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.config;
  
  /** Strategy for how NULL values are to be sorted if NULLS FIRST or NULLS LAST
   * are not specified in an item in the ORDER BY clause. */
  public enum NullCollation {
    /** Nulls first for DESC, nulls last for ASC. */
    HIGH,
    /** Nulls last for DESC, nulls first for ASC. */
    LOW,
    /** Nulls first for DESC and ASC. */
    FIRST,
    /** Nulls last for DESC and ASC. */
    LAST;
  
    /** Returns whether NULL values should appear last.
     *
     * @param desc Whether sort is descending
     */
    public boolean last(boolean desc) {
      switch (this) {
      case FIRST:
        return false;
      case LAST:
        return true;
      case LOW:
        return desc;
      case HIGH:
      default:
        return !desc;
      }
    }
  
    /** Returns whether a given combination of null direction and sort order is
     * the default order of nulls returned in the ORDER BY clause. */
    public boolean isDefaultOrder(boolean nullsFirst, boolean desc) {
      final boolean asc = !desc;
      final boolean nullsLast = !nullsFirst;
  
      switch (this) {
      case FIRST:
        return nullsFirst;
      case LAST:
        return nullsLast;
      case LOW:
        return (asc && nullsFirst) || (desc && nullsLast);
      case HIGH:
        return (asc && nullsLast) || (desc && nullsFirst);
      default:
        throw new IllegalArgumentException("Unrecognized Null Collation");
      }
    }
  }
  