/*
	* Copyright (C) 2002-2019 Sebastiano Vigna
	*
	* 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 it.unimi.dsi.fastutil.objects;
import it.unimi.dsi.fastutil.Function;
A class providing static methods and objects that do useful things with
type-specific functions.
See Also:
Function
Collections/**
 * A class providing static methods and objects that do useful things with
 * type-specific functions.
 *
 * @see it.unimi.dsi.fastutil.Function
 * @see java.util.Collections
 */
public final class Reference2ObjectFunctions {
	private Reference2ObjectFunctions() {
	}
	
An immutable class representing an empty type-specific function.

This class may be useful to implement your own in case you subclass a
type-specific function.
/**
	 * An immutable class representing an empty type-specific function.
	 *
	 * <p>
	 * This class may be useful to implement your own in case you subclass a
	 * type-specific function.
	 */
	public static class EmptyFunction<K, V> extends AbstractReference2ObjectFunction<K, V>
			implements
				java.io.Serializable,
				Cloneable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected EmptyFunction() {
		}
		@Override
		public V get(final Object k) {
			return (null);
		}
		@Override
		public boolean containsKey(final Object k) {
			return false;
		}
		@Override
		public V defaultReturnValue() {
			return (null);
		}
		@Override
		public void defaultReturnValue(final V defRetValue) {
			throw new UnsupportedOperationException();
		}
		@Override
		public int size() {
			return 0;
		}
		@Override
		public void clear() {
		}
		@Override
		public Object clone() {
			return EMPTY_FUNCTION;
		}
		@Override
		public int hashCode() {
			return 0;
		}
		@Override
		public boolean equals(final Object o) {
			if (!(o instanceof Function))
				return false;
			return ((Function<?, ?>) o).size() == 0;
		}
		@Override
		public String toString() {
			return "{}";
		}
		private Object readResolve() {
			return EMPTY_FUNCTION;
		}
	}
	
An empty type-specific function (immutable). It is serializable and
cloneable.
/**
	 * An empty type-specific function (immutable). It is serializable and
	 * cloneable.
	 */
	@SuppressWarnings("rawtypes")
	public static final EmptyFunction EMPTY_FUNCTION = new EmptyFunction();
	
An immutable class representing a type-specific singleton function. Note that
the default return value is still settable.

Note that albeit the function is immutable, its default return value may be
changed.

This class may be useful to implement your own in case you subclass a
type-specific function.
/**
	 * An immutable class representing a type-specific singleton function. Note that
	 * the default return value is still settable.
	 *
	 * <p>
	 * Note that albeit the function is immutable, its default return value may be
	 * changed.
	 *
	 * <p>
	 * This class may be useful to implement your own in case you subclass a
	 * type-specific function.
	 */
	public static class Singleton<K, V> extends AbstractReference2ObjectFunction<K, V>
			implements
				java.io.Serializable,
				Cloneable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final K key;
		protected final V value;
		protected Singleton(final K key, final V value) {
			this.key = key;
			this.value = value;
		}
		@Override
		public boolean containsKey(final Object k) {
			return ((key) == (k));
		}
		@Override
		public V get(final Object k) {
			return ((key) == (k)) ? value : defRetValue;
		}
		@Override
		public int size() {
			return 1;
		}
		@Override
		public Object clone() {
			return this;
		}
	}
	
Returns a type-specific immutable function containing only the specified
pair. The returned function is serializable and cloneable.

Note that albeit the returned function is immutable, its default return value
may be changed.
Params:
key – 
           the only key of the returned function.
value – 
           the only value of the returned function.
Returns:
a type-specific immutable function containing just the pair &lt;key,value&gt;./**
	 * Returns a type-specific immutable function containing only the specified
	 * pair. The returned function is serializable and cloneable.
	 *
	 * <p>
	 * Note that albeit the returned function is immutable, its default return value
	 * may be changed.
	 *
	 * @param key
	 *            the only key of the returned function.
	 * @param value
	 *            the only value of the returned function.
	 * @return a type-specific immutable function containing just the pair
	 *         {@code &lt;key,value&gt;}.
	 */
	public static <K, V> Reference2ObjectFunction<K, V> singleton(final K key, V value) {
		return new Singleton<>(key, value);
	}
	
A synchronized wrapper class for functions. /** A synchronized wrapper class for functions. */
	public static class SynchronizedFunction<K, V> implements Reference2ObjectFunction<K, V>, java.io.Serializable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final Reference2ObjectFunction<K, V> function;
		protected final Object sync;
		protected SynchronizedFunction(final Reference2ObjectFunction<K, V> f, final Object sync) {
			if (f == null)
				throw new NullPointerException();
			this.function = f;
			this.sync = sync;
		}
		protected SynchronizedFunction(final Reference2ObjectFunction<K, V> f) {
			if (f == null)
				throw new NullPointerException();
			this.function = f;
			this.sync = this;
		}
		@Override
		public V apply(final K key) {
			synchronized (sync) {
				return function.apply(key);
			}
		}
		@Override
		public int size() {
			synchronized (sync) {
				return function.size();
			}
		}
		@Override
		public V defaultReturnValue() {
			synchronized (sync) {
				return function.defaultReturnValue();
			}
		}
		@Override
		public void defaultReturnValue(final V defRetValue) {
			synchronized (sync) {
				function.defaultReturnValue(defRetValue);
			}
		}
		@Override
		public boolean containsKey(final Object k) {
			synchronized (sync) {
				return function.containsKey(k);
			}
		}
		@Override
		public V put(final K k, final V v) {
			synchronized (sync) {
				return function.put(k, v);
			}
		}
		@Override
		public V get(final Object k) {
			synchronized (sync) {
				return function.get(k);
			}
		}
		@Override
		public V remove(final Object k) {
			synchronized (sync) {
				return function.remove(k);
			}
		}
		@Override
		public void clear() {
			synchronized (sync) {
				function.clear();
			}
		}
		@Override
		public int hashCode() {
			synchronized (sync) {
				return function.hashCode();
			}
		}
		@Override
		public boolean equals(final Object o) {
			if (o == this)
				return true;
			synchronized (sync) {
				return function.equals(o);
			}
		}
		@Override
		public String toString() {
			synchronized (sync) {
				return function.toString();
			}
		}
		private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
			synchronized (sync) {
				s.defaultWriteObject();
			}
		}
	}
	
Returns a synchronized type-specific function backed by the given
type-specific function.
Params:
f – 
           the function to be wrapped in a synchronized function.
See Also:
Collections.synchronizedMap(Map<Object,Object>)
Returns:
a synchronized view of the specified function./**
	 * Returns a synchronized type-specific function backed by the given
	 * type-specific function.
	 *
	 * @param f
	 *            the function to be wrapped in a synchronized function.
	 * @return a synchronized view of the specified function.
	 * @see java.util.Collections#synchronizedMap(java.util.Map)
	 */
	public static <K, V> Reference2ObjectFunction<K, V> synchronize(final Reference2ObjectFunction<K, V> f) {
		return new SynchronizedFunction<>(f);
	}
	
Returns a synchronized type-specific function backed by the given
type-specific function, using an assigned object to synchronize.
Params:
f – 
           the function to be wrapped in a synchronized function.
sync – 
           an object that will be used to synchronize the access to the
           function.
See Also:
Collections.synchronizedMap(Map<Object,Object>)
Returns:
a synchronized view of the specified function./**
	 * Returns a synchronized type-specific function backed by the given
	 * type-specific function, using an assigned object to synchronize.
	 *
	 * @param f
	 *            the function to be wrapped in a synchronized function.
	 * @param sync
	 *            an object that will be used to synchronize the access to the
	 *            function.
	 * @return a synchronized view of the specified function.
	 * @see java.util.Collections#synchronizedMap(java.util.Map)
	 */
	public static <K, V> Reference2ObjectFunction<K, V> synchronize(final Reference2ObjectFunction<K, V> f,
			final Object sync) {
		return new SynchronizedFunction<>(f, sync);
	}
	
An unmodifiable wrapper class for functions. /** An unmodifiable wrapper class for functions. */
	public static class UnmodifiableFunction<K, V> extends AbstractReference2ObjectFunction<K, V>
			implements
				java.io.Serializable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final Reference2ObjectFunction<K, V> function;
		protected UnmodifiableFunction(final Reference2ObjectFunction<K, V> f) {
			if (f == null)
				throw new NullPointerException();
			this.function = f;
		}
		@Override
		public int size() {
			return function.size();
		}
		@Override
		public V defaultReturnValue() {
			return function.defaultReturnValue();
		}
		@Override
		public void defaultReturnValue(final V defRetValue) {
			throw new UnsupportedOperationException();
		}
		@Override
		public boolean containsKey(final Object k) {
			return function.containsKey(k);
		}
		@Override
		public V put(final K k, final V v) {
			throw new UnsupportedOperationException();
		}
		@Override
		public V get(final Object k) {
			return function.get(k);
		}
		@Override
		public V remove(final Object k) {
			throw new UnsupportedOperationException();
		}
		@Override
		public void clear() {
			throw new UnsupportedOperationException();
		}
		@Override
		public int hashCode() {
			return function.hashCode();
		}
		@Override
		public boolean equals(Object o) {
			return o == this || function.equals(o);
		}
		@Override
		public String toString() {
			return function.toString();
		}
	}
	
Returns an unmodifiable type-specific function backed by the given
type-specific function.
Params:
f – 
           the function to be wrapped in an unmodifiable function.
See Also:
Collections.unmodifiableMap(Map<? extends Object,? extends Object>)
Returns:
an unmodifiable view of the specified function./**
	 * Returns an unmodifiable type-specific function backed by the given
	 * type-specific function.
	 *
	 * @param f
	 *            the function to be wrapped in an unmodifiable function.
	 * @return an unmodifiable view of the specified function.
	 * @see java.util.Collections#unmodifiableMap(java.util.Map)
	 */
	public static <K, V> Reference2ObjectFunction<K, V> unmodifiable(final Reference2ObjectFunction<K, V> f) {
		return new UnmodifiableFunction<>(f);
	}
}