📰 Tweak the suggestion ranks for UMA to handle fetchMore

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java
index c4ecfd880faeb8c229a9edc9d5489d7c293eb21d..bc2c4b0e4685f59dc7a0e97a182bafbee7255ca3 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SectionList.java
@@ -32,8 +32,10 @@
     private final Map<Integer, SuggestionsSection> mSections = new LinkedHashMap<>();
     private final NewTabPageManager mNewTabPageManager;
     private final OfflinePageBridge mOfflinePageBridge;
+    private final SuggestionRanker mSuggestionRanker;
 
     public SectionList(NewTabPageManager newTabPageManager, OfflinePageBridge offlinePageBridge) {
+        mSuggestionRanker = new SuggestionRanker();
         mNewTabPageManager = newTabPageManager;
         mNewTabPageManager.getSuggestionsSource().setObserver(this);
         mOfflinePageBridge = offlinePageBridge;
@@ -63,7 +65,8 @@ public void resetSections(boolean alwaysAllowEmptySections) {
                     resetSection(category, categoryStatus, alwaysAllowEmptySections);
         }
 
-        mNewTabPageManager.trackSnippetsPageImpression(categories, suggestionsPerCategory);
+        mNewTabPageManager.getSuggestionsMetricsReporter().onPageShown(
+                categories, suggestionsPerCategory);
     }
 
     /**
@@ -92,8 +95,10 @@ private int resetSection(@CategoryInt int category, @CategoryStatusEnum int cate
 
         // Create the section if needed.
         if (section == null) {
-            section = new SuggestionsSection(this, mNewTabPageManager, mOfflinePageBridge, info);
+            section = new SuggestionsSection(
+                    this, mNewTabPageManager, mSuggestionRanker, mOfflinePageBridge, info);
             mSections.put(category, section);
+            mSuggestionRanker.registerCategory(category);
             addChild(section);
         }
 
@@ -183,17 +188,6 @@ public void onFullRefreshRequired() {
      */
     private void setSuggestions(@CategoryInt int category, List<SnippetArticle> suggestions,
             @CategoryStatusEnum int status, boolean replaceExisting) {
-        // Count the number of suggestions before this category.
-        int globalPositionOffset = 0;
-        for (Map.Entry<Integer, SuggestionsSection> entry : mSections.entrySet()) {
-            if (entry.getKey() == category) break;
-            globalPositionOffset += entry.getValue().getSuggestionsCount();
-        }
-        // Assign global indices to the new suggestions.
-        for (SnippetArticle suggestion : suggestions) {
-            suggestion.mGlobalPosition = globalPositionOffset + suggestion.mPosition;
-        }
-
         mSections.get(category).setSuggestions(suggestions, status, replaceExisting);
     }
 
@@ -254,4 +248,41 @@ public boolean isEmpty() {
     SuggestionsSection getSectionForTesting(@CategoryInt int categoryId) {
         return mSections.get(categoryId);
     }
+
+    /**
+     * Attributes ranks to suggestions and related elements.
+     *
+     * Ranks here are 0-based scores attributed based on the position or loading order of the
+     * elements. See implementation for more details.
+     */
+    public static class SuggestionRanker {

[Bernhard Bauer, 2017/01/17 17:42:31]

Can we move this to a separate class? There isn't much here that requires it to
be in SectionList.

[dgn, 2017/01/17 18:46:24]

Done.

+        private final Map<Integer, Integer> mSuggestionsAddedPerSection = new LinkedHashMap<>();
+        private int mTotalAddedSuggestions;
+
+        /**
+         * Attributes a per section rank to the provided action item.
+         * @see ActionItem#getPerSectionRank()
+         */
+        public void rankItem(ActionItem actionItem, SuggestionsSection section) {

[Bernhard Bauer, 2017/01/17 17:42:31]

Can we rename these methods to rankActionItem() and rankSuggestion()?

[dgn, 2017/01/17 18:46:24]

Done.

+            if (actionItem.getPerSectionRank() != -1) return; // Item was already ranked.
+            actionItem.setRank(section.getSuggestionsCount());
+        }
+
+        /**
+         * Attributes global and per section rank to the provided suggestion.
+         * @see SnippetArticle#getPerSectionRank()
+         * @see SnippetArticle#getGlobalRank()
+         */
+        public void rankItem(SnippetArticle suggestion) {
+            int globalRank = mTotalAddedSuggestions++;
+            int perSectionRank = mSuggestionsAddedPerSection.get(suggestion.mCategory);
+            mSuggestionsAddedPerSection.put(suggestion.mCategory, perSectionRank + 1);
+
+            suggestion.setRank(perSectionRank, globalRank);
+        }
+
+        public void registerCategory(@CategoryInt int category) {
+            mSuggestionsAddedPerSection.put(category, 0);
+        }
+    }
 }