/**
 * Copyright 2011 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 org.waveprotocol.wave.client.scroll;

import com.google.common.base.Preconditions;
import com.google.gwt.dom.client.Element;

import org.waveprotocol.wave.client.common.util.DomHelper;
import org.waveprotocol.wave.client.common.util.Measurer;
import org.waveprotocol.wave.client.common.util.MeasurerInstance;

/**
 * Reveals the scrolling capabilities of a DOM element.
 *
 */
public final class DomScrollPanel implements ScrollPanel<Element> {
  private final Element element;
  private final Measurer measurer;

  DomScrollPanel(Element element, Measurer measurer) {
    this.element = element;
    this.measurer = measurer;
  }

  /**
   * Reveals {@code e} as a scroll panel. It is assumed that the given element
   * has appropriate CSS constraints that make it scrollable.
   */
  public static DomScrollPanel create(Element e) {
    return new DomScrollPanel(e, MeasurerInstance.get());
  }

  @Override
  public Extent getViewport() {
    int top = element.getScrollTop();
    return Extent.of(top, top + measurer.height(element));
  }

  @Override
  public Extent getContent() {
    Element first = element.getFirstChildElement();
    Element last = DomHelper.getLastChildElement(element);
    Preconditions.checkNotNull(first, "No content");
    int top = element.getScrollTop();
    return Extent.of(measurer.top(element, first) + top, measurer.bottom(element, last) + top);
  }

  @Override
  public Extent extentOf(Element target) {
    int top = element.getScrollTop();
    return Extent.of(measurer.top(element, target) + top, measurer.bottom(element, target) + top);
  }

  @Override
  public void moveTo(double location) {
    element.setScrollTop((int) location);
  }
}