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The MyBatis SQL mapper framework makes it easier to use a relational database with object-oriented applications. MyBatis couples objects with stored procedures or SQL statements using a XML descriptor or annotations. Simplicity is the biggest advantage of the MyBatis data mapper over object relational mapping tools.

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/**
 *    Copyright 2009-2017 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.apache.ibatis.features.jpa.domain;

import org.apache.ibatis.utils.Assert;

import java.util.Optional;

public interface Pageable {

	/**
	 * Returns a {@link Pageable} instance representing no pagination setup.
	 * 
	 * @return
	 */
	static Pageable unpaged() {
		return Unpaged.INSTANCE;
	}

	/**
	 * Returns whether the current {@link Pageable} contains pagination information.
	 * 
	 * @return
	 */
	default boolean isPaged() {
		return true;
	}

	/**
	 * Returns whether the current {@link Pageable} does not contain pagination information.
	 * 
	 * @return
	 */
	default boolean isUnpaged() {
		return !isPaged();
	}

	/**
	 * Returns the page to be returned.
	 * 
	 * @return the page to be returned.
	 */
	int getPageNumber();

	/**
	 * Returns the number of items to be returned.
	 * 
	 * @return the number of items of that page
	 */
	int getPageSize();

	/**
	 * Returns the offset to be taken according to the underlying page and page size.
	 * 
	 * @return the offset to be taken
	 */
	long getOffset();

	/**
	 * Returns the sorting parameters.
	 * 
	 * @return
	 */
	Sort getSort();

	/**
	 * Returns the current {@link Sort} or the given one if the current one is unsorted.
	 * 
	 * @param sort must not be {@literal null}.
	 * @return
	 */
	default Sort getSortOr(Sort sort) {

		Assert.notNull(sort, "Fallback Sort must not be null!");

		return getSort().isSorted() ? getSort() : sort;
	}

	/**
	 * Returns the {@link Pageable} requesting the next {@link Page}.
	 * 
	 * @return
	 */
	Pageable next();

	/**
	 * Returns the previous {@link Pageable} or the first {@link Pageable} if the current one already is the first one.
	 * 
	 * @return
	 */
	Pageable previousOrFirst();

	/**
	 * Returns the {@link Pageable} requesting the first page.
	 * 
	 * @return
	 */
	Pageable first();

	/**
	 * Returns whether there's a previous {@link Pageable} we can access from the current one. Will return
	 * {@literal false} in case the current {@link Pageable} already refers to the first page.
	 * 
	 * @return
	 */
	boolean hasPrevious();

	/**
	 * Returns an {@link Optional} so that it can easily be mapped on.
	 * 
	 * @return
	 */
	default Optional toOptional() {
		return isUnpaged() ? Optional.empty() : Optional.of(this);
	}
}