components/sync_driver/revisit/offset_tab_matcher.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_SYNC_DRIVER_OFFSET_TAB_MATCHER_H_
   6 #define COMPONENTS_SYNC_DRIVER_OFFSET_TAB_MATCHER_H_
   7
   8 #include "components/sessions/session_types.h"
   9 #include "components/sync_driver/revisit/page_equality.h"
  10 #include "components/sync_driver/revisit/page_visit_observer.h"
  11
  12 namespace sync_driver {
  13
  14 // This class looks for tabs that have matching pages that are not the current
  15 // navigation entry. This corresponds to the pages you would arrive at if you
  16 // pressed the forward/backwards buttons. The goal is to emit metrics for the
  17 // most recent/current entry. So to break ties of multiple entries that match,
  18 // first the timestamp on the tab is used, followed by the index of the entry.
  19 // This isn't necessarily perfect at determining the most recent, but it should
  20 // be a reasonable enough approximation.
  21 class OffsetTabMatcher {
  22  public:
  23   explicit OffsetTabMatcher(const PageEquality& page_equality);
  24   void Check(const sessions::SessionTab* tab);
  25   void Emit(const PageVisitObserver::TransitionType transition);
  26
  27  private:
  28   int Clamp(int input, int lower, int upper);
  29
  30   const PageEquality page_equality_;
  31   const sessions::SessionTab* best_tab_ = nullptr;
  32   // Invalid while best_tab_ is nullptr.
  33   int best_offset_ = 0;
  34
  35   DISALLOW_COPY_AND_ASSIGN(OffsetTabMatcher);
  36 };
  37
  38 }  // namespace sync_driver
  39
  40 #endif  // COMPONENTS_SYNC_DRIVER_OFFSET_TAB_MATCHER_H_