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.rel.metadata;
  
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.TableScan;
  import org.apache.calcite.sql.SqlExplainLevel;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * RelMdExplainVisibility supplies a default implementation of
   * {@link RelMetadataQuery#isVisibleInExplain} for the standard logical algebra.
   */
  public class RelMdExplainVisibility
      implements MetadataHandler<BuiltInMetadata.ExplainVisibility> {
    public static final RelMetadataProvider SOURCE =
        ReflectiveRelMetadataProvider.reflectiveSource(
            new RelMdExplainVisibility(), BuiltInMetadata.ExplainVisibility.Handler.class);
  
    //~ Constructors -----------------------------------------------------------
  
    private RelMdExplainVisibility() {}
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public MetadataDef<BuiltInMetadata.ExplainVisibility> getDef() {
      return BuiltInMetadata.ExplainVisibility.DEF;
    }
  
    /** Catch-all implementation for
     * {@link BuiltInMetadata.ExplainVisibility#isVisibleInExplain(SqlExplainLevel)},
     * invoked using reflection.
     *
     * @see org.apache.calcite.rel.metadata.RelMetadataQuery#isVisibleInExplain(RelNode, SqlExplainLevel)
     */
    public @Nullable Boolean isVisibleInExplain(RelNode rel, RelMetadataQuery mq,
        SqlExplainLevel explainLevel) {
      // no information available
      return null;
    }
  
    public @Nullable Boolean isVisibleInExplain(TableScan scan, RelMetadataQuery mq,
        SqlExplainLevel explainLevel) {
      final BuiltInMetadata.ExplainVisibility.Handler handler =
          scan.getTable().unwrap(BuiltInMetadata.ExplainVisibility.Handler.class);
      if (handler != null) {
        return handler.isVisibleInExplain(scan, mq, explainLevel);
      }
      // Fall back to the catch-all.
      return isVisibleInExplain((RelNode) scan, mq, explainLevel);
    }
  }
  