UserAgentStaticProperties.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.waveprotocol.wave.client.common.util;

import com.google.gwt.core.client.GWT;

/**
 * Class to allow conditional compilation for different user agents.
 *
 * All methods should return values that are known at compile time.
 *  *
 * TODO(user): Should this ever be thrown in for free with GWT, rather use
 * their approach. A relevant thread is:
 * http://groups.google.com/group/Google-Web-Toolkit-Contributors/browse_thread/thread/6745dee7a85eb585/bd58d1a9f2344b34
 *
 * FIXME: GWT superdev recompilation fails when this class is abstract
 *
 */
public class UserAgentStaticProperties {

  static UserAgentStaticProperties get() {
    return INSTANCE;
  }

  private static final UserAgentStaticProperties INSTANCE = createInstance();

  /**
   * Creates an instance of UserAgent.
   *
   * NOTE(danilatos): This method is designed to be statically evaluable by
   *                   the compiler, such that the compiler can determine that
   *                   only one subclass of UserAgent is ever used within a
   *                   given permutation. This is possible because
   *                   GWT.isClient() is replaced with true by the compiler,
   *                   even though it is executed normally in unit tests.
   *                   Testing the return value of GWT.create() is not adequate
   *                   because only boolean values can be statically evaluated
   *                   by the compiler at this time.
   *
   * @return an instance of UserAgent.
   */
  private static UserAgentStaticProperties createInstance() {
    if (GWT.isClient()) {
      return GWT.create(UserAgentStaticProperties.class);
    } else {
      return new FirefoxImpl();
    }
  }

  final boolean isWebkit() {
    return isSafari() || isMobileWebkit();
  }

  /**
   * @return true iff the user agent uses mobile webkit
   */
  final boolean isMobileWebkit() {
    return isAndroid() || isIPhone();
  }

  // Default instance methods: most return false, since they are intended to be overriden.
  boolean isSafari()  { return false; }
  boolean isFirefox() { return false; }
  boolean isIE()      { return false; }
  boolean isAndroid() { return false; }
  boolean isIPhone()  { return false; }

  // NOTE(user): Created via deferred binding
  public static class SafariImpl extends UserAgentStaticProperties {
    @Override
    protected boolean isSafari() {
      return true;
    }
  }

  // NOTE(user): Created via deferred binding
  public static class FirefoxImpl extends UserAgentStaticProperties {
    @Override
    protected boolean isFirefox() {
      return true;
    }
  }

  // NOTE(user): Created via deferred binding
  public static class IEImpl extends UserAgentStaticProperties {
    @Override
    protected boolean isIE() {
      return true;
    }
  }

  // NOTE(user): Created via deferred binding
  public static class AndroidImpl extends UserAgentStaticProperties {
    @Override
    protected boolean isAndroid() {
      return true;
    }
  }

  // NOTE(user): Created via deferred binding
  public static class IPhoneImpl extends UserAgentStaticProperties {
    @Override
    protected boolean isIPhone() {
      return true;
    }
  }
}