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// 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 streamer;

import java.util.Set;

/**
 * Element is for processing of data. It has one or more contact pads, which can
 * be wired with other elements using links.
 */
public interface Element {

  /**
   * Name of pad for standard input. Should be set in all elements except pure
   * sinks.
   */
  public static final String STDIN = "stdin";

  /**
   * Name of pad for standard output. Should be set in all elements except pure
   * sources.
   */
  public static final String STDOUT = "stdout";

  /**
   * Get link connected to given pad.
   * 
   * @param padName
   *          Standard pads are "stdin" and "stdout".
   */
  Link getLink(String padName);

  /**
   * Get pads of this element.
   */
  Set<String> getPads(Direction direction);

  /**
   * Connect link to given pad.
   * 
   * @param padName
   *          a pad name. Standard pads are "stdin" and "stdout".
   */
  void setLink(String padName, Link link, Direction direction);

  /**
   * Disconnect link from given pad.
   * 
   * @param padName
   *          Standard pads are "stdin" and "stdout".
   */
  void dropLink(String padName);

  /**
   * Pull data from element and handle it. Element should ask one of it input
   * pads for data, handle data and push result to it sink(s), if any.
   * 
   * @param block
   *          block until data will be available, or do a slight delay at least,
   *          when data is not available
   */
  void poll(boolean block);

  /**
   * Handle incoming data.
   * 
   * @param buf
   *          a data
   * @param link
   *          TODO
   */
  void handleData(ByteBuffer buf, Link link);

  /**
   * Handle event.
   * 
   * @param event
   *          an event
   * @param direction
   *          if IN, then send event to input pads, when OUT, then send to
   *          output pads
   */
  void handleEvent(Event event, Direction direction);

  /**
   * Get element ID.
   */
  String getId();

  /**
   * Validate element: check is all required pads are connected.
   */
  void validate();

  /**
   * Drop link.
   * 
   * @param link a link to drop
   */
  void dropLink(Link link);

  /**
   * Drop existing link and replace it by new link.
   */
  void replaceLink(Link existingLink, Link newLink);
}