/*
 * Copyright 2008-2020 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
 *
 *      https://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.data.domain;

import java.util.List;
import java.util.function.Function;

import org.springframework.lang.Nullable;

Basic Page implementation. 
Author:
Oliver Gierke, Mark Paluch
Type parameters:
<T> – the type of which the page consists./**
 * Basic {@code Page} implementation.
 *
 * @param <T> the type of which the page consists.
 * @author Oliver Gierke
 * @author Mark Paluch
 */
public class PageImpl<T> extends Chunk<T> implements Page<T> {

	private static final long serialVersionUID = 867755909294344406L;

	private final long total;

	
Constructor of PageImpl. 
Params:
content – the content of this page, must not be null.
pageable – the paging information, must not be null.
total – the total amount of items available. The total might be adapted considering the length of the content
         given, if it is going to be the content of the last page. This is in place to mitigate inconsistencies./**
	 * Constructor of {@code PageImpl}.
	 *
	 * @param content the content of this page, must not be {@literal null}.
	 * @param pageable the paging information, must not be {@literal null}.
	 * @param total the total amount of items available. The total might be adapted considering the length of the content
	 *          given, if it is going to be the content of the last page. This is in place to mitigate inconsistencies.
	 */
	public PageImpl(List<T> content, Pageable pageable, long total) {

		super(content, pageable);

		this.total = pageable.toOptional().filter(it -> !content.isEmpty())//
				.filter(it -> it.getOffset() + it.getPageSize() > total)//
				.map(it -> it.getOffset() + content.size())//
				.orElse(total);
	}

	
Creates a new PageImpl with the given content. This will result in the created Page being identical to the entire List. 
Params:
content – must not be null./**
	 * Creates a new {@link PageImpl} with the given content. This will result in the created {@link Page} being identical
	 * to the entire {@link List}.
	 *
	 * @param content must not be {@literal null}.
	 */
	public PageImpl(List<T> content) {
		this(content, Pageable.unpaged(), null == content ? 0 : content.size());
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.domain.Page#getTotalPages()
	 */
	@Override
	public int getTotalPages() {
		return getSize() == 0 ? 1 : (int) Math.ceil((double) total / (double) getSize());
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.domain.Page#getTotalElements()
	 */
	@Override
	public long getTotalElements() {
		return total;
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.domain.Slice#hasNext()
	 */
	@Override
	public boolean hasNext() {
		return getNumber() + 1 < getTotalPages();
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.domain.Slice#isLast()
	 */
	@Override
	public boolean isLast() {
		return !hasNext();
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.domain.Slice#transform(org.springframework.core.convert.converter.Converter)
	 */
	@Override
	public <U> Page<U> map(Function<? super T, ? extends U> converter) {
		return new PageImpl<>(getConvertedContent(converter), getPageable(), total);
	}

	/*
	 * (non-Javadoc)
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {

		String contentType = "UNKNOWN";
		List<T> content = getContent();

		if (content.size() > 0) {
			contentType = content.get(0).getClass().getName();
		}

		return String.format("Page %s of %d containing %s instances", getNumber() + 1, getTotalPages(), contentType);
	}

	/*
	 * (non-Javadoc)
	 * @see java.lang.Object#equals(java.lang.Object)
	 */
	@Override
	public boolean equals(@Nullable Object obj) {

		if (this == obj) {
			return true;
		}

		if (!(obj instanceof PageImpl<?>)) {
			return false;
		}

		PageImpl<?> that = (PageImpl<?>) obj;

		return this.total == that.total && super.equals(obj);
	}

	/*
	 * (non-Javadoc)
	 * @see java.lang.Object#hashCode()
	 */
	@Override
	public int hashCode() {

		int result = 17;

		result += 31 * (int) (total ^ total >>> 32);
		result += 31 * super.hashCode();

		return result;
	}
}