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.sql.fun;
  
  import org.apache.calcite.sql.SqlOperator;
  import org.apache.calcite.sql.SqlOperatorTable;
  import org.apache.calcite.sql.util.SqlOperatorTables;
  import org.apache.calcite.util.Util;
  
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.ImmutableSet;
  
  import java.lang.reflect.Field;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Objects;
  import java.util.Set;
  import java.util.concurrent.ExecutionException;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Factory that creates operator tables that consist of functions and operators
   * for particular named libraries. For example, the following code will return
   * an operator table that contains operators for both Oracle and MySQL:
   *
   * <blockquote>
   *   <pre>SqlOperatorTable opTab =
   *     SqlLibraryOperatorTableFactory.INSTANCE.getOperatorTable(
   *         EnumSet.of(SqlLibrary.ORACLE, SqlLibrary.MYSQL))</pre>
   * </blockquote>
   *
   * <p>To define a new library, add a value to enum {@link SqlLibrary}.
   *
   * <p>To add functions to a library, add the {@link LibraryOperator} annotation
   * to fields that of type {@link SqlOperator}, and the library name to its
   * {@link LibraryOperator#libraries()} field.
   */
  public class SqlLibraryOperatorTableFactory {
  
    /** List of classes to scan for operators. */
    private final ImmutableList<Class> classes;
  
    /** The singleton instance. */
    public static final SqlLibraryOperatorTableFactory INSTANCE =
        new SqlLibraryOperatorTableFactory(SqlLibraryOperators.class);
  
    private SqlLibraryOperatorTableFactory(Class... classes) {
      this.classes = ImmutableList.copyOf(classes);
    }
  
    //~ Instance fields --------------------------------------------------------
  
    /** A cache that returns an operator table for a given library (or set of
     * libraries). */
    @SuppressWarnings("methodref.receiver.bound.invalid")
    private final LoadingCache<ImmutableSet<SqlLibrary>, SqlOperatorTable> cache =
        CacheBuilder.newBuilder().build(CacheLoader.from(this::create));
  
    //~ Methods ----------------------------------------------------------------
  
    /** Creates an operator table that contains operators in the given set of
     * libraries. */
    private SqlOperatorTable create(ImmutableSet<SqlLibrary> librarySet) {
      final List<SqlOperator> list = new ArrayList<>();
      boolean custom = false;
      boolean standard = false;
      for (SqlLibrary library : librarySet) {
        switch (library) {
        case STANDARD:
          standard = true;
          break;
        case SPATIAL:
          list.addAll(SqlOperatorTables.spatialInstance().getOperatorList());
          break;
        default:
          custom = true;
        }
      }
  
      // Use reflection to register the expressions stored in public fields.
      // Skip if the only libraries asked for are "standard" or "spatial".
      if (custom) {
        for (Class aClass : classes) {
          for (Field field : aClass.getFields()) {
            try {
              if (SqlOperator.class.isAssignableFrom(field.getType())) {
                final SqlOperator op =
                    (SqlOperator) requireNonNull(field.get(this),
                        () -> "null value of " + field + " for " + this);
                if (operatorIsInLibrary(op.getName(), field, librarySet)) {
                  list.add(op);
                }
              }
            } catch (IllegalArgumentException | IllegalAccessException e) {
              throw Util.throwAsRuntime(Util.causeOrSelf(e));
            }
          }
        }
      }
      SqlOperatorTable operatorTable = SqlOperatorTables.of(list);
      if (standard) {
        operatorTable =
            SqlOperatorTables.chain(SqlStdOperatorTable.instance(),
                operatorTable);
      }
      return operatorTable;
    }
  
    /** Returns whether an operator is in one or more of the given libraries. */
    private static boolean operatorIsInLibrary(String operatorName, Field field,
        Set<SqlLibrary> seekLibrarySet) {
      LibraryOperator libraryOperator =
          field.getAnnotation(LibraryOperator.class);
      if (libraryOperator == null) {
        throw new AssertionError("Operator must have annotation: "
            + operatorName);
      }
      SqlLibrary[] librarySet = libraryOperator.libraries();
      if (librarySet.length <= 0) {
        throw new AssertionError("Operator must belong to at least one library: "
            + operatorName);
      }
      for (SqlLibrary library : librarySet) {
        if (seekLibrarySet.contains(library)) {
          return true;
        }
        // Also check inheritor libraries (if any) that are not excluded
        for (SqlLibrary inheritor : library.inheritors()) {
          if (seekLibrarySet.contains(inheritor)
              && !arrayContains(libraryOperator.exceptLibraries(), inheritor)) {
            return true;
          }
        }
      }
      return false;
    }
  
    /** Returns whether an array contains a given element. */
    private static <E> boolean arrayContains(E[] elements, E seek) {
      for (E element : elements) {
        if (Objects.equals(element, seek)) {
          return true;
        }
      }
      return false;
    }
  
    /** Returns a SQL operator table that contains operators in the given library
     * or libraries. */
    public SqlOperatorTable getOperatorTable(SqlLibrary... libraries) {
      return getOperatorTable(ImmutableSet.copyOf(libraries));
    }
  
    /** Returns a SQL operator table that contains operators in the given set of
     * libraries. */
    public SqlOperatorTable getOperatorTable(Iterable<SqlLibrary> librarySet) {
      return getOperatorTable(librarySet, true);
    }
  
    /** Returns a SQL operator table that contains operators in the given set of
     * libraries, optionally inheriting in operators in {@link SqlLibrary#ALL}. */
    public SqlOperatorTable getOperatorTable(Iterable<SqlLibrary> librarySet,
        boolean includeAll) {
      try {
        // Expand so that 'hive' becomes 'all,hive';
        // ensures that operators with library=all get loaded.
        final List<SqlLibrary> expandedLibrarySet =
            includeAll
                ? SqlLibrary.expandUp(librarySet)
                : ImmutableList.copyOf(librarySet);
        return cache.get(ImmutableSet.copyOf(expandedLibrarySet));
      } catch (ExecutionException e) {
        throw Util.throwAsRuntime("populating SqlOperatorTable for library "
            + librarySet, Util.causeOrSelf(e));
      }
    }
  }
  