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.projection;
  
  import au.csiro.pathling.fhirpath.Materializable;
  import au.csiro.pathling.fhirpath.collection.Collection;
  import jakarta.annotation.Nonnull;
  import org.apache.spark.sql.Column;
  
  /**
   * The result of evaluating a {@link RequestedColumn} as part of a {@link ProjectionClause}.
   *
   * @param collection The result of evaluating the column.
   * @param requestedColumn The column that was requested to be included in the projection.
   */
  public record ProjectedColumn(
      @Nonnull Collection collection,
      @Nonnull RequestedColumn requestedColumn
  ) {
  
    /**
     * Gets the column value from the collection and aliases it with the requested name. If a SQL type
     * is specified in the requested column, the column value will be cast to that type.
     *
     * @return The column value with the appropriate alias
     */
    @Nonnull
    public Column getValue() {
      // If a type was asserted for the column, check that the collection is of that type.
      requestedColumn.type().ifPresent(requestedType ->
          collection.getFhirType().ifPresent(actualType -> {
            if (!requestedType.equals(actualType)) {
              throw new IllegalArgumentException(
                  "Collection " + collection + " has type " + actualType
                      + ", expected " + requestedType);
            }
          })
      );
      final Column rawResult = Materializable.getExternalValue(requestedColumn.collection()
                                                               ? collection.asPlural()
                                                               : collection.asSingular());
      return requestedColumn.sqlType()
          .map(rawResult::cast)
          .orElse(rawResult)
          .alias(requestedColumn.name());
  
    }
  }
  