time/time.h"
#include "base/timer/timer.h"

// Debounces a method call, i.e. throttles its call rate by delaying its
// invocations and cancelling pending ones when new ones are requested. Each
// instance should be used in a single thread to avoid bad `callback_`.
class AutocompleteProviderDebouncer {
 public:
  AutocompleteProviderDebouncer(bool from_last_run, int delay_ms);

  ~AutocompleteProviderDebouncer();

  // Request |callback| to be invoked after the debouncing delay. If called
  // while a previous request is still pending, the previous request will be
  // cancelled.
  void RequestRun(base::OnceCallback<void()> callback);

  // Cancels any pending request.
  void CancelRequest();

  // Resets `time_last_run_` to now. Should be called when the debounced method
  // was called externally. E.g., if there are 2 flows to call `X()`:
  // 1) `X()`
  // 2) `debouncer.RequestRun(base::BindOnce(&X))`
  // When (1) occurs prior to (2), it might want to also invoke
  // `debouncer.ResetTimeLastRan()` to make sure the 2nd call to `X()` doesn't
  // occur in rapid succession.
  // Will delay both future `RequestRun()` as well as any pending requests.
  void ResetTimeLastRun();

 private:
  void Run();

  // Whether debounce delays are calculated since |time_last_run_| or the last
  // invocation of |RequestRun|.
  bool from_last_run_ = false;

  // The debounce delay.
  int delay_ms_ = 0;

  // Tracks when to next invoke |callback_|.
  base::OneShotTimer timer_;

  // The last time |Run| was invoked.
  base::TimeTicks time_last_run_;

  // The callback to invoke once |timer_| expires.
  base::OnceCallback<void()> callback_;
};

#endif  // COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_PROVIDER_DEBOUNCER_H_