/*
 * Copyright 2002-2017 the original author or authors.
 *
 * 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 org.springframework.core.convert.support;

import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;

import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

Converts a Collection to an array.
First, creates a new array of the requested targetType with a length equal to the
size of the source Collection. Then sets each collection element into the array.
Will perform an element conversion from the collection's parameterized type to the
array's component type if necessary.
Author:
Keith Donald, Juergen Hoeller
Since:
3.0/**
 * Converts a Collection to an array.
 *
 * <p>First, creates a new array of the requested targetType with a length equal to the
 * size of the source Collection. Then sets each collection element into the array.
 * Will perform an element conversion from the collection's parameterized type to the
 * array's component type if necessary.
 *
 * @author Keith Donald
 * @author Juergen Hoeller
 * @since 3.0
 */
final class CollectionToArrayConverter implements ConditionalGenericConverter {

	private final ConversionService conversionService;


	public CollectionToArrayConverter(ConversionService conversionService) {
		this.conversionService = conversionService;
	}


	@Override
	public Set<ConvertiblePair> getConvertibleTypes() {
		return Collections.singleton(new ConvertiblePair(Collection.class, Object[].class));
	}

	@Override
	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
		return ConversionUtils.canConvertElements(sourceType.getElementTypeDescriptor(),
				targetType.getElementTypeDescriptor(), this.conversionService);
	}

	@Override
	@Nullable
	public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
		if (source == null) {
			return null;
		}
		Collection<?> sourceCollection = (Collection<?>) source;
		TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
		Assert.state(targetElementType != null, "No target element type");
		Object array = Array.newInstance(targetElementType.getType(), sourceCollection.size());
		int i = 0;
		for (Object sourceElement : sourceCollection) {
			Object targetElement = this.conversionService.convert(sourceElement,
					sourceType.elementTypeDescriptor(sourceElement), targetElementType);
			Array.set(array, i++, targetElement);
		}
		return array;
	}

}