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;
  
  import org.apache.calcite.adapter.java.JavaTypeFactory;
  import org.apache.calcite.jdbc.CalciteConnection;
  import org.apache.calcite.linq4j.QueryProvider;
  import org.apache.calcite.schema.SchemaPlus;
  
  import com.google.common.collect.ImmutableMap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.io.Serializable;
  import java.util.Map;
  import java.util.function.Function;
  
  import static java.util.Objects.requireNonNull;
  
  /** Utilities for {@link DataContext}. */
  public class DataContexts {
    private DataContexts() {
    }
  
    /** Instance of {@link DataContext} that has no variables. */
    public static final DataContext EMPTY = new EmptyDataContext();
  
    /** Returns an instance of {@link DataContext} with the given map. */
    public static DataContext of(Map<String, ?> map) {
      return new MapDataContext(map);
    }
  
    /** Returns an instance of {@link DataContext} with the given function. */
    public static DataContext of(Function<String, ? extends @Nullable Object> fn) {
      return new FunctionDataContext(fn);
    }
  
    /** Returns an instance of {@link DataContext} with the given connection
     * and root schema but no variables. */
    public static DataContext of(CalciteConnection connection,
        @Nullable SchemaPlus rootSchema) {
      return new DataContextImpl(connection, rootSchema, ImmutableMap.of());
    }
  
    /** Implementation of {@link DataContext} that has no variables.
     *
     * <p>It is {@link Serializable} for Spark's benefit. */
    private static class EmptyDataContext implements DataContext, Serializable {
      @Override public @Nullable SchemaPlus getRootSchema() {
        return null;
      }
  
      @Override public JavaTypeFactory getTypeFactory() {
        throw new UnsupportedOperationException();
      }
  
      @Override public QueryProvider getQueryProvider() {
        throw new UnsupportedOperationException();
      }
  
      @Override public @Nullable Object get(String name) {
        return null;
      }
    }
  
    /** Implementation of {@link DataContext} backed by a Map.
     *
     * <p>Keys and values in the map must not be null. Rather than storing a null
     * value for a key, remove the key from the map; the effect will be the
     * same. */
    private static class MapDataContext extends EmptyDataContext {
      private final ImmutableMap<String, ?> map;
  
      MapDataContext(Map<String, ?> map) {
        this.map = ImmutableMap.copyOf(map);
      }
  
      @Override public @Nullable Object get(String name) {
        return map.get(name);
      }
    }
  
    /** Implementation of {@link DataContext} backed by a Function. */
    private static class FunctionDataContext extends EmptyDataContext {
      private final Function<String, ? extends @Nullable Object> fn;
  
      FunctionDataContext(Function<String, ? extends @Nullable Object> fn) {
        this.fn = requireNonNull(fn, "fn");
      }
  
      @Override public @Nullable Object get(String name) {
        return fn.apply(name);
      }
    }
  
    /** Implementation of {@link DataContext} backed by a Map. */
    private static class DataContextImpl extends MapDataContext {
      private final CalciteConnection connection;
      private final @Nullable SchemaPlus rootSchema;
  
      DataContextImpl(CalciteConnection connection,
          @Nullable SchemaPlus rootSchema, Map<String, Object> map) {
        super(map);
        this.connection = requireNonNull(connection, "connection");
        this.rootSchema = requireNonNull(rootSchema, "rootSchema");
      }
  
      @Override public JavaTypeFactory getTypeFactory() {
        return connection.getTypeFactory();
      }
  
      @Override public @Nullable SchemaPlus getRootSchema() {
        return rootSchema;
      }
  
      @Override public QueryProvider getQueryProvider() {
        return connection;
      }
    }
  }
  