/**
 * 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;


/**
 * Defines UI scrolling actions on a scroll panel.
 *
 * @author hearnden@google.com (David Hearnden)
 */
public final class ScrollController {
  private final ScrollPanel<?> scroller;

  /**
   * Creates a scroll controller.
   */
  ScrollController(ScrollPanel<?> scroller) {
    this.scroller = scroller;
  }

  void pageUp() {
    Extent viewport = scroller.getViewport();
    double target = Math.max(0, viewport.getStart() - viewport.getSize());
    scroller.moveTo(target);
  }

  void pageDown() {
    Extent viewport = scroller.getViewport();
    double target = Math.min(scroller.getContent().getEnd(), viewport.getEnd());
    scroller.moveTo(target);
  }

  void home() {
    scroller.moveTo(0);
  }

  void end() {
    Extent content = scroller.getContent();
    Extent viewport = scroller.getViewport();
    scroller.moveTo(content.getEnd() - viewport.getSize());
  }
}