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.schema.impl;
  
  import org.apache.calcite.linq4j.tree.Expression;
  import org.apache.calcite.rel.type.RelProtoDataType;
  import org.apache.calcite.schema.Function;
  import org.apache.calcite.schema.Schema;
  import org.apache.calcite.schema.SchemaFactory;
  import org.apache.calcite.schema.SchemaPlus;
  import org.apache.calcite.schema.SchemaVersion;
  import org.apache.calcite.schema.Schemas;
  import org.apache.calcite.schema.Table;
  import org.apache.calcite.schema.lookup.CompatibilityLookup;
  import org.apache.calcite.schema.lookup.Lookup;
  import org.apache.calcite.util.LazyReference;
  
  import com.google.common.collect.ImmutableMap;
  import com.google.common.collect.ImmutableMultimap;
  import com.google.common.collect.Multimap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Collection;
  import java.util.Map;
  import java.util.Set;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Abstract implementation of {@link Schema}.
   *
   * <p>Behavior is as follows:
   * <ul>
   *   <li>The schema has no tables unless you override
   *       {@link #getTableMap()}.</li>
   *   <li>The schema has no functions unless you override
   *       {@link #getFunctionMultimap()}.</li>
   *   <li>The schema has no sub-schemas unless you override
   *       {@link #getSubSchemaMap()}.</li>
   *   <li>The schema is mutable unless you override
   *       {@link #isMutable()}.</li>
   *   <li>The name and parent schema are as specified in the constructor
   *       arguments.</li>
   * </ul>
   */
  public class AbstractSchema implements Schema {
  
    private LazyReference<Lookup<Table>> tables = new LazyReference<>();
    private LazyReference<Lookup<Schema>> subSchemas = new LazyReference<>();
  
    @Override public Lookup<Table> tables() {
      return tables.getOrCompute(
          () -> new CompatibilityLookup<>(this::getTable, this::getTableNames));
    }
  
    @Override public Lookup<? extends Schema> subSchemas() {
      return subSchemas.getOrCompute(
          () -> new CompatibilityLookup<>(this::getSubSchema, this::getSubSchemaNames));
    }
  
    @Override public boolean isMutable() {
      return true;
    }
  
    @Override public Schema snapshot(SchemaVersion version) {
      return this;
    }
  
    @Override public Expression getExpression(@Nullable SchemaPlus parentSchema, String name) {
      requireNonNull(parentSchema, "parentSchema");
      return Schemas.subSchemaExpression(parentSchema, name, getClass());
    }
  
    /**
     * Returns a map of tables in this schema by name.
     *
     * <p>The implementations of {@link #getTableNames()}
     * and {@link #getTable(String)} depend on this map.
     * The default implementation of this method returns the empty map.
     * Override this method to change their behavior.
     *
     * @return Map of tables in this schema by name
     */
    protected Map<String, Table> getTableMap() {
      return ImmutableMap.of();
    }
  
    @Deprecated @Override public final Set<String> getTableNames() {
      //noinspection RedundantCast
      return (Set<String>) getTableMap().keySet();
    }
  
    @Deprecated @Override public final @Nullable Table getTable(String name) {
      return getTableMap().get(name);
    }
  
    /**
     * Returns a map of types in this schema by name.
     *
     * <p>The implementations of {@link #getTypeNames()}
     * and {@link #getType(String)} depend on this map.
     * The default implementation of this method returns the empty map.
     * Override this method to change their behavior.
     *
     * @return Map of types in this schema by name
     */
    protected Map<String, RelProtoDataType> getTypeMap() {
      return ImmutableMap.of();
    }
  
    @Override public @Nullable RelProtoDataType getType(String name) {
      return getTypeMap().get(name);
    }
  
    @Override public Set<String> getTypeNames() {
      //noinspection RedundantCast
      return (Set<String>) getTypeMap().keySet();
    }
  
    /**
     * Returns a multi-map of functions in this schema by name.
     * It is a multi-map because functions are overloaded; there may be more than
     * one function in a schema with a given name (as long as they have different
     * parameter lists).
     *
     * <p>The implementations of {@link #getFunctionNames()}
     * and {@link Schema#getFunctions(String)} depend on this map.
     * The default implementation of this method returns the empty multi-map.
     * Override this method to change their behavior.
     *
     * @return Multi-map of functions in this schema by name
     */
    protected Multimap<String, Function> getFunctionMultimap() {
      return ImmutableMultimap.of();
    }
  
    @Override public final Collection<Function> getFunctions(String name) {
      return getFunctionMultimap().get(name); // never null
    }
  
    @Override public final Set<String> getFunctionNames() {
      return getFunctionMultimap().keySet();
    }
  
    /**
     * Returns a map of sub-schemas in this schema by name.
     *
     * <p>The implementations of {@link #getSubSchemaNames()}
     * and {@link #getSubSchema(String)} depend on this map.
     * The default implementation of this method returns the empty map.
     * Override this method to change their behavior.
     *
     * @return Map of sub-schemas in this schema by name
     */
    protected Map<String, Schema> getSubSchemaMap() {
      return ImmutableMap.of();
    }
  
    @Deprecated @Override public final Set<String> getSubSchemaNames() {
      //noinspection RedundantCast
      return (Set<String>) getSubSchemaMap().keySet();
    }
  
    @Deprecated @Override public final @Nullable Schema getSubSchema(String name) {
      return getSubSchemaMap().get(name);
    }
  
    /** Schema factory that creates an
     * {@link org.apache.calcite.schema.impl.AbstractSchema}. */
    public static class Factory implements SchemaFactory {
      public static final Factory INSTANCE = new Factory();
  
      private Factory() {}
  
      @Override public Schema create(SchemaPlus parentSchema, String name,
          Map<String, Object> operand) {
        return new AbstractSchema();
      }
    }
  }
  