content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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.calcite.adapter.file;
  
  import org.apache.calcite.plan.RelOptRuleCall;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.logical.LogicalProject;
  import org.apache.calcite.rex.RexInputRef;
  import org.apache.calcite.rex.RexNode;
  
  import org.immutables.value.Value;
  
  import java.util.List;
  
  /**
   * Planner rule that projects from a {@link CsvTableScan} scan just the columns
   * needed to satisfy a projection. If the projection's expressions are trivial,
   * the projection is removed.
   *
   * @see FileRules#PROJECT_SCAN
   */
  @Value.Enclosing
  public class CsvProjectTableScanRule
      extends RelRule<CsvProjectTableScanRule.Config> {
  
    /** Creates a CsvProjectTableScanRule. */
    protected CsvProjectTableScanRule(Config config) {
      super(config);
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final LogicalProject project = call.rel(0);
      final CsvTableScan scan = call.rel(1);
      int[] fields = getProjectFields(project.getProjects());
      if (fields == null) {
        // Project contains expressions more complex than just field references.
        return;
      }
      call.transformTo(
          new CsvTableScan(
              scan.getCluster(),
              scan.getTable(),
              scan.csvTable,
              fields));
    }
  
    private static int[] getProjectFields(List<RexNode> exps) {
      final int[] fields = new int[exps.size()];
      for (int i = 0; i < exps.size(); i++) {
        final RexNode exp = exps.get(i);
        if (exp instanceof RexInputRef) {
          fields[i] = ((RexInputRef) exp).getIndex();
        } else {
          return null; // not a simple projection
        }
      }
      return fields;
    }
  
    /** Rule configuration. */
    @Value.Immutable(singleton = false)
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableCsvProjectTableScanRule.Config.builder()
          .withOperandSupplier(b0 ->
              b0.operand(LogicalProject.class).oneInput(b1 ->
                  b1.operand(CsvTableScan.class).noInputs()))
          .build();
  
      @Override default CsvProjectTableScanRule toRule() {
        return new CsvProjectTableScanRule(this);
      }
    }
  }
  