content: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License
   */
  
  package android.location;
  
  import android.annotation.NonNull;
  import android.content.Context;
  import android.os.Handler;
  import android.os.RemoteException;
  import android.util.Log;
  
  import com.android.internal.util.Preconditions;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * A base handler class to manage transport and local listeners.
   *
   * @hide
   */
  abstract class LocalListenerHelper<TListener> {
      private final HashMap<TListener, Handler> mListeners = new HashMap<>();
  
      private final String mTag;
      private final Context mContext;
  
      protected LocalListenerHelper(Context context, String name) {
          Preconditions.checkNotNull(name);
          mContext = context;
          mTag = name;
      }
  
      /**
       * Adds a {@param listener} to the list of listeners on which callbacks will be executed. The
       * execution will happen on the {@param handler} thread or alternatively in the callback thread
       * if a  {@code null} handler value is passed.
       */
      public boolean add(@NonNull TListener listener, Handler handler) {
          Preconditions.checkNotNull(listener);
          synchronized (mListeners) {
              // we need to register with the service first, because we need to find out if the
              // service will actually support the request before we attempt anything
              if (mListeners.isEmpty()) {
                  boolean registeredWithService;
                  try {
                      registeredWithService = registerWithServer();
                  } catch (RemoteException e) {
                      Log.e(mTag, "Error handling first listener.", e);
                      return false;
                  }
                  if (!registeredWithService) {
                      Log.e(mTag, "Unable to register listener transport.");
                      return false;
                  }
              }
              if (mListeners.containsKey(listener)) {
                  return true;
              }
              mListeners.put(listener, handler);
              return true;
          }
      }
  
      public void remove(@NonNull TListener listener) {
          Preconditions.checkNotNull(listener);
          synchronized (mListeners) {
              boolean removed = mListeners.containsKey(listener);
              mListeners.remove(listener);
              boolean isLastRemoved = removed && mListeners.isEmpty();
              if (isLastRemoved) {
                  try {
                      unregisterFromServer();
                  } catch (RemoteException e) {
                      Log.v(mTag, "Error handling last listener removal", e);
                  }
              }
          }
      }
  
      protected abstract boolean registerWithServer() throws RemoteException;
      protected abstract void unregisterFromServer() throws RemoteException;
  
      protected interface ListenerOperation<TListener> {
          void execute(TListener listener) throws RemoteException;
      }
  
      protected Context getContext() {
          return mContext;
      }
  
      private void executeOperation(ListenerOperation<TListener> operation, TListener listener) {
          try {
              operation.execute(listener);
          } catch (RemoteException e) {
              Log.e(mTag, "Error in monitored listener.", e);
              // don't return, give a fair chance to all listeners to receive the event
          }
      }
  
      protected void foreach(final ListenerOperation<TListener> operation) {
          Collection<Map.Entry<TListener, Handler>> listeners;
          synchronized (mListeners) {
              listeners = new ArrayList<>(mListeners.entrySet());
          }
          for (final Map.Entry<TListener, Handler> listener : listeners) {
              if (listener.getValue() == null) {
                  executeOperation(operation, listener.getKey());
              } else {
                  listener.getValue().post(new Runnable() {
                      @Override
                      public void run() {
                          executeOperation(operation, listener.getKey());
                      }
                  });
              }
          }
      }
  }
  