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.function;
  
  import au.csiro.pathling.fhirpath.collection.Collection;
  import jakarta.annotation.Nonnull;
  import java.util.function.Function;
  
  /**
   * Represents a transformation from one {@link Collection} to another.
   *
   * @author Piotr Szul
   */
  @FunctionalInterface
  public interface CollectionTransform extends Function<Collection, Collection> {
  
    /**
     * Ensures that the result of the transformation is a singleton boolean collection.
     *
     * @return the {@link CollectionTransform} that is guaranteed to return a singleton boolean
     * collection (or throws an evaluation error if the input collection cannot be coerced to a
     * boolean singleton).
     */
    default CollectionTransform requireBooleanSingleton() {
      return input -> apply(input).asBooleanSingleton();
    }
  
    /**
     * @param input the input collection
     * @return a function that applies the transformation and returns the column representation
     */
    default ColumnTransform toColumnTransformation(
        @Nonnull final Collection input) {
      // The type of the element Collection needs to be the same as the input.
      return c -> apply(input.copyWith(c)).getColumn();
    }
  
  }
  