/**
    * Copyright 2008 Atlassian Pty Ltd 
    * 
    * 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 com.atlassian.util.concurrent;
  
  import static com.atlassian.util.concurrent.Assertions.notNull;
  import net.jcip.annotations.GuardedBy;
  import net.jcip.annotations.ThreadSafe;
  
  import java.io.Serializable;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantLock;
  
  /**
   * Abstract base class for COW {@link Map} implementations that delegate to an
   * internal map.
   * 
   * @param <K> The key type
   * @param <V> The value type
   * @param <M> the internal {@link Map} or extension for things like sorted and
   * navigable maps.
   */
  @ThreadSafe
  abstract class AbstractCopyOnWriteMap<K, V, M extends Map<K, V>> implements ConcurrentMap<K, V>, Serializable {
      private static final long serialVersionUID = 4508989182041753878L;
  
      @GuardedBy("lock")
      private volatile M delegate;
      private final transient EntrySet entrySet = new EntrySet();
      private final transient KeySet keySet = new KeySet();
      private final transient Values values = new Values();
  
      // import edu.umd.cs.findbugs.annotations.@SuppressWarnings
      private final transient Lock lock = new ReentrantLock();
  
      /**
       * Create a new {@link CopyOnWriteMap} with the supplied {@link Map} to
       * initialize the values and the {@link CopyFunction} for creating our
       * actual delegate instances.
       * 
       * @param map the initial map to initialize with
       * @param factory the copy function
       */
      protected <N extends Map<? extends K, ? extends V>> AbstractCopyOnWriteMap(final N map) {
          this.delegate = notNull("delegate", copy(notNull("map", map)));
      }
  
      /**
       * Copy function, implemented by sub-classes.
       * 
       * @param <N> the map to copy and return.
       * @param map the initial values of the newly created map.
       * @return a new map. Will never be modified after construction.
       */
      @GuardedBy("lock")
      abstract <N extends Map<? extends K, ? extends V>> M copy(N map);
  
      //
      // mutable operations
      //
  
      public final void clear() {
          lock.lock();
          try {
              final M map = copy();
              map.clear();
              set(map);
          } finally {
              lock.unlock();
          }
      }
  
      public final V remove(final Object key) {
          lock.lock();
          try {
              // short circuit if key doesn't exist
              if (!delegate.containsKey(key)) {
                  return null;
              }
              final M map = copy();
              final V result = map.remove(key);
             set(map);
             return result;
         } finally {
             lock.unlock();
         }
     }
 
     public boolean remove(final Object key, final Object value) {
         lock.lock();
         try {
             if (delegate.containsKey(key) && equals(value, delegate.get(key))) {
                 final M map = copy();
                 map.remove(key);
                 set(map);
                 return true;
             } else {
                 return false;
             }
         } finally {
             lock.unlock();
         }
     }
 
     public boolean replace(final K key, final V oldValue, final V newValue) {
         lock.lock();
         try {
             if (delegate.containsKey(key) && equals(oldValue, delegate.get(key))) {
                 final M map = copy();
                 map.put(key, newValue);
                 set(map);
                 return true;
             } else {
                 return false;
             }
         } finally {
             lock.unlock();
         }
     };
 
     public V replace(final K key, final V value) {
         lock.lock();
         try {
             if (delegate.containsKey(key)) {
                 final M map = copy();
                 try {
                     return map.put(key, value);
                 } finally {
                     set(map);
                 }
             } else {
                 return null;
             }
         } finally {
             lock.unlock();
         }
     };
 
     public final V put(final K key, final V value) {
         lock.lock();
         try {
             final M map = copy();
             final V result = map.put(key, value);
             set(map);
             return result;
         } finally {
             lock.unlock();
         }
     }
 
     public V putIfAbsent(final K key, final V value) {
         lock.lock();
         try {
             if (!delegate.containsKey(key)) {
                 final M map = copy();
                 final V result = map.put(key, value);
                 set(map);
                 return result;
             }
             return delegate.get(key);
         } finally {
             lock.unlock();
         }
     };
 
     public final void putAll(final Map<? extends K, ? extends V> t) {
         lock.lock();
         try {
             final M map = copy();
             map.putAll(t);
             set(map);
         } finally {
             lock.unlock();
         }
     }
 
     protected M copy() {
         lock.lock();
         try {
             return copy(delegate);
         } finally {
             lock.unlock();
         }
     }
 
     @GuardedBy("lock")
     protected void set(final M map) {
         delegate = map;
     }
 
     //
     // Collection views
     //
 
     public final Set<Map.Entry<K, V>> entrySet() {
         return entrySet;
     }
 
     public final Set<K> keySet() {
         return keySet;
     }
 
     public final Collection<V> values() {
         return values;
     }
 
     //
     // delegate operations
     //
 
     public final boolean containsKey(final Object key) {
         return delegate.containsKey(key);
     }
 
     public final boolean containsValue(final Object value) {
         return delegate.containsValue(value);
     }
 
     public final V get(final Object key) {
         return delegate.get(key);
     }
 
     public final boolean isEmpty() {
         return delegate.isEmpty();
     }
 
     public final int size() {
         return delegate.size();
     }
 
     @Override
     public final boolean equals(final Object o) {
         return delegate.equals(o);
     }
 
     @Override
     public final int hashCode() {
         return delegate.hashCode();
     }
 
     protected final M getDelegate() {
         return delegate;
     }
 
     @Override
     public String toString() {
         return delegate.toString();
     }
 
     //
     // inner classes
     //
 
     private class KeySet extends CollectionView<K> implements Set<K> {
 
         @Override
         Collection<K> getDelegate() {
             return delegate.keySet();
         }
 
         //
         // mutable operations
         //
 
         public void clear() {
             lock.lock();
             try {
                 final M map = copy();
                 map.keySet().clear();
                 set(map);
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean remove(final Object o) {
             return AbstractCopyOnWriteMap.this.remove(o) != null;
         }
 
         public boolean removeAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.keySet().removeAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean retainAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.keySet().retainAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
     }
 
     private final class Values extends CollectionView<V> {
 
         @Override
         Collection<V> getDelegate() {
             return delegate.values();
         }
 
         public void clear() {
             lock.lock();
             try {
                 final M map = copy();
                 map.values().clear();
                 set(map);
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean remove(final Object o) {
             lock.lock();
             try {
                 if (!contains(o)) {
                     return false;
                 }
                 final M map = copy();
                 final boolean result = map.values().remove(o);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean removeAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.values().removeAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean retainAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.values().retainAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
     }
 
     private class EntrySet extends CollectionView<Entry<K, V>> implements Set<Map.Entry<K, V>> {
 
         @Override
         Collection<java.util.Map.Entry<K, V>> getDelegate() {
             return delegate.entrySet();
         }
 
         public void clear() {
             lock.lock();
             try {
                 final M map = copy();
                 map.entrySet().clear();
                 set(map);
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean remove(final Object o) {
             lock.lock();
             try {
                 if (!contains(o)) {
                     return false;
                 }
                 final M map = copy();
                 final boolean result = map.entrySet().remove(o);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean removeAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.entrySet().removeAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
 
         public boolean retainAll(final Collection<?> c) {
             lock.lock();
             try {
                 final M map = copy();
                 final boolean result = map.entrySet().retainAll(c);
                 set(map);
                 return result;
             } finally {
                 lock.unlock();
             }
         }
     }
 
     private static class UnmodifiableIterator<T> implements Iterator<T> {
         private final Iterator<T> delegate;
 
         public UnmodifiableIterator(final Iterator<T> delegate) {
             this.delegate = delegate;
         }
 
         public boolean hasNext() {
             return delegate.hasNext();
         }
 
         public T next() {
             return delegate.next();
         }
 
         public void remove() {
             throw new UnsupportedOperationException();
         }
     }
 
     protected static abstract class CollectionView<E> implements Collection<E> {
 
         abstract Collection<E> getDelegate();
 
         //
         // delegate operations
         //
 
         public final boolean contains(final Object o) {
             return getDelegate().contains(o);
         }
 
         public final boolean containsAll(final Collection<?> c) {
             return getDelegate().containsAll(c);
         }
 
         public final Iterator<E> iterator() {
             return new UnmodifiableIterator<E>(getDelegate().iterator());
         }
 
         public final boolean isEmpty() {
             return getDelegate().isEmpty();
         }
 
         public final int size() {
             return getDelegate().size();
         }
 
         public final Object[] toArray() {
             return getDelegate().toArray();
         }
 
         public final <T> T[] toArray(final T[] a) {
             return getDelegate().toArray(a);
         }
 
         @Override
         public int hashCode() {
             return getDelegate().hashCode();
         }
 
         @Override
         public boolean equals(final Object obj) {
             return getDelegate().equals(obj);
         }
 
         @Override
         public String toString() {
             return getDelegate().toString();
         }
 
         //
         // unsupported operations
         //
 
         public final boolean add(final E o) {
             throw new UnsupportedOperationException();
         }
 
         public final boolean addAll(final Collection<? extends E> c) {
             throw new UnsupportedOperationException();
         }
     }
 
     private boolean equals(final Object o1, final Object o2) {
         if (o1 == null) {
             return o2 == null;
         }
         return o1.equals(o2);
     }
 }