/*
 * JBoss, Home of Professional Open Source.
 * Copyright 2000 - 2008, Red Hat Middleware LLC, and individual contributors
 * as indicated by the @author tags. See the copyright.txt file in the
 * distribution for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.jboss.cache.util;

import java.io.IOException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * A HashMap that is optimized for fast shallow copies. If the copy-ctor is
 * passed another FastCopyHashMap, or clone is called on this map, the shallow
 * copy can be performed using little more than a single array copy. In order to
 * accomplish this, immutable objects must be used internally, so update
 * operations result in slightly more object churn than <code>HashMap</code>.
 *
 * Note: It is very important to use a smaller load factor than you normally
 * would for HashMap, since the implementation is open-addressed with linear
 * probing. With a 50% load-factor a get is expected to return in only 2 probes.
 * However, a 90% load-factor is expected to return in around 50 probes.
 *
 * @author Jason T. Greene
 */
public class FastCopyHashMap<K, V> extends AbstractMap<K, V> implements Map<K, V>, Cloneable, Serializable
{
   /**
    * Marks null keys.
    */
   private static final Object NULL = new Object();

   /**
    * Serialization ID
    */
   private static final long serialVersionUID = 10929568968762L;

   /**
    * Same default as HashMap, must be a power of 2
    */
   private static final int DEFAULT_CAPACITY = 8;

   /**
    * MAX_INT - 1
    */
   private static final int MAXIMUM_CAPACITY = 1 << 30;

   /**
    * 67%, just like IdentityHashMap
    */
   private static final float DEFAULT_LOAD_FACTOR = 0.67f;

   /**
    * The open-addressed table
    */
   private transient Entry<K, V>[] table;

   /**
    * The current number of key-value pairs
    */
   private transient int size;

   /**
    * The next resize
    */
   private transient int threshold;

   /**
    * The user defined load factor which defines when to resize
    */
   private final float loadFactor;

   /**
    * Counter used to detect changes made outside of an iterator
    */
   private transient int modCount;

   // Cached views
   private transient KeySet keySet;
   private transient Values values;
   private transient EntrySet entrySet;

   public FastCopyHashMap(int initialCapacity, float loadFactor)
   {
      if (initialCapacity < 0)
         throw new IllegalArgumentException("Can not have a negative size table!");

      if (initialCapacity > MAXIMUM_CAPACITY)
         initialCapacity = MAXIMUM_CAPACITY;

      if (!(loadFactor > 0F && loadFactor <= 1F))
         throw new IllegalArgumentException("Load factor must be greater than 0 and less than or equal to 1");

      this.loadFactor = loadFactor;
      init(initialCapacity, loadFactor);
   }

   @SuppressWarnings("unchecked")
   public FastCopyHashMap(Map<? extends K, ? extends V> map)
   {
      if (map instanceof FastCopyHashMap)
      {
         FastCopyHashMap<? extends K, ? extends V> fast = (FastCopyHashMap<? extends K, ? extends V>) map;
         this.table = (Entry<K, V>[]) fast.table.clone();
         this.loadFactor = fast.loadFactor;
         this.size = fast.size;
         this.threshold = fast.threshold;
      }
      else
      {
         this.loadFactor = DEFAULT_LOAD_FACTOR;
         init(map.size(), this.loadFactor);
         putAll(map);
      }
   }

   @SuppressWarnings("unchecked")
   private void init(int initialCapacity, float loadFactor)
   {
      int c = 1;
      for (; c < initialCapacity; c <<= 1) ;
      threshold = (int) (c * loadFactor);

      // Include the load factor when sizing the table for the first time
      if (initialCapacity > threshold && c < MAXIMUM_CAPACITY)
      {
         c <<= 1;
         threshold = (int) (c * loadFactor);
      }

      this.table = (Entry<K, V>[]) new Entry[c];
   }

   public FastCopyHashMap(int initialCapacity)
   {
      this(initialCapacity, DEFAULT_LOAD_FACTOR);
   }

   public FastCopyHashMap()
   {
      this(DEFAULT_CAPACITY);
   }

   // The normal bit spreader...
   private static final int hash(Object key)
   {
      int h = key.hashCode();
      h ^= (h >>> 20) ^ (h >>> 12);
      return h ^ (h >>> 7) ^ (h >>> 4);
   }

   @SuppressWarnings("unchecked")
   private static final <K> K maskNull(K key)
   {
      return key == null ? (K) NULL : key;
   }

   private static final <K> K unmaskNull(K key)
   {
      return key == NULL ? null : key;
   }

   private int nextIndex(int index, int length)
   {
      index = (index >= length - 1) ? 0 : index + 1;
      return index;
   }

   private static final boolean eq(Object o1, Object o2)
   {
      return o1 == o2 || (o1 != null && o1.equals(o2));
   }

   private static final int index(int hashCode, int length)
   {
      return hashCode & (length - 1);
   }

   public int size()
   {
      return size;
   }

   public boolean isEmpty()
   {
      return size == 0;
   }

   public V get(Object key)
   {
      key = maskNull(key);

      int hash = hash(key);
      int length = table.length;
      int index = index(hash, length);

      for (int start = index; ;)
      {
         Entry<K, V> e = table[index];
         if (e == null)
            return null;

         if (e.hash == hash && eq(key, e.key))
            return e.value;

         index = nextIndex(index, length);
         if (index == start) // Full table
            return null;
      }
   }

   public boolean containsKey(Object key)
   {
      key = maskNull(key);

      int hash = hash(key);
      int length = table.length;
      int index = index(hash, length);

      for (int start = index; ;)
      {
         Entry<K, V> e = table[index];
         if (e == null)
            return false;

         if (e.hash == hash && eq(key, e.key))
            return true;

         index = nextIndex(index, length);
         if (index == start) // Full table
            return false;
      }
   }

   public boolean containsValue(Object value)
   {
      for (Entry<K, V> e : table)
         if (e != null && eq(value, e.value))
            return true;

      return false;
   }

   public V put(K key, V value)
   {
      key = maskNull(key);

      Entry<K, V>[] table = this.table;
      int hash = hash(key);
      int length = table.length;
      int index = index(hash, length);

      for (int start = index; ;)
      {
         Entry<K, V> e = table[index];
         if (e == null)
            break;

         if (e.hash == hash && eq(key, e.key))
         {
            table[index] = new Entry<K, V>(e.key, e.hash, value);
            return e.value;
         }

         index = nextIndex(index, length);
         if (index == start)
            throw new IllegalStateException("Table is full!");
      }

      modCount++;
      table[index] = new Entry<K, V>(key, hash, value);
      if (++size >= threshold)
         resize(length);

      return null;
   }


   @SuppressWarnings("unchecked")
   private void resize(int from)
   {
      int newLength = from << 1;

      // Can't get any bigger
      if (newLength > MAXIMUM_CAPACITY || newLength <= from)
         return;

      Entry<K, V>[] newTable = new Entry[newLength];
      Entry<K, V>[] old = table;

      for (Entry<K, V> e : old)
      {
         if (e == null)
            continue;

         int index = index(e.hash, newLength);
         while (newTable[index] != null)
            index = nextIndex(index, newLength);

         newTable[index] = e;
      }

      threshold = (int) (loadFactor * newLength);
      table = newTable;
   }

   public void putAll(Map<? extends K, ? extends V> map)
   {
      int size = map.size();
      if (size == 0)
         return;

      if (size > threshold)
      {
         if (size > MAXIMUM_CAPACITY)
            size = MAXIMUM_CAPACITY;

         int length = table.length;
         for (; length < size; length <<= 1) ;

         resize(length);
      }

      for (Map.Entry<? extends K, ? extends V> e : map.entrySet())
         put(e.getKey(), e.getValue());
   }

   public V remove(Object key)
   {
      key = maskNull(key);

      Entry<K, V>[] table = this.table;
      int length = table.length;
      int hash = hash(key);
      int start = index(hash, length);

      for (int index = start; ;)
      {
         Entry<K, V> e = table[index];
         if (e == null)
            return null;

         if (e.hash == hash && eq(key, e.key))
         {
            table[index] = null;
            relocate(index);
            modCount++;
            size--;
            return e.value;
         }

         index = nextIndex(index, length);
         if (index == start)
            return null;
      }


   }

   private void relocate(int start)
   {
      Entry<K, V>[] table = this.table;
      int length = table.length;
      int current = nextIndex(start, length);

      for (; ;)
      {
         Entry<K, V> e = table[current];
         if (e == null)
            return;

         // A Doug Lea variant of Knuth's Section 6.4 Algorithm R.
         // This provides a non-recursive method of relocating
         // entries to their optimal positions once a gap is created.
         int prefer = index(e.hash, length);
         if ((current < prefer && (prefer <= start || start <= current))
               || (prefer <= start && start <= current))
         {
            table[start] = e;
            table[current] = null;
            start = current;
         }

         current = nextIndex(current, length);
      }
   }

   public void clear()
   {
      modCount++;
      Entry<K, V>[] table = this.table;
      for (int i = 0; i < table.length; i++)
         table[i] = null;

      size = 0;
   }

   @SuppressWarnings("unchecked")
   public Object clone()
   {
      try
      {
         FastCopyHashMap<K, V> clone = (FastCopyHashMap<K, V>) super.clone();
         clone.table = table.clone();
         clone.entrySet = null;
         clone.values = null;
         clone.keySet = null;
         return clone;
      }
      catch (CloneNotSupportedException e)
      {
         // should never happen
         throw new IllegalStateException(e);
      }
   }

   public void printDebugStats()
   {
      int optimal = 0;
      int total = 0;
      int totalSkew = 0;
      int maxSkew = 0;
      for (int i = 0; i < table.length; i++)
      {
         Entry<K, V> e = table[i];
         if (e != null)
         {

            total++;
            int target = index(e.hash, table.length);
            if (i == target)
               optimal++;
            else
            {
               int skew = Math.abs(i - target);
               if (skew > maxSkew) maxSkew = skew;
               totalSkew += skew;
            }

         }
      }

      System.out.println(" Size:            " + size);
      System.out.println(" Real Size:       " + total);
      System.out.println(" Optimal:         " + optimal + " (" + (float) optimal * 100 / total + "%)");
      System.out.println(" Average Distnce: " + ((float) totalSkew / (total - optimal)));
      System.out.println(" Max Distance:    " + maxSkew);
   }

   public Set<Map.Entry<K, V>> entrySet()
   {
      if (entrySet == null)
         entrySet = new EntrySet();

      return entrySet;
   }

   public Set<K> keySet()
   {
      if (keySet == null)
         keySet = new KeySet();

      return keySet;
   }

   public Collection<V> values()
   {
      if (values == null)
         values = new Values();

      return values;
   }

   @SuppressWarnings("unchecked")
   private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException
   {
      s.defaultReadObject();

      int size = s.readInt();

      init(size, loadFactor);

      for (int i = 0; i < size; i++)
      {
         K key = (K) s.readObject();
         V value = (V) s.readObject();
         putForCreate(key, value);
      }

      this.size = size;
   }

   @SuppressWarnings("unchecked")
   private void putForCreate(K key, V value)
   {
      key = maskNull(key);

      Entry<K, V>[] table = this.table;
      int hash = hash(key);
      int length = table.length;
      int index = index(hash, length);

      Entry<K, V> e = table[index];
      while (e != null)
      {
         index = nextIndex(index, length);
         e = table[index];
      }

      table[index] = new Entry<K, V>(key, hash, value);
   }

   private void writeObject(java.io.ObjectOutputStream s) throws IOException
   {
      s.defaultWriteObject();
      s.writeInt(size);

      for (Entry<K, V> e : table)
      {
         if (e != null)
         {
            s.writeObject(unmaskNull(e.key));
            s.writeObject(e.value);
         }
      }
   }

   private static final class Entry<K, V>
   {
      final K key;
      final int hash;
      final V value;

      Entry(K key, int hash, V value)
      {
         this.key = key;
         this.hash = hash;
         this.value = value;
      }
   }

   private abstract class FasyCopyHashMapIterator<E> implements Iterator<E>
   {
      private int next = 0;
      private int expectedCount = modCount;
      private int current = -1;
      private boolean hasNext;
      Entry<K, V> table[] = FastCopyHashMap.this.table;

      public boolean hasNext()
      {
         if (hasNext == true)
            return true;

         Entry<K, V> table[] = this.table;
         for (int i = next; i < table.length; i++)
         {
            if (table[i] != null)
            {
               next = i;
               return hasNext = true;
            }
         }

         next = table.length;
         return false;
      }

      protected Entry<K, V> nextEntry()
      {
         if (modCount != expectedCount)
            throw new ConcurrentModificationException();

         if (!hasNext && !hasNext())
            throw new NoSuchElementException();

         current = next++;
         hasNext = false;

         return table[current];
      }

      @SuppressWarnings("unchecked")
      public void remove()
      {
         if (modCount != expectedCount)
            throw new ConcurrentModificationException();

         int current = this.current;
         int delete = current;

         if (current == -1)
            throw new IllegalStateException();

         // Invalidate current (prevents multiple remove)
         this.current = -1;

         // Start were we relocate
         next = delete;

         Entry<K, V>[] table = this.table;
         if (table != FastCopyHashMap.this.table)
         {
            FastCopyHashMap.this.remove(table[delete].key);
            table[delete] = null;
            expectedCount = modCount;
            return;
         }


         int length = table.length;
         int i = delete;

         table[delete] = null;
         size--;

         for (; ;)
         {
            i = nextIndex(i, length);
            Entry<K, V> e = table[i];
            if (e == null)
               break;

            int prefer = index(e.hash, length);
            if ((i < prefer && (prefer <= delete || delete <= i))
                  || (prefer <= delete && delete <= i))
            {
               // Snapshot the unseen portion of the table if we have
               // to relocate an entry that was already seen by this iterator
               if (i < current && current <= delete && table == FastCopyHashMap.this.table)
               {
                  int remaining = length - current;
                  Entry<K, V>[] newTable = (Entry<K, V>[]) new Entry[remaining];
                  System.arraycopy(table, current, newTable, 0, remaining);

                  // Replace iterator's table.
                  // Leave table local var pointing to the real table
                  this.table = newTable;
                  next = 0;
               }

               // Do the swap on the real table
               table[delete] = e;
               table[i] = null;
               delete = i;
            }
         }
      }
   }


   private class KeyIterator extends FasyCopyHashMapIterator<K>
   {
      public K next()
      {
         return unmaskNull(nextEntry().key);
      }
   }

   private class ValueIterator extends FasyCopyHashMapIterator<V>
   {
      public V next()
      {
         return nextEntry().value;
      }
   }

   private class EntryIterator extends FasyCopyHashMapIterator<Map.Entry<K, V>>
   {
      private class WriteThroughEntry extends SimpleEntry<K, V>
      {
         WriteThroughEntry(K key, V value)
         {
            super(key, value);
         }

         public V setValue(V value)
         {
            if (table != FastCopyHashMap.this.table)
               FastCopyHashMap.this.put(getKey(), value);

            return super.setValue(value);
         }
      }

      public Map.Entry<K, V> next()
      {
         Entry<K, V> e = nextEntry();
         return new WriteThroughEntry(unmaskNull(e.key), e.value);
      }

   }

   private class KeySet extends AbstractSet<K>
   {
      public Iterator<K> iterator()
      {
         return new KeyIterator();
      }

      public void clear()
      {
         FastCopyHashMap.this.clear();
      }

      public boolean contains(Object o)
      {
         return containsKey(o);
      }

      public boolean remove(Object o)
      {
         int size = size();
         FastCopyHashMap.this.remove(o);
         return size() < size;
      }

      public int size()
      {
         return FastCopyHashMap.this.size();
      }
   }

   private class Values extends AbstractCollection<V>
   {
      public Iterator<V> iterator()
      {
         return new ValueIterator();
      }

      public void clear()
      {
         FastCopyHashMap.this.clear();
      }

      public int size()
      {
         return FastCopyHashMap.this.size();
      }
   }

   private class EntrySet extends AbstractSet<Map.Entry<K, V>>
   {
      public Iterator<Map.Entry<K, V>> iterator()
      {
         return new EntryIterator();
      }

      public boolean contains(Object o)
      {
         if (!(o instanceof Map.Entry))
            return false;

         Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
         Object value = get(entry.getKey());
         return eq(entry.getValue(), value);
      }

      public void clear()
      {
         FastCopyHashMap.this.clear();
      }

      public boolean isEmpty()
      {
         return FastCopyHashMap.this.isEmpty();
      }

      public int size()
      {
         return FastCopyHashMap.this.size();
      }
   }

   protected static class SimpleEntry<K, V> implements Map.Entry<K, V>
   {
      private K key;
      private V value;

      SimpleEntry(K key, V value)
      {
         this.key = key;
         this.value = value;
      }

      SimpleEntry(Map.Entry<K, V> entry)
      {
         this.key = entry.getKey();
         this.value = entry.getValue();
      }

      public K getKey()
      {
         return key;
      }

      public V getValue()
      {
         return value;
      }

      public V setValue(V value)
      {
         V old = this.value;
         this.value = value;
         return old;
      }

      public boolean equals(Object o)
      {
         if (this == o)
            return true;

         if (!(o instanceof Map.Entry))
            return false;
         Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
         return eq(key, e.getKey()) && eq(value, e.getValue());
      }

      public int hashCode()
      {
         return (key == null ? 0 : hash(key)) ^
                (value == null ? 0 : hash(value));
      }

      public String toString()
      {
         return getKey() + "=" + getValue();
      }
   }
}
