/*
 * Copyright 2010 Google Inc.
 *
 * 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 com.google.gwt.event.dom.client;

import com.google.gwt.core.client.GWT;
import com.google.gwt.core.client.JsArray;
import com.google.gwt.dom.client.Touch;
import com.google.gwt.event.shared.EventHandler;

/**
 * Abstract class representing touch events.
 *
 * See {@link <a href="http://developer.apple.com/library/safari/documentation/UserExperience/Reference/TouchEventClassReference/TouchEvent/TouchEvent.html">Safari Touch Event Documentation</a>}
 * @param <H> handler type
 */
public abstract class TouchEvent<H extends EventHandler>
    extends HumanInputEvent<H> {

  /**
   * Dectector for browser support for touch events.
   */
  private static class TouchSupportDetector {

    private final boolean isSupported = detectTouchSupport();

    public boolean isSupported() {
      return isSupported;
    }

    private native boolean detectTouchSupport() /*-{
      var elem = document.createElement('div');
      elem.setAttribute('ontouchstart', 'return;');
      return (typeof elem.ontouchstart) == "function";
    }-*/;
  }

  /**
   * Detector for browsers that do not support touch events.
   */
  @SuppressWarnings("unused")
  private static class TouchSupportDetectorNo extends TouchSupportDetector {
    @Override
    public boolean isSupported() {
      return false;
    }
  }

  /**
   * The implementation singleton.
   */
  private static TouchSupportDetector impl;

  /**
   * Runtime check for whether touch scrolling is supported in this browser. Returns true if touch
   * events are supported but touch based scrolling is not natively supported.
   * 
   * @return true if touch events are supported, false if not
   */
  public static boolean isSupported() {
    if (impl == null) {
      impl = GWT.create(TouchSupportDetector.class);
    }
    return impl.isSupported();
  }

  /**
   * Get an array of {@link Touch touches} which have changed since the last
   * touch event fired. Note, that for {@link TouchEndEvent touch end events},
   * the touch which has just ended will not be present in the array. Moreover,
   * if the touch which just ended was the last remaining touch, then a zero
   * length array will be returned.
   *
   * @return an array of touches
   */
  public JsArray<Touch> getChangedTouches() {
    return getNativeEvent().getChangedTouches();
  }

  /**
   * Get an array of {@link Touch touches} all touch which originated at the
   * same target as the current touch event. Note, that for {@link TouchEndEvent
   * touch end events}, the touch which has just ended will not be present in
   * the array. Moreover, if the touch which just ended was the last remaining
   * touch, then a zero length array will be returned.
   *
   * @return an array of touches
   */
  public JsArray<Touch> getTargetTouches() {
    return getNativeEvent().getTargetTouches();
  }

  /**
   * Get an array of all current {@link Touch touches}. Note, that for
   * {@link TouchEndEvent touch end events}, the touch which has just ended will
   * not be present in the array. Moreover, if the touch which just ended was
   * the last remaining touch, then a zero length array will be returned.
   *
   * @return an array of touches
   */
  public JsArray<Touch> getTouches() {
    return getNativeEvent().getTouches();
  }
}