/*
 * Hibernate Validator, declare and validate application constraints
 *
 * License: Apache License, Version 2.0
 * See the license.txt file in the root directory or <http://www.apache.org/licenses/LICENSE-2.0>.
 */
package org.hibernate.validator.internal.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

Provides some methods for simplified collection instantiation.
Author:
Gunnar Morling, Kevin Pollet <kevin.pollet@serli.com> (C) 2011 SERLI, Hardy Ferentschik, Guillaume Smet/**
 * Provides some methods for simplified collection instantiation.
 *
 * @author Gunnar Morling
 * @author Kevin Pollet &lt;kevin.pollet@serli.com&gt; (C) 2011 SERLI
 * @author Hardy Ferentschik
 * @author Guillaume Smet
 */
public final class CollectionHelper {

	private CollectionHelper() {
	}

	public static <K, V> HashMap<K, V> newHashMap() {
		return new HashMap<K, V>();
	}

	public static <K, V> HashMap<K, V> newHashMap(int size) {
		return new HashMap<K, V>( getInitialCapacityFromExpectedSize( size ) );
	}

	public static <K, V> HashMap<K, V> newHashMap(Map<K, V> map) {
		return new HashMap<K, V>( map );
	}

	public static <K, V> ConcurrentHashMap<K, V> newConcurrentHashMap() {
		return new ConcurrentHashMap<K, V>();
	}

	public static <T> HashSet<T> newHashSet() {
		return new HashSet<T>();
	}

	public static <T> HashSet<T> newHashSet(int size) {
		return new HashSet<T>( getInitialCapacityFromExpectedSize( size ) );
	}

	public static <T> HashSet<T> newHashSet(Collection<? extends T> c) {
		return new HashSet<T>( c );
	}

	public static <T> HashSet<T> newHashSet(Iterable<? extends T> iterable) {
		HashSet<T> set = newHashSet();
		for ( T t : iterable ) {
			set.add( t );
		}
		return set;
	}

	public static <T> ArrayList<T> newArrayList() {
		return new ArrayList<T>();
	}

	public static <T> ArrayList<T> newArrayList(int size) {
		return new ArrayList<T>( size );
	}

	@SafeVarargs
	public static <T> ArrayList<T> newArrayList(Iterable<T>... iterables) {
		ArrayList<T> resultList = newArrayList();
		for ( Iterable<T> oneIterable : iterables ) {
			for ( T oneElement : oneIterable ) {
				resultList.add( oneElement );
			}
		}
		return resultList;
	}

	@SafeVarargs
	public static <T> Set<T> asSet(T... ts) {
		return new HashSet<>( Arrays.asList( ts ) );
	}

	public static <T> List<T> toImmutableList(List<? extends T> list) {
		switch ( list.size() ) {
			case 0:
				return Collections.emptyList();
			case 1:
				return Collections.singletonList( list.get( 0 ) );
			default:
				return Collections.unmodifiableList( list );
		}
	}

	public static <T> Set<T> toImmutableSet(Set<? extends T> set) {
		switch ( set.size() ) {
			case 0:
				return Collections.emptySet();
			case 1:
				return Collections.singleton( set.iterator().next() );
			default:
				return Collections.unmodifiableSet( set );
		}
	}

	public static <K, V> Map<K, V> toImmutableMap(Map<K, V> map) {
		switch ( map.size() ) {
			case 0:
				return Collections.emptyMap();
			case 1:
				Entry<K, V> entry = map.entrySet().iterator().next();
				return Collections.singletonMap( entry.getKey(), entry.getValue() );
			default:
				return Collections.unmodifiableMap( map );
		}
	}

	
As the default loadFactor is of 0.75, we need to calculate the initial capacity from the expected size to avoid resizing the collection when we populate the collection with all the initial elements. We use a calculation similar to what is done in HashMap.putAll(Map). 
Params:
expectedSize – the expected size of the collection
Returns:
the initial capacity of the collection/**
	 * As the default loadFactor is of 0.75, we need to calculate the initial capacity from the expected size to avoid
	 * resizing the collection when we populate the collection with all the initial elements. We use a calculation
	 * similar to what is done in {@link HashMap#putAll(Map)}.
	 *
	 * @param expectedSize the expected size of the collection
	 * @return the initial capacity of the collection
	 */
	private static int getInitialCapacityFromExpectedSize(int expectedSize) {
		if ( expectedSize < 3 ) {
			return expectedSize + 1;
		}
		return (int) ( (float) expectedSize / 0.75f + 1.0f );
	}

	
Builds an Iterator for a given array. It is (un)necessarily ugly because we have to deal with array of primitives. 
Params:
object – a given array
Returns:
an Iterator iterating over the array/**
	 * Builds an {@link Iterator} for a given array. It is (un)necessarily ugly because we have to deal with array of primitives.
	 *
	 * @param object a given array
	 * @return an {@code Iterator} iterating over the array
	 */
	@SuppressWarnings({ "unchecked", "rawtypes" }) // Reflection is used to ensure the correct types are used
	public static Iterator<?> iteratorFromArray(Object object) {
		return new ArrayIterator( accessorFromArray( object ), object );
	}

	
Builds an Iterable for a given array. It is (un)necessarily ugly because we have to deal with array of primitives. 
Params:
object – a given array
Returns:
an Iterable providing iterators over the array/**
	 * Builds an {@link Iterable} for a given array. It is (un)necessarily ugly because we have to deal with array of primitives.
	 *
	 * @param object a given array
	 * @return an {@code Iterable} providing iterators over the array
	 */
	@SuppressWarnings({ "unchecked", "rawtypes" }) // Reflection is used to ensure the correct types are used
	public static Iterable<?> iterableFromArray(Object object) {
		return new ArrayIterable( accessorFromArray( object ), object );
	}

	private static ArrayAccessor<?, ?> accessorFromArray(Object object) {
		ArrayAccessor<?, ?> accessor;
		if ( Object.class.isAssignableFrom( object.getClass().getComponentType() ) ) {
			accessor = ArrayAccessor.OBJECT;
		}
		else if ( object.getClass() == boolean[].class ) {
			accessor = ArrayAccessor.BOOLEAN;
		}
		else if ( object.getClass() == int[].class ) {
			accessor = ArrayAccessor.INT;
		}
		else if ( object.getClass() == long[].class ) {
			accessor = ArrayAccessor.LONG;
		}
		else if ( object.getClass() == double[].class ) {
			accessor = ArrayAccessor.DOUBLE;
		}
		else if ( object.getClass() == float[].class ) {
			accessor = ArrayAccessor.FLOAT;
		}
		else if ( object.getClass() == byte[].class ) {
			accessor = ArrayAccessor.BYTE;
		}
		else if ( object.getClass() == short[].class ) {
			accessor = ArrayAccessor.SHORT;
		}
		else if ( object.getClass() == char[].class ) {
			accessor = ArrayAccessor.CHAR;
		}
		else {
			throw new IllegalArgumentException( "Provided object " + object + " is not a supported array type" );
		}
		return accessor;
	}

	private static class ArrayIterable<A, T> implements Iterable<T> {
		private final ArrayAccessor<A, T> accessor;
		private final A values;

		public ArrayIterable(ArrayAccessor<A, T> accessor, A values) {
			this.accessor = accessor;
			this.values = values;
		}

		@Override
		public final Iterator<T> iterator() {
			return new ArrayIterator<>( accessor, values );
		}
	}

	private static class ArrayIterator<A, T> implements Iterator<T> {
		private final ArrayAccessor<A, T> accessor;
		private final A values;
		private int current = 0;

		public ArrayIterator(ArrayAccessor<A, T> accessor, A values) {
			this.accessor = accessor;
			this.values = values;
		}

		@Override
		public boolean hasNext() {
			return current < accessor.size( values );
		}

		@Override
		public T next() {
			T result = accessor.get( values, current );
			current++;
			return result;
		}
	}

	private interface ArrayAccessor<A, T> {

		int size(A array);

		T get(A array, int index);

		ArrayAccessor<Object[], Object> OBJECT = new ArrayAccessor<Object[], Object>() {
			@Override
			public int size(Object[] array) {
				return array.length;
			}

			@Override
			public Object get(Object[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<boolean[], Boolean> BOOLEAN = new ArrayAccessor<boolean[], Boolean>() {
			@Override
			public int size(boolean[] array) {
				return array.length;
			}

			@Override
			public Boolean get(boolean[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<int[], Integer> INT = new ArrayAccessor<int[], Integer>() {
			@Override
			public int size(int[] array) {
				return array.length;
			}

			@Override
			public Integer get(int[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<long[], Long> LONG = new ArrayAccessor<long[], Long>() {
			@Override
			public int size(long[] array) {
				return array.length;
			}

			@Override
			public Long get(long[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<double[], Double> DOUBLE = new ArrayAccessor<double[], Double>() {
			@Override
			public int size(double[] array) {
				return array.length;
			}

			@Override
			public Double get(double[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<float[], Float> FLOAT = new ArrayAccessor<float[], Float>() {
			@Override
			public int size(float[] array) {
				return array.length;
			}

			@Override
			public Float get(float[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<byte[], Byte> BYTE = new ArrayAccessor<byte[], Byte>() {
			@Override
			public int size(byte[] array) {
				return array.length;
			}

			@Override
			public Byte get(byte[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<short[], Short> SHORT = new ArrayAccessor<short[], Short>() {
			@Override
			public int size(short[] array) {
				return array.length;
			}

			@Override
			public Short get(short[] array, int index) {
				return array[index];
			}
		};

		ArrayAccessor<char[], Character> CHAR = new ArrayAccessor<char[], Character>() {
			@Override
			public int size(char[] array) {
				return array.length;
			}

			@Override
			public Character get(char[] array, int index) {
				return array[index];
			}
		};
	}
}