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/*
 * Copyright (c) 2024 Contributors to the Eclipse Foundation
 *
 * 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.
 *
 *  SPDX-License-Identifier: Apache-2.0
 */
package jakarta.data.page.impl;

import jakarta.data.page.Page;
import jakarta.data.page.PageRequest;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * Record type implementing {@link Page}.
 * This may be used to simplify implementation of a repository interface.
 *
 * @param pageRequest The {@link PageRequest page request} for which this
 *                    page was obtained
 * @param content The page content
 * @param totalElements The total number of elements across all pages that
 *                      can be requested for the query. A negative value
 *                      indicates that a total count of elements and pages
 *                      is not available.
 * @param moreResults whether there is a (nonempty) next page of results
 * @param  The type of elements on the page
 */
public record PageRecord(PageRequest pageRequest, List content, long totalElements, boolean moreResults)
        implements Page {

    /**
     * Constructs a new instance, computing the {@link #moreResults}
     * component as {@code true} if the page {@code content} is a full
     * page of results and the {@code totalElements} is either unavailable
     * (indicated by a negative value) or it exceeds the current
     * {@linkplain PageRequest#page() page number} multiplied by the
     * {@link PageRequest#size() size} of a full page.
     *
     * @param pageRequest   The {@link PageRequest page request} for which
     *                      this page was obtained.
     * @param content       The page content.
     * @param totalElements The total number of elements across all pages
     *                      that can be requested for the query. A negative
     *                      value indicates that a total count of elements
     *                      and pages is not available.
     */
    public PageRecord(PageRequest pageRequest, List content, long totalElements) {
        this( pageRequest, content, totalElements,
                content.size() == pageRequest.size()
                        && (totalElements < 0
                                || totalElements > pageRequest.size() * pageRequest.page() ));
    }

    @Override
    public boolean hasContent() {
        return !content.isEmpty();
    }

    @Override
    public int numberOfElements() {
        return content.size();
    }

    @Override
    public boolean hasNext() {
        return moreResults;
    }

    @Override
    public PageRequest nextPageRequest() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

        return PageRequest.ofPage(pageRequest.page() + 1,
                                  pageRequest.size(),
                                  pageRequest.requestTotal());
    }

    @Override
    public boolean hasPrevious() {
        return pageRequest.page() > 1;
    }

    @Override
    public PageRequest previousPageRequest() {
        if (!hasPrevious()) {
            throw new NoSuchElementException();
        }

        return PageRequest.ofPage(pageRequest.page() - 1,
                pageRequest.size(),
                pageRequest.requestTotal());
    }

    @Override
    public Iterator iterator() {
        return content.iterator();
    }

    @Override
    public boolean hasTotals() {
        return totalElements >= 0;
    }

    @Override
    public long totalElements() {
        if (totalElements<0) {
            throw new IllegalStateException("total elements are not available");
        }
        return totalElements;
    }

    @Override
    public long totalPages() {
        if (totalElements<0) {
            throw new IllegalStateException("total elements are not available");
        }
        int size = pageRequest.size();
        return (totalElements + size - 1) / size;
    }
}