Add TabSuggestionsObserver and start passing messages from Orchestrator

TabSuggestionsObserver is used by the orchestrator to broadcast
messages about new suggestion results and when tabContexts
become invalidated.

Bug: 1017896
Change-Id: I5ba99bd920a8fefccf94a3b7137e7dff8bb1074c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879600
Commit-Queue: David Maunder <davidjm@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Mei Liang <meiliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712108}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestions.java

@@ -4,9 +4,19 @@
 
 package org.chromium.chrome.browser.tasks.tab_management.suggestions;
 
-import java.util.List;
-
 /**
  * Interface for the Tab Suggestions framework.
  */
-public interface TabSuggestions { List<TabSuggestion> getSuggestions(TabContext tabContext); }
+public interface TabSuggestions {
+    /**
+     * Adds an observer
+     * @param tabSuggestionsObserver observer which is notified when new suggestions are available
+     */
+    void addObserver(TabSuggestionsObserver tabSuggestionsObserver);
+
+    /**
+     * Removes an observer
+     * @param tabSuggestionsObserver observer which is notified when new suggestions are available
+     */
+    void removeObserver(TabSuggestionsObserver tabSuggestionsObserver);
+}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestionsObserver.java

+// Copyright 2019 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.
+
+package org.chromium.chrome.browser.tasks.tab_management.suggestions;
+
+import java.util.List;
+
+/**
+ * Observes when new Tab Suggestions become available
+ */
+public interface TabSuggestionsObserver {
+    /**
+     * Notify when we have new Tab Suggestions
+     * @param tabSuggestions tab suggestions acquired
+     */
+    void onNewSuggestion(List<TabSuggestion> tabSuggestions);
+
+    /**
+     * Notify when a {@link TabContext} is no longer valid/representative of the user's tabs.
+     */
+    void onTabSuggestionInvalidated();
+}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestionsOrchestrator.java

@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.tasks.tab_management.suggestions;
 
+import org.chromium.base.ObserverList;
 import org.chromium.chrome.browser.lifecycle.ActivityLifecycleDispatcher;
 import org.chromium.chrome.browser.lifecycle.Destroyable;
 import org.chromium.chrome.browser.tabmodel.TabModelSelector;
@@ -27,15 +28,26 @@ public class TabSuggestionsOrchestrator implements TabSuggestions, Destroyable {
     private List<TabSuggestion> mPrefetchedResults = new LinkedList<>();
     private TabContext mPrefetchedTabContext;
     private TabModelSelector mTabModelSelector;
+    private ObserverList<TabSuggestionsObserver> mTabSuggestionsObservers;
+    private int mRemainingFetchers;
 
     public TabSuggestionsOrchestrator(
             TabModelSelector selector, ActivityLifecycleDispatcher activityLifecycleDispatcher) {
         mTabModelSelector = selector;
         mTabSuggestionsFetchers = new LinkedList<>();
         mTabSuggestionsFetchers.add(new TabSuggestionsClientFetcher());
+        mTabSuggestionsObservers = new ObserverList<>();
         mTabContextObserver = new TabContextObserver(selector) {
             @Override
             public void onTabContextChanged(@TabContextChangeReason int changeReason) {
+                synchronized (mPrefetchedResults) {
+                    if (mPrefetchedTabContext != null) {
+                        for (TabSuggestionsObserver tabSuggestionsObserver :
+                                mTabSuggestionsObservers) {
+                            tabSuggestionsObserver.onTabSuggestionInvalidated();
+                        }
+                    }
+                }
                 prefetchSuggestions();
             }
         };
@@ -43,16 +55,6 @@ public class TabSuggestionsOrchestrator implements TabSuggestions, Destroyable {
         activityLifecycleDispatcher.register(this);
     }
 
-    @Override
-    public List<TabSuggestion> getSuggestions(TabContext tabContext) {
-        synchronized (mPrefetchedResults) {
-            if (tabContext.equals(mPrefetchedTabContext)) {
-                return aggregateResults(mPrefetchedResults);
-            }
-            return new LinkedList<>();
-        }
-    }
-
     private List<TabSuggestion> aggregateResults(List<TabSuggestion> tabSuggestions) {
         List<TabSuggestion> aggregated = new LinkedList<>();
         for (TabSuggestion tabSuggestion : tabSuggestions) {
@@ -90,10 +92,12 @@ public class TabSuggestionsOrchestrator implements TabSuggestions, Destroyable {
     protected void prefetchSuggestions() {
         TabContext tabContext = TabContext.createCurrentContext(mTabModelSelector);
         synchronized (mPrefetchedResults) {
+            mRemainingFetchers = 0;
             mPrefetchedTabContext = tabContext;
             mPrefetchedResults = new LinkedList<>();
             for (TabSuggestionsFetcher tabSuggestionsFetcher : mTabSuggestionsFetchers) {
                 if (tabSuggestionsFetcher.isEnabled()) {
+                    mRemainingFetchers++;
                     tabSuggestionsFetcher.fetch(tabContext, res -> prefetchCallback(res));
                 }
             }
@@ -102,9 +106,28 @@ public class TabSuggestionsOrchestrator implements TabSuggestions, Destroyable {
 
     private void prefetchCallback(TabSuggestionsFetcherResults suggestions) {
         synchronized (mPrefetchedResults) {
+            // If the tab context has changed since the fetchers were used,
+            // we simply ignore the result as it is no longer relevant.
             if (suggestions.tabContext.equals(mPrefetchedTabContext)) {
+                mRemainingFetchers--;
                 mPrefetchedResults.addAll(suggestions.tabSuggestions);
+                if (mRemainingFetchers == 0) {
+                    for (TabSuggestionsObserver tabSuggestionsObserver : mTabSuggestionsObservers) {
+                        tabSuggestionsObserver.onNewSuggestion(
+                                aggregateResults(mPrefetchedResults));
+                    }
+                }
             }
         }
     }
+
+    @Override
+    public void addObserver(TabSuggestionsObserver tabSuggestionsObserver) {
+        mTabSuggestionsObservers.addObserver(tabSuggestionsObserver);
+    }
+
+    @Override
+    public void removeObserver(TabSuggestionsObserver tabSuggestionsObserver) {
+        mTabSuggestionsObservers.removeObserver(tabSuggestionsObserver);
+    }
 }

chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestionsOrchestratorTest.java

@@ -32,6 +32,7 @@ import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.test.util.browser.Features;
 import org.chromium.testing.local.LocalRobolectricTestRunner;
 
+import java.util.LinkedList;
 import java.util.List;
 
 /**
@@ -87,9 +88,18 @@ public class TabSuggestionsOrchestratorTest {
         }
         TabSuggestionsOrchestrator tabSuggestionsOrchestrator =
                 new TabSuggestionsOrchestrator(mTabModelSelector, mDispatcher);
+        List<TabSuggestion> suggestions = new LinkedList<>();
+        TabSuggestionsObserver tabSuggestionsObserver = new TabSuggestionsObserver() {
+            @Override
+            public void onNewSuggestion(List<TabSuggestion> tabSuggestions) {
+                suggestions.addAll(tabSuggestions);
+            }
+
+            @Override
+            public void onTabSuggestionInvalidated() {}
+        };
+        tabSuggestionsOrchestrator.addObserver(tabSuggestionsObserver);
         tabSuggestionsOrchestrator.mTabContextObserver.mTabModelObserver.didAddTab(null, 0);
-        List<TabSuggestion> suggestions = tabSuggestionsOrchestrator.getSuggestions(
-                TabContext.createCurrentContext(mTabModelSelector));
         Assert.assertEquals(1, suggestions.size());
         Assert.assertEquals(TAB_IDS.length, suggestions.get(0).getTabsInfo().size());
         for (int idx = 0; idx < TAB_IDS.length; idx++) {
@@ -112,9 +122,17 @@ public class TabSuggestionsOrchestratorTest {
         doReturn(sTabs[0]).when(mTabModelFilter).getTabAt(eq(0));
         TabSuggestionsOrchestrator tabSuggestionsOrchestrator =
                 new TabSuggestionsOrchestrator(mTabModelSelector, mDispatcher);
+        List<TabSuggestion> suggestions = new LinkedList<>();
+        TabSuggestionsObserver tabSuggestionsObserver = new TabSuggestionsObserver() {
+            @Override
+            public void onNewSuggestion(List<TabSuggestion> tabSuggestions) {
+                suggestions.addAll(tabSuggestions);
+            }
+
+            @Override
+            public void onTabSuggestionInvalidated() {}
+        };
         tabSuggestionsOrchestrator.mTabContextObserver.mTabModelObserver.didAddTab(null, 0);
-        List<TabSuggestion> suggestions = tabSuggestionsOrchestrator.getSuggestions(
-                TabContext.createCurrentContext(mTabModelSelector));
         Assert.assertEquals(0, suggestions.size());
     }
 }

chrome/android/features/tab_ui/tab_management_java_sources.gni

@@ -17,6 +17,7 @@ public_tab_management_java_sources = [
   "//chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabSwitcher.java",
   "//chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabContext.java",
   "//chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestions.java",
+  "//chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestionsObserver.java",
   "//chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/suggestions/TabSuggestion.java",
 ]