/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
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- Redistributions of source code must retain the above copyright
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- Redistributions in binary form must reproduce the above copyright
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documentation and/or other materials provided with the distribution.

- Neither  the name  of Rice  University (RICE) nor  the names  of its
contributors may be  used to endorse or promote  products derived from
this software without specific prior written permission.

This software is provided by RICE and the contributors on an "as is"
basis, without any representations or warranties of any kind, express
or implied including, but not limited to, representations or
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********************************************************************************/

package rice.p2p.scribe;

import java.util.*;

import rice.environment.Environment;
import rice.p2p.commonapi.*;
import rice.p2p.scribe.messaging.*;

/**
 * @(#) ScribePolicy.java This interface represents a policy for Scribe, which
 * is asked whenever a child is about to be added or removed, or when the the
 * local node is about to be implicitly subscribed to a new topic.
 *
 * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
 * @author Alan Mislove
 */
public interface ScribePolicy {

  /**
   * This method is called when the newChild is about to become our child, and
   * the policy should return whether or not the child should be allowed to
   * become our child. If the length of children and clients is both 0, allowing
   * the child to join will have the effect of implicitly subscribing this node
   * the the given topic.
   *
   * @param message The subscribe message in question
   * @param clients The list of clients are are currently subscribed to this
   *      topic
   * @param children The list of children who are currently subscribed to this
   *      topic
   * @return Whether or not this child should be allowed add.
   */
  public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children);

  /**
   * This method is called when an anycast is received which is not satisfied at
   * the local node. This method should add both the parent and child nodes to
   * the anycast's to-search list, but this method allows different policies
   * concerning the order of the adding as well as selectively adding nodes.
   *
   * @param message The anycast message in question
   * @param parent Our current parent for this message's topic
   * @param children Our current children for this message's topic
   */
  public void directAnycast(AnycastMessage message, NodeHandle parent, NodeHandle[] children);

  /**
   * Informs this policy that a child was added to a topic - the topic is free
   * to ignore this upcall if it doesn't care.
   *
   * @param topic The topic to unsubscribe from
   * @param child The child that was added
   */
  public void childAdded(Topic topic, NodeHandle child);

  /**
   * Informs this policy that a child was removed from a topic - the topic is
   * free to ignore this upcall if it doesn't care.
   *
   * @param topic The topic to unsubscribe from
   * @param child The child that was removed
   */
  public void childRemoved(Topic topic, NodeHandle child);

  /**
   * The default policy for Scribe, which always allows new children to join and
   * adds children in the order in which they are provided, implicitly providing
   * a depth-first search.
   *
   * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
   * @author amislove
   */
  public static class DefaultScribePolicy implements ScribePolicy {
    /**
     * DESCRIBE THE FIELD
     */
    protected Environment environment;

    /**
     * Constructor for DefaultScribePolicy.
     *
     * @param env DESCRIBE THE PARAMETER
     */
    public DefaultScribePolicy(Environment env) {
      environment = env;
    }

    /**
     * This method always return true;
     *
     * @param message The subscribe message in question
     * @param clients The list of clients are are currently subscribed
     * @param children The list of children who are currently subscribed
     * @return True.
     */
    public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children) {
      return true;
    }

    /**
     * Simply adds the parent and children in order, which implements a
     * depth-first-search.
     *
     * @param message The anycast message in question
     * @param parent Our current parent for this message's topic
     * @param children Our current children for this message's topic
     */
    public void directAnycast(AnycastMessage message, NodeHandle parent, NodeHandle[] children) {
      if (parent != null) {
        message.addLast(parent);
      }

      // now randomize the children list
      for (int i = 0; i < children.length; i++) {
        int j = environment.getRandomSource().nextInt(children.length);
        int k = environment.getRandomSource().nextInt(children.length);
        NodeHandle tmp = children[j];
        children[j] = children[k];
        children[k] = tmp;
      }

      for (int l = 0; l < children.length; l++) {
        message.addFirst(children[l]);
      }
    }

    /**
     * Informs this policy that a child was added to a topic - the topic is free
     * to ignore this upcall if it doesn't care.
     *
     * @param topic The topic to unsubscribe from
     * @param child The child that was added
     */
    public void childAdded(Topic topic, NodeHandle child) {
    }

    /**
     * Informs this policy that a child was removed from a topic - the topic is
     * free to ignore this upcall if it doesn't care.
     *
     * @param topic The topic to unsubscribe from
     * @param child The child that was removed
     */
    public void childRemoved(Topic topic, NodeHandle child) {
    }
  }

  /**
   * An optional policy for Scribe, which allows up to a specified number of
   * children per topic.
   *
   * @version $Id: ScribePolicy.java 2551 2005-06-06 19:01:02Z jeffh $
   * @author amislove
   */
  public static class LimitedScribePolicy extends DefaultScribePolicy {

    /**
     * The number of children to allow per topic
     */
    protected int maxChildren;

    /**
     * Construtor which takes a maximum number
     *
     * @param max The maximum number of children
     * @param env DESCRIBE THE PARAMETER
     */
    public LimitedScribePolicy(int max, Environment env) {
      super(env);
      this.maxChildren = max;
    }

    /**
     * This method returns (children.length < maxChildren-1);
     *
     * @param message The subscribe message in question
     * @param clients The list of clients are are currently subscribed
     * @param children The list of children who are currently subscribed
     * @return True.
     */
    public boolean allowSubscribe(SubscribeMessage message, ScribeClient[] clients, NodeHandle[] children) {
      return (children.length < (maxChildren - 1));
    }
  }
}

