Extending the UserClassifier to actually support classification.

components/ntp_snippets/user_classifier.h

Index: components/ntp_snippets/user_classifier.h
diff --git a/components/ntp_snippets/user_classifier.h b/components/ntp_snippets/user_classifier.h
index 3314884606f42b125937584ed468d285b0c3ad1d..b0ebc39420c4d8c884743f9eb18fad5f8dfdb915 100644
--- a/components/ntp_snippets/user_classifier.h
+++ b/components/ntp_snippets/user_classifier.h
@@ -5,7 +5,10 @@
 #ifndef COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_
 #define COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_
 
+#include <string>
+
 #include "base/macros.h"
+#include "base/time/time.h"
 
 class PrefRegistrySimple;
 class PrefService;
@@ -14,10 +17,16 @@ namespace ntp_snippets {
 
 // Collects data about user usage patterns of content suggestions, computes
 // long-term user metrics locally using pref, and reports the metrics to UMA.
-// TODO(jkrcal): Add classification of users based on the metrics and getters
-// for the classification as well as for the metrics.
+// Based on these lon-term user metrics, it classifies the user in a UserClass.
 class UserClassifier {
  public:
+  // Enumeration listing user classes
+  enum class UserClass {
+    OCCASIONAL_NTP_USER,
+    NORMAL_NTP_USER,
+    FREQUENT_NTP_USER,
+  };
+
   // The provided |pref_service| may be nullptr in unit-tests.
   explicit UserClassifier(PrefService* pref_service);
   ~UserClassifier();
@@ -36,22 +45,35 @@ class UserClassifier {
   // When the user clicks on some suggestions or on some "More" button.
   void OnSuggestionsUsed();
 
- private:
-  // The event has happened, recompute and store the metric accordingly.
-  void UpdateMetricOnEvent(const char* metric_pref_name,
-                           const char* last_time_pref_name);
+  // Get the estimate frequencies of events that the classifier tracks.

[Marc Treib, 2016/09/19 15:20:16]

nit: these return intervals, not frequencies.

All of these should probably be const?

[jkrcal, 2016/09/19 18:45:25]

Done.

+  double GetEstimatedAvgTimeToOpenNTP();
+  double GetEstimatedAvgTimeToShowSuggestions();
+  double GetEstimatedAvgTimeToUseSuggestions();
 
-  // Compute the number of hours between two events for the given metric value
-  // assuming the events were equally distributed.
-  double GetEstimateHoursBetweenEvents(const char* metric_pref_name);
+  // Return the classification of the current user.
+  UserClass GetUserClass();
+  std::string GetUserClassDescription();

[Marc Treib, 2016/09/19 15:20:16]

Mark this "ForDebugging" or something like that? Otherwise people might expect
the string to be translated etc.

[jkrcal, 2016/09/19 18:45:25]

Done.

 
-  // Returns the number of hours since the last event of the same type or
-  // DBL_MAX if there is no last event of that type.
+  // Resets the classification (emulates a fresh upgrade / install).
+  void ClearClassificationForTesting();

[Marc Treib, 2016/09/19 15:20:16]

s/ForTesting/ForDebugging/

"ForTesting" implies it's only used in (unit) tests.

[jkrcal, 2016/09/19 18:45:25]

Done.

+
+ private:
+  // The event has happened, recompute the metric accordingly. Then store and
+  // return the new value.
+  double UpdateMetricOnEvent(const char* metric_pref_name,
+                           const char* last_time_pref_name);

[Marc Treib, 2016/09/19 15:20:16]

misaligned

[jkrcal, 2016/09/19 18:45:25]

Done.

+  // No event has happened but we need to get up-to-date metric, recompute and
+  // return the new value. This function does not store the recomputed metric.
+  double GetUpToDateMetricValue(const char* metric_pref_name,
+                                const char* last_time_pref_name);
+
+  // Returns the number of hours since the last event of the same type.
+  // If there is no last event of that type, assume it happened just now (call
+  // SetLastTimeToNow()), and return 0.
   double GetHoursSinceLastTime(const char* last_time_pref_name);
   void SetLastTimeToNow(const char* last_time_pref_name);
 
   PrefService* pref_service_;
-  double const discount_rate_per_hour_;
 
   DISALLOW_COPY_AND_ASSIGN(UserClassifier);
 };