content: /*
   * Copyright © 2018-2025 Commonwealth Scientific and Industrial Research
   * Organisation (CSIRO) ABN 41 687 119 230.
   *
   * Licensed 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 au.csiro.pathling.fhirpath.comparison;
  
  import static org.apache.spark.sql.functions.lit;
  import static org.apache.spark.sql.functions.when;
  
  import jakarta.annotation.Nonnull;
  import java.util.Arrays;
  import java.util.List;
  import org.apache.spark.sql.Column;
  
  /**
   * Implementation of a Spark SQL equality for the Coding type.
   *
   * @author Piotr Szul
   */
  public class CodingEquality implements ColumnEquality {
  
  
    @Nonnull
    private static final CodingEquality INSTANCE = new CodingEquality();
  
    /**
     * Gets the singleton instance of the comparator.
     *
     * @return the singleton instance
     */
    @Nonnull
    public static CodingEquality getInstance() {
      return INSTANCE;
    }
  
    private static final List<String> EQUALITY_COLUMNS = Arrays
        .asList("system", "code", "version", "display", "userSelected");
  
    @Nonnull
    @Override
    public Column equalsTo(@Nonnull final Column left, @Nonnull final Column right) {
      return when(left.isNull().or(right.isNull()), lit(null))
          .otherwise(
              EQUALITY_COLUMNS.stream()
                  .map(f -> left.getField(f).eqNullSafe(right.getField(f)))
                  .reduce(Column::and).orElseThrow(() -> new AssertionError("No fields to compare"))
          );
    }
  }
  