/*
    *    Copyright 2016-2025 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 examples.paging;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Objects;
  import java.util.function.Function;
  
  import org.mybatis.dynamic.sql.render.RenderingStrategies;
  import org.mybatis.dynamic.sql.select.SelectModel;
  import org.mybatis.dynamic.sql.select.render.SelectStatementProvider;
  
  /**
   * This adapter modifies the generated SQL by adding a LIMIT and OFFSET clause at the end
   * of the generated SQL.  This can be used to create a paginated query.
   *
   * <p>LIMIT and OFFSET has limited support in relational databases, so this cannot be considered
   * a general solution for all paginated queries (and that is why this adapter lives only in the
   * test source tree and is not packaged with the core library code).
   *
   * <p>I believe it works in MySQL, HSQLDB, and Postgres.
   *
   * <p><b>Important Note: </b> this adapter is no longer required for limit and offset support as the
   * library now supports limit and offset natively. However, this remains a good example of altering the generated
   * SQL before it is executed.
   *
   * @author Jeff Butler
   */
  public class LimitAndOffsetAdapter<R> {
      private final SelectModel selectModel;
      private final Function<SelectStatementProvider, R> mapperMethod;
      private final int limit;
      private final int offset;
  
      private LimitAndOffsetAdapter(SelectModel selectModel, Function<SelectStatementProvider, R> mapperMethod,
              int limit, int offset) {
          this.selectModel = Objects.requireNonNull(selectModel);
          this.mapperMethod = Objects.requireNonNull(mapperMethod);
          this.limit = limit;
          this.offset = offset;
      }
  
      public R execute() {
          return mapperMethod.apply(selectStatement());
      }
  
      private SelectStatementProvider selectStatement() {
          return new LimitAndOffsetDecorator(
                  selectModel.render(RenderingStrategies.MYBATIS3));
      }
  
      public static <R> LimitAndOffsetAdapter<R> of(SelectModel selectModel,
              Function<SelectStatementProvider, R> mapperMethod, int limit, int offset) {
          return new LimitAndOffsetAdapter<>(selectModel, mapperMethod, limit, offset);
      }
  
      public class LimitAndOffsetDecorator implements SelectStatementProvider {
          private final Map<String, Object> parameters = new HashMap<>();
          private final String selectStatement;
  
          public LimitAndOffsetDecorator(SelectStatementProvider delegate) {
              parameters.putAll(delegate.getParameters());
              parameters.put("limit", limit);
              parameters.put("offset", offset);
  
              selectStatement = delegate.getSelectStatement() +
                      " LIMIT #{parameters.limit} OFFSET #{parameters.offset}";
          }
  
          @Override
          public Map<String, Object> getParameters() {
              return parameters;
          }
  
          @Override
          public String getSelectStatement() {
              return selectStatement;
          }
      }
  }