Cache client checks for android.keystore

Only certain actions modify the state of android.keystore on the
server. The keystore can only change if a new one is imported, the
current keystore is deleted, or when no keystore exists but the user
builds an app. However, this is not reflected in the flow control of
App Inventor. Switching between projects, for example, will check for
the state of android.keystore even though this is a user file not a
project file, and the state of the android.keystore will be invariant
between projects.

This commit caches the result of checks for android.keystore to reduce
the number of round trips to the server and only rechecks when an
action may result in an update to the status or in the event an
earlier call to hasUserFile fails.

Change-Id: I65df499d509ea7098f6b349d0da09cdaea84dd08

appinventor/appengine/src/com/google/appinventor/client/TopToolbar.java

@@ -124,6 +124,19 @@ public class TopToolbar extends Composite {
   public DropDownButton adminDropDown;
 
   private boolean isReadOnly;
+  /**
+   * This flag is set to true when a check for the android.keystore file is in progress.
+   */
+  private volatile boolean isKeystoreCheckPending = false;
+  /**
+   * This flag is set to true when a call to {@link #updateKeystoreFileMenuButtons(boolean)} has
+   * returned and the value was cached.
+   */
+  private volatile boolean isKeystoreCached = false;
+  /**
+   * This flag is the cached result of an earlier check for android.keystore.
+   */
+  private volatile boolean isKeystorePresent = false;
 
   public TopToolbar() {
     /*
@@ -675,7 +688,12 @@ public class TopToolbar extends Composite {
                     new OdeAsyncCallback<Void>(errorMessage) {
                       @Override
                       public void onSuccess(Void result) {
-                        updateKeystoreFileMenuButtons();
+                        // The android.keystore shouldn't exist at this point, so reset cached values.
+                        isKeystoreCached = true;
+                        isKeystorePresent = false;
+                        isKeystoreCheckPending = false;
+                        fileDropDown.setItemEnabled(MESSAGES.deleteKeystoreMenuItem(), false);
+                        fileDropDown.setItemEnabled(MESSAGES.downloadKeystoreMenuItem(), false);
                       }
                     });
               }
@@ -944,7 +962,7 @@ public class TopToolbar extends Composite {
       buildDropDown.setItemEnabled(MESSAGES.showBarcodeMenuItem(), true);
       buildDropDown.setItemEnabled(MESSAGES.downloadToComputerMenuItem(), true);
     }
-    updateKeystoreFileMenuButtons();
+    updateKeystoreFileMenuButtons(true);
   }
 
   /**
@@ -955,6 +973,8 @@ public class TopToolbar extends Composite {
         new AsyncCallback<Boolean>() {
           @Override
           public void onSuccess(Boolean keystoreFileExists) {
+            isKeystoreCached = true;
+            isKeystorePresent = keystoreFileExists;
             fileDropDown.setItemEnabled(MESSAGES.deleteKeystoreMenuItem(), keystoreFileExists);
             fileDropDown.setItemEnabled(MESSAGES.downloadKeystoreMenuItem(), keystoreFileExists);
           }
@@ -968,6 +988,45 @@ public class TopToolbar extends Composite {
         });
   }
 
+  /**
+   * Enables or disables buttons based on whether the user has an android.keystore file. If the
+   * useCache parameter is true, then the last value returned from the UserInfoService is used.
+   * Otherwise, the behavior is identical to {@link #updateKeystoreFileMenuButtons()}.
+   *
+   * @param useCache true if a cached value of a previous call is acceptable.
+   */
+  public void updateKeystoreFileMenuButtons(boolean useCache) {
+    if (useCache && isKeystoreCheckPending) {
+      return;
+    }
+    AsyncCallback<Boolean> callback = new AsyncCallback<Boolean>() {
+      @Override
+      public void onSuccess(Boolean keystoreFileExists) {
+        isKeystoreCached = true;
+        isKeystorePresent = keystoreFileExists;
+        isKeystoreCheckPending = false;
+        fileDropDown.setItemEnabled(MESSAGES.deleteKeystoreMenuItem(), keystoreFileExists);
+        fileDropDown.setItemEnabled(MESSAGES.downloadKeystoreMenuItem(), keystoreFileExists);
+      }
+
+      @Override
+      public void onFailure(Throwable caught) {
+        // Enable the MenuItems. If they are clicked, we'll check again if the keystore exists.
+        isKeystoreCached = false;
+        isKeystorePresent = true;
+        isKeystoreCheckPending = false;
+        fileDropDown.setItemEnabled(MESSAGES.deleteKeystoreMenuItem(), true);
+        fileDropDown.setItemEnabled(MESSAGES.downloadKeystoreMenuItem(), true);
+      }
+    };
+    if (useCache && isKeystoreCached) {
+      callback.onSuccess(isKeystorePresent);
+    } else {
+      isKeystoreCheckPending = true;
+      Ode.getInstance().getUserInfoService().hasUserFile(StorageUtil.ANDROID_KEYSTORE_FILENAME,
+          callback);
+    }
+  }
 
   //Admin commands
   private static class DownloadUserSourceAction implements Command {