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MyBatis framework for generating dynamic SQL
There is a newer version: 1.5.2
/**
 *    Copyright 2016-2019 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.mybatis.dynamic.sql.select.render;

import java.util.Optional;
import java.util.concurrent.atomic.AtomicInteger;

import org.mybatis.dynamic.sql.render.RenderingStrategy;
import org.mybatis.dynamic.sql.select.PagingModel;
import org.mybatis.dynamic.sql.util.FragmentAndParameters;

public class FetchFirstPagingModelRenderer {
    private RenderingStrategy renderingStrategy;
    private PagingModel pagingModel;
    private AtomicInteger sequence;

    public FetchFirstPagingModelRenderer(RenderingStrategy renderingStrategy,
            PagingModel pagingModel, AtomicInteger sequence) {
        this.renderingStrategy = renderingStrategy;
        this.pagingModel = pagingModel;
        this.sequence = sequence;
    }

    public Optional render() {
        return pagingModel.offset()
                .map(this::renderWithOffset)
                .orElseGet(this::renderFetchFirstRowsOnly);
    }

    private Optional renderWithOffset(Long offset) {
        return pagingModel.fetchFirstRows()
                .map(ffr -> renderOffsetAndFetchFirstRows(offset, ffr))
                .orElseGet(() -> renderOffsetOnly(offset));
    }

    private Optional renderFetchFirstRowsOnly() {
        return pagingModel.fetchFirstRows().flatMap(this::renderFetchFirstRowsOnly);
    }

    private Optional renderFetchFirstRowsOnly(Long fetchFirstRows) {
        String mapKey = RenderingStrategy.formatParameterMapKey(sequence);
        return FragmentAndParameters
                .withFragment("fetch first " + renderPlaceholder(mapKey) //$NON-NLS-1$
                    + " rows only") //$NON-NLS-1$
                .withParameter(mapKey, fetchFirstRows)
                .buildOptional();
    }

    private Optional renderOffsetOnly(Long offset) {
        String mapKey = RenderingStrategy.formatParameterMapKey(sequence);
        return FragmentAndParameters.withFragment("offset " + renderPlaceholder(mapKey) //$NON-NLS-1$
                + " rows") //$NON-NLS-1$
                .withParameter(mapKey, offset)
                .buildOptional();
    }

    private Optional renderOffsetAndFetchFirstRows(Long offset, Long fetchFirstRows) {
        String mapKey1 = RenderingStrategy.formatParameterMapKey(sequence);
        String mapKey2 = RenderingStrategy.formatParameterMapKey(sequence);
        return FragmentAndParameters.withFragment("offset " + renderPlaceholder(mapKey1) //$NON-NLS-1$
                + " rows fetch first " + renderPlaceholder(mapKey2) //$NON-NLS-1$
                + " rows only") //$NON-NLS-1$
                .withParameter(mapKey1, offset)
                .withParameter(mapKey2, fetchFirstRows)
                .buildOptional();
    }

    private String renderPlaceholder(String parameterName) {
        return renderingStrategy.getFormattedJdbcPlaceholder(RenderingStrategy.DEFAULT_PARAMETER_PREFIX,
                parameterName);
    }
}