/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2010 Sun Microsystems, Inc.
 * Portions Copyright 2011-2016 ForgeRock AS.
 */
package org.opends.server.api;

import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import org.forgerock.opendj.ldap.DN;

/**
 * The DITCacheMap class implements custom Map for structural storage of
 * arbitrary objects in Directory Information Tree (DIT) like structure.
 * <p>
 * This Map intended usage is for caching various server objects which can be
 * subject to subtree operations like retrieval or removal of all objects under
 * a specific DN. While using a regular Map it would require the entire Map
 * iteration to achieve, this Map implementation maintains such internal
 * structure that subtree operations are more efficient and do not require
 * iterations over the entire map, instead additional subtree operations methods
 * are provided by this Map to do just that.
 * <p>
 * API wise it behaves exactly like a regular Map implementation except for
 * providing additional subtree methods. All required linkage and structuring is
 * performed within this Map implementation itself and not exposed via the API
 * in any way. For example, putting these key/value pairs:
 *
 * <pre>
 * cn=Object1,ou=Objects,dc=example,dc=com : object1
 * cn=Object2,ou=Objects,dc=example,dc=com : object2
 * cn=Object3,ou=Objects,dc=example,dc=com : object3
 * </pre>
 *
 * then invoking a subtree method on this Map with any of these keys:
 *
 * <pre>
 * ou=Objects,dc=example,dc=com
 * dc=example,dc=com
 * dc=com
 * </pre>
 *
 * would bring all three objects previously stored in this map into subtree
 * operation scope. Standard Map API methods can only work with the objects
 * previously stored in this map explicitly.
 * <p>
 * Note that this Map implementation is not synchronized.
 *
 * @param <T>
 *          arbitrary object type.
 */
public final class DITCacheMap<T> extends AbstractMap<DN,T>
{
  /**
   * Node class for object storage and
   * linking to any subordinate nodes.
   * @param <T> arbitrary storage object.
   */
  private static final class Node<T>
  {
    /** Node DN. */
    DN dn;
    /**
     * Storage object or null if this node exist
     * only to support the DIT like structuring.
     */
    T element;
    /** Parent. */
    Node<T> parent;
    /** First child. */
    Node<T> child;
    /** Next sibling. */
    Node<T> next;
    /** Previous sibling. */
    Node<T> previous;

    /** {@inheritDoc} */
    @Override
    public String toString()
    {
      if (element != null)
      {
        return "node(" + element + ")";
      }
      else
      {
        return "glue";
      }
    }
  }

  /** Map size reflecting only nodes containing non empty elements. */
  private int size;

  /** Backing Map implementation. */
  private final Map<DN,Node<T>> ditCacheMap = new HashMap<>();

  /** Default constructor. */
  public DITCacheMap()
  {
  }

  /**
   * Constructs a new DITCacheMap from a given Map.
   * @param m existing Map to construct new
   *          DITCacheMap from.
   */
  public DITCacheMap(Map<? extends DN, ? extends T> m)
  {
    this.putAll(m);
  }

  /** {@inheritDoc} */
  @Override
  public int size()
  {
    return size;
  }

  /** {@inheritDoc} */
  @Override
  public boolean isEmpty()
  {
    return ditCacheMap.isEmpty();
  }

  /** {@inheritDoc} */
  @Override
  public boolean containsKey(Object key)
  {
    return get(key) != null;
  }

  /** {@inheritDoc} */
  @Override
  public boolean containsValue(Object value)
  {
    for (Node<T> node : ditCacheMap.values())
    {
      if (node.element != null && node.element.equals(value))
      {
        return true;
      }
    }
    return false;
  }

  /** {@inheritDoc} */
  @Override
  public T get(Object key)
  {
    Node<T> node = ditCacheMap.get(key);
    return node != null ? node.element : null;
  }

  /**
   * Returns a set of stored objects subordinate to subtree DN.
   * @param key subtree DN.
   * @return collection of stored objects subordinate to subtree DN.
   */
  public Collection<T> getSubtree(DN key)
  {
    return new DITSubtreeSet(key);
  }

  /** {@inheritDoc} */
  @Override
  public T put(DN key, T value)
  {
    final Node<T> existingNode = ditCacheMap.get(key);
    if (existingNode != null)
    {
      final T returnValue = existingNode.element;
      existingNode.element = value;
      return returnValue;
    }

    Node<T> node = new Node<>();
    node.dn = key;
    node.element = value;
    node.parent = null;
    node.child = null;
    node.next = null;
    node.previous = null;

    ditCacheMap.put(key, node);
    size++;

    // Update parent hierarchy.
    for (DN parentDN = key.parent();
         parentDN != null;
         parentDN = parentDN.parent())
    {
      final Node<T> parentNode = ditCacheMap.get(parentDN);

      if (parentNode == null)
      {
        // Add glue node.
        final Node<T> newParentNode = new Node<>();
        newParentNode.dn = parentDN;
        newParentNode.element = null;
        newParentNode.parent = null;
        newParentNode.child = node;
        newParentNode.next = null;
        newParentNode.previous = null;
        ditCacheMap.put(parentDN, newParentNode);
        node.parent = newParentNode;
        node = newParentNode;
      }
      else
      {
        if (parentNode.child != null)
        {
          Node<T> lastNode = parentNode.child;
          while (lastNode.next != null)
          {
            lastNode = lastNode.next;
          }
          node.previous = lastNode;
          lastNode.next = node;
        }
        else
        {
          parentNode.child = node;
        }
        node.parent = parentNode;
        break;
      }
    }
    return null;
  }

  /** {@inheritDoc} */
  @Override
  public T remove(Object key)
  {
    final DN dn = (DN) key;
    final Node<T> node = ditCacheMap.get(dn);
    if (node == null)
    {
      return null;
    }

    final T returnValue = node.element;
    if (returnValue == null)
    {
      return null;
    }

    // Remove element from DIT.
    size--;
    node.element = null;

    if (node.child == null)
    {
      // This node is now glue, so remove it completely and fix up
      // any other nodes which reference it.
      ditCacheMap.remove(dn);
      fixNodeReferences(node);
    }

    return returnValue;
  }



  /**
   * Remove references to a node after it has been removed.
   * @param node The node which has just been removed.
   */
  private void fixNodeReferences(Node<T> node)
  {
    while (true)
    {
      // Fix siblings.
      final Node<T> nextNode = node.next;
      final Node<T> previousNode = node.previous;

      if (nextNode != null)
      {
        nextNode.previous = previousNode;
      }

      if (previousNode != null)
      {
        previousNode.next = nextNode;
      }

      // Fix parent, if it exists.
      final Node<T> parentNode = node.parent;
      if (parentNode == null)
      {
        // Reached the top of the DIT, so no parents to fix.
        break;
      }

      if (parentNode.child != node)
      {
        // The parent references another sibling and does not need fixing.
        break;
      }

      if (nextNode != null)
      {
        // Update child pointer and return.
        parentNode.child = nextNode;
        break;
      }

      if (parentNode.element != null)
      {
        // Parent node is still needed as it contains data.
        break;
      }

      // The parent node is glue so remove it.
      ditCacheMap.remove(parentNode.dn);

      // Smash pointers.
      node.parent = null;
      node.previous = null;
      node.next = null;

      // Continue up tree.
      node = parentNode;
    }
  }



  /**
   * Returns {@code true} if there are stored objects subordinate to subtree DN.
   * @param key subtree DN.
   * @return {@code true} if there are stored objects subordinate to subtree DN.
   */
  public boolean containsSubtree(DN key)
  {
    return ditCacheMap.containsKey(key);
  }



  /**
   * Removes a set of stored objects subordinate to subtree DN.
   * @param key subtree DN.
   * @param values collection for removed objects subordinate
   *               to subtree DN or <code>null</code>.
   * @return <code>true</code> on success or <code>false</code> otherwise.
   */
  public boolean removeSubtree(DN key, Collection<? super T> values)
  {
    final Node<T> node = ditCacheMap.remove(key);
    if (node != null)
    {
      // Fix up sibling and parent references.
      fixNodeReferences(node);

      // Collect all elements and update the size.
      adjustSizeAndCollectElements(node, values);
      return true;
    }
    return false;
  }



  /**
   * Iterate through detached subtree counting and collecting any elements.
   *
   * @param node
   *          The node to be collected.
   * @param values
   *          Collection in which to put elements.
   */
  private void adjustSizeAndCollectElements(final Node<T> node,
      Collection<? super T> values)
  {
    if (node.element != null)
    {
      if (values != null)
      {
        values.add(node.element);
      }
      node.element = null;
      size--;
    }

    // Repeat for each child.
    Node<T> child = node.child;
    while (child != null)
    {
      final Node<T> next = child.next;
      adjustSizeAndCollectElements(child, values);
      child = next;
    }

    // Smash pointers.
    node.parent = null;
    node.child = null;
    node.previous = null;
    node.next = null;

    // Remove node from map.
    ditCacheMap.remove(node.dn);
  }



  /** {@inheritDoc} */
  @Override
  public void putAll(Map<? extends DN, ? extends T> m)
  {
    for (Entry<? extends DN, ? extends T> entry : m.entrySet())
    {
      put(entry.getKey(), entry.getValue());
    }
  }

  /** {@inheritDoc} */
  @Override
  public void clear()
  {
    ditCacheMap.clear();
    size = 0;
  }

  /** {@inheritDoc} */
  @Override
  public Set<Entry<DN, T>> entrySet()
  {
    return new DITCacheEntrySet();
  }

  /** EntrySet class implementation for the DITCacheMap. */
  private class DITCacheEntrySet extends AbstractSet<Entry<DN, T>>
  {
    /** Iterator class implementation for the DITCacheEntrySet. */
    private class EntryIterator implements Iterator<Entry<DN, T>>
    {
      private Iterator<Entry<DN, Node<T>>> ditCacheMapIterator;
      private Entry<DN, Node<T>> currentEntry;
      private Entry<DN, Node<T>> nextEntry;
      private boolean hasNext;

      /** Default constructor. */
      public EntryIterator()
      {
        ditCacheMapIterator = ditCacheMap.entrySet().iterator();
        currentEntry = null;
        nextEntry = null;
        hasNext = false;
      }

      /** {@inheritDoc} */
      @Override
      public boolean hasNext()
      {
        if (hasNext)
        {
          return true;
        }
        while (ditCacheMapIterator.hasNext())
        {
          Entry<DN, Node<T>> entry = ditCacheMapIterator.next();
          Node<T> node = entry.getValue();
          if (node != null && node.element != null)
          {
            nextEntry = entry;
            hasNext = true;
            return true;
          }
        }
        nextEntry = null;
        return false;
      }

      /** {@inheritDoc} */
      @Override
      public Entry<DN, T> next()
      {
        if (nextEntry != null)
        {
          Node<T> node = nextEntry.getValue();
          currentEntry = nextEntry;
          nextEntry = null;
          hasNext = false;
          return new DITCacheMapEntry(node.dn, node.element);
        }
        while (ditCacheMapIterator.hasNext())
        {
          Entry<DN, Node<T>> entry = ditCacheMapIterator.next();
          Node<T> node = entry.getValue();
          if (node != null && node.element != null)
          {
            currentEntry = entry;
            hasNext = false;
            return new DITCacheMapEntry(node.dn, node.element);
          }
        }
        throw new NoSuchElementException();
      }

      /** {@inheritDoc} */
      @Override
      public void remove()
      {
        if (currentEntry != null)
        {
          Entry<DN, Node<T>> oldIteratorEntry = null;
          if (hasNext())
          {
            oldIteratorEntry = nextEntry;
          }
          if (DITCacheMap.this.remove(currentEntry.getKey()) != null)
          {
            ditCacheMapIterator = ditCacheMap.entrySet().iterator();
            currentEntry = null;
            nextEntry = null;
            hasNext = false;
            while (hasNext())
            {
              Entry<DN, T> newIteratorEntry = next();
              if (oldIteratorEntry != null
                  && oldIteratorEntry.getKey().equals(newIteratorEntry.getKey())
                  && oldIteratorEntry.getValue().element.equals(newIteratorEntry.getValue()))
              {
                nextEntry = currentEntry;
                hasNext = true;
                return;
              }
            }
            currentEntry = null;
            nextEntry = null;
            hasNext = false;
            return;
          }
        }
        throw new IllegalStateException();
      }
    }

    /** {@inheritDoc} */
    @Override
    public int size()
    {
      return DITCacheMap.this.size();
    }

    /** {@inheritDoc} */
    @Override
    public Iterator<Entry<DN, T>> iterator()
    {
      return new EntryIterator();
    }
  }

  /** Map.Entry class implementation for the DITCacheMap. */
  private class DITCacheMapEntry implements Map.Entry<DN, T>
  {
    private DN key;
    private T  value;

    /**
     * Constructs a new DITCacheMapEntry
     * with given key and value.
     * @param key Map.Entry key.
     * @param value Map.Entry value.
     */
    public DITCacheMapEntry(DN key, T value)
    {
      this.key = key;
      this.value = value;
    }

    /** {@inheritDoc} */
    @Override
    public DN getKey()
    {
      return key;
    }

    /** {@inheritDoc} */
    @Override
    public T getValue()
    {
      return value;
    }

    /** {@inheritDoc} */
    @Override
    public T setValue(T value)
    {
      Node<T> node = ditCacheMap.get(key);
      T oldValue = this.value;
      node.element = value;
      this.value = value;
      return oldValue;
    }
  }

  /** SubtreeSet class implementation. */
  private class DITSubtreeSet extends AbstractSet<T>
  {
    /** Set key. */
    private DN key;

    /**
     * Keyed constructor.
     * @param key to construct
     *        this set from.
     */
    public DITSubtreeSet(DN key)
    {
      this.key = key;
    }

    /** Iterator class implementation for SubtreeSet. */
    private class SubtreeSetIterator implements Iterator<T>
    {
      /** Iterator key. */
      private DN key;

      /** Iterator root node. */
      private Node<T> rootNode;

      /** Iterator current node. */
      private Node<T> node;

      /** Default constructor. */
      public SubtreeSetIterator()
      {
        this.key = DITSubtreeSet.this.key;
        rootNode = ditCacheMap.get(this.key);
        node = rootNode;
      }

      /**
       * Keyed constructor.
       * @param key to cue this
       *        iterator from.
       */
      public SubtreeSetIterator(DN key)
      {
        this.key = key;
        rootNode = ditCacheMap.get(this.key);
        node = rootNode;
      }

      @Override
      public boolean hasNext()
      {
        if (rootNode != null)
        {
          if (node == rootNode && rootNode.element != null)
          {
            return true;
          }
          while (node != null)
          {
            if (node.element != null)
            {
              return true;
            }
            if (node.child != null)
            {
              node = node.child;
            }
            else
            {
              while (node.next == null && node.parent != rootNode)
              {
                node = node.parent;
              }
              node = node.next;
            }
          }
        }
        return false;
      }

      @Override
      public T next()
      {
        T element = null;

        if (rootNode != null)
        {
          if (node == rootNode)
          {
            node = rootNode.child;
            if (rootNode.element != null)
            {
              return rootNode.element;
            }
          }
          while (node != null)
          {
            element = node.element;
            if (node.child != null)
            {
              node = node.child;
            }
            else
            {
              while (node.next == null && node.parent != rootNode)
              {
                node = node.parent;
              }
              node = node.next;
            }
            if (element != null)
            {
              return element;
            }
          }
        }
        throw new NoSuchElementException();
      }

      @Override
      public void remove()
      {
        throw new UnsupportedOperationException();
      }
    }

    @Override
    public Iterator<T> iterator()
    {
      return new SubtreeSetIterator();
    }

    @Override
    public boolean isEmpty()
    {
      return !(new SubtreeSetIterator(this.key).hasNext());
    }

    @Override
    public int size()
    {
      int size = 0;

      Iterator<T> iterator = new SubtreeSetIterator(this.key);
      while (iterator.hasNext())
      {
        iterator.next();
        size++;
      }

      return size;
    }
  }

  /**
   * Returns the size of the internal map. Used for testing purposes only.
   *
   * @return The size of the internal map.
   */
  int getMapSize()
  {
    return ditCacheMap.size();
  }
}