[TTS] Add aggregation of CTR metrics to the CS component.

components/contextual_search/browser/ctr_aggregator.h

Index: components/contextual_search/browser/ctr_aggregator.h
diff --git a/components/contextual_search/browser/ctr_aggregator.h b/components/contextual_search/browser/ctr_aggregator.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Provides aggregation of feature usage by tracking impressions and clicks
+// over 1-week and 28-day intervals.  Impressions are views of some UX and
+// clicks are any measured interaction with that UX, yielding CTR -- Click
+// Through Rate.
+// Used by Contextual Search to record impressions of the Bar and CTR of
+// panel opens to use as signals for Tap triggering.
+
+#ifndef COMPONENTS_CONTEXTUAL_SEARCH_BROWSER_CTR_AGGREGATOR_H_
+#define COMPONENTS_CONTEXTUAL_SEARCH_BROWSER_CTR_AGGREGATOR_H_
+
+#include <string>
+
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "components/contextual_search/browser/weekly_activity_storage.h"
+
+namespace contextual_search {
+
+// Number of weeks of data needed for 28 days.
+const int kNumWeeksNeededFor28DayData = 4;
+
+// Usage: Create a CTRAggregator and start recording impressions or reading
+// aggregated data.  Get data from the previous week or previous 4-week period
+// that ended with the previous week.
+// A new week starts at an arbitrary time based on seconds since the Epoch.
+// The data from the previous week and previous 28-day period are guaranteed to
+// be complete only if the HasPrevious method returns true.  If one of the data
+// accessors is called when the data is not complete invalid data may be
+// returned.
+class CTRAggregator {
+ public:
+  // Constructs a CTRAggregator using the given |storage| mechanism.
+  // Data is stored by |storage| typically on persistent device-local storage.
+  // A callback through the storage interface may occur at construction time,
+  // so the |storage| must be fully initialized when this constructor is
+  // called.
+  CTRAggregator(WeeklyActivityStorage& storage);
+  ~CTRAggregator();
+
+  // Records an impression.  Records a click if |did_click| is true.
+  void RecordImpression(bool did_click);
+
+  // Returns whether we have the previous week's data for this user.
+  bool HasPreviousWeekData();
+
+  // Gets the number of impressions from the previous week.
+  // Callers must check if there is previous week's data for this user, or
+  // invalid data may be returned.
+  int GetPreviousWeekImpressions();
+
+  // Gets the CTR from the previous week.
+  // Callers must check if there is previous week's data for this user, or
+  // invalid data may be returned.
+  float GetPreviousWeekCTR();
+
+  // Returns whether we have data from a 28 day period ending in the previous
+  // week.
+  bool HasPrevious28DayData();
+
+  // Gets the number of impressions from a 28 day period ending in the previous
+  // week.
+  // Callers must check if there is previous 28 day data for this user, or
+  // invalid data may be returned.
+  int GetPrevious28DayImpressions();
+
+  // Gets the CTR from a 28 day period ending in the previous week.
+  // Callers must check if there is previous 28 day data for this user, or
+  // invalid data may be returned.
+  float GetPrevious28DayCTR();
+
+ private:
+  // This implementation uses a fixed number of bins to store integer impression
+  // and click data for the most recent N weeks, where N = 5 (in order to keep 4
+  // complete weeks).  Another bin keeps track of the current week being
+  // written.  Yet another bin records when data was first stored or accessed so
+  // we can know when a time period has complete data.
+  friend class CTRAggregatorTest;
+  FRIEND_TEST_ALL_PREFIXES(CTRAggregatorTest, SimpleOperationTest);
+  FRIEND_TEST_ALL_PREFIXES(CTRAggregatorTest, MultiWeekTest);
+  FRIEND_TEST_ALL_PREFIXES(CTRAggregatorTest, SkipOneWeekTest);
+  FRIEND_TEST_ALL_PREFIXES(CTRAggregatorTest, SkipThreeWeeksTest);
+  FRIEND_TEST_ALL_PREFIXES(CTRAggregatorTest, SkipFourWeeksTest);
+
+  // Constructs an instance for testing; sets the week.
+  CTRAggregator(WeeklyActivityStorage& storage, int week_number);
+  // For testing, increments the current week number by |weeks|.
+  void IncrementWeek(int weeks);
+
+  // Gets the number of clicks from the previous week.
+  // Callers must check if there is previous week's data for this user, or
+  // invalid data may be returned.
+  int GetPreviousWeekClicks();
+  // Gets the number of clicks from a 28 day period ending in the previous
+  // week.
+  // Callers must check if there is previous 28 day data for this user, or
+  // invalid data may be returned.
+  int GetPrevious28DayClicks();
+
+  // Stores the weekly activity data.
+  WeeklyActivityStorage& storage_;
+
+  // The current week number, expressed as the number of weeks since Epoch.
+  int week_number_;
+
+  DISALLOW_COPY_AND_ASSIGN(CTRAggregator);
+};
+
+}  // namespace contextual_search
+
+#endif  // COMPONENTS_CONTEXTUAL_SEARCH_BROWSER_CTR_AGGREGATOR_H_