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Base DINA API package for Java built on SpringBoot and Crnk
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package ca.gc.aafc.dina.mapper;

import ca.gc.aafc.dina.dto.ExternalRelationDto;
import ca.gc.aafc.dina.entity.DinaEntity;
import ca.gc.aafc.dina.service.DinaService;
import io.crnk.core.engine.internal.utils.PropertyUtils;
import io.crnk.core.queryspec.QuerySpec;
import lombok.AllArgsConstructor;
import lombok.NonNull;
import lombok.SneakyThrows;

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.UUID;
import java.util.function.BiFunction;
import java.util.function.Predicate;
import java.util.stream.Collectors;


/**
 * Mapping layer handles the responsibilities for dina repo mapping operations. Those
 * responsibilities are the following.
 *  *   
 *   Bean mapping from resource to entity and vise versa
 *   Returning shallow ids when returning DTOs
 *   Linking relations to database backed resources when returning entities
 *   Mapping external relations for all mapping directions
 * 
 * 
 *
 * @param  - Resource type for the mapping layer
 * @param  - Entity type for the mapping layer
 */
@AllArgsConstructor
public class DinaMappingLayer {

  private final Class resourceClass;
  private final DinaMapper dinaMapper;
  private final DinaService dinaService;
  private final DinaMappingRegistry registry;

  //private static final PersistenceUtil PERSISTENCE_UTIL = Persistence.getPersistenceUtil();

  public DinaMappingLayer(
    Class resourceClass,
    DinaService dinaService,
    DinaMapper dinaMapper
  ) {
    this(resourceClass, dinaMapper, dinaService, new DinaMappingRegistry(resourceClass));
  }

  /**
   * Returns a list of resources mapped from the given entities. Relations included in the query
   * spec are fully mapped. External relations are always mapped. Relations not included in the
   * query spec are shallow mapped (natural id only).
   *
   * @param query    - query spec of the request
   * @param entities - entities to map
   * @return - list of resources.
   */
  public List mapEntitiesToDto(@NonNull QuerySpec query, @NonNull List entities) {
    Set includedRelations = query.getIncludedRelations().stream()
      .map(ir -> ir.getAttributePath().get(0))
      .filter(Predicate.not(s -> registry.isRelationExternal(resourceClass, s))).collect(Collectors.toSet());

    Set shallowRelationsToMap = registry
      .findMappableRelationsForClass(resourceClass)
      .stream()
      .filter(rel -> includedRelations.stream().noneMatch(rel.getName()::equalsIgnoreCase))
      .collect(Collectors.toSet());

    return entities.stream()
      .map(e -> {
        // Bean mapping
        D dto = dinaMapper.toDto(e, registry.getAttributesPerClass(), includedRelations);
        // Map shallow ids fo un-included relations
        mapShallowRelations(e, dto, shallowRelationsToMap);
        // Map External Relations
        mapExternalRelationsToDto(e, dto);
        return dto;
      })
      .collect(Collectors.toList());
  }

  /**
   * Converts a resource entity into a DTO entity. Relations included in the query
   * spec are fully mapped. External relations are always mapped. Relations not included in the
   * query spec are shallow mapped (natural id only).
   * 
   * @param query
   * @param entity
   * @return DTO entity
   */
  public D mapToDto(@NonNull QuerySpec query, @NonNull E entity) {
    return mapEntitiesToDto(query, Collections.singletonList(entity)).get(0);
  }

  /**
   * Maps a given dto to a given entity. All external/internal relations are mapped, relations are
   * linked to their database backed resource if they are not external.
   *
   * @param dto    - source of the mapping
   * @param entity - target of the mapping
   * @param     dto type
   */
  public  void mapToEntity(@NonNull S dto, @NonNull E entity) {
    Set mappableRelationsForClass = registry
      .findMappableRelationsForClass(dto.getClass());
    // Bean mapping
    applySimpleMappingToEntity(dto, entity);
    // Link relations to Database backed resources
    linkRelations(entity, mappableRelationsForClass);
  }

  /**
   * Maps a given dto to a given entity, this method will only provides a mapping of the resources attributes
   * and relationships (internal and external relations).
   *
   * @param dto    - source of the mapping
   * @param entity - target of the mapping
   * @param     dto type
   */
  public  void applySimpleMappingToEntity(S dto, E entity) {
    Set relationNames = registry
      .findMappableRelationsForClass(dto.getClass()).stream()
      .map(DinaMappingRegistry.InternalRelation::getName).collect(Collectors.toSet());
    dinaMapper.applyDtoToEntity(
      dto, entity, registry.getAttributesPerClass(), relationNames);
    // Map External Relations
    mapExternalRelationsToEntity(dto, entity);
  }

  /**
   * Returns a new dto with only the attributes mapped from a given entity.
   *
   * @param entity - source of the mapping
   * @return a new dto mapped from a given source
   */
  public D toDtoSimpleMapping(@NonNull E entity) {
    return dinaMapper.toDto(entity, registry.getAttributesPerClass(), Collections.emptySet());
  }

  /**
   * Maps the external relations from the given source to the given target
   *
   * @param source - source of the external relations
   * @param target - target of the mapping
   */
  private void mapExternalRelationsToDto(E source, D target) {
    registry.getExternalRelations(resourceClass).forEach(external -> {
      Object id = PropertyUtils.getProperty(source, external);
      if (id != null) {
        if (Collection.class.isAssignableFrom(id.getClass())) {
          PropertyUtils.setProperty(target, external,
            ((Collection) id).stream().map(ids -> ExternalRelationDto.builder()
              .type(registry.findExternalType(resourceClass, external))
              .id(ids.toString())
              .build()).collect(Collectors.toList()));
        } else {
          PropertyUtils.setProperty(target, external,
            ExternalRelationDto.builder()
              .type(registry.findExternalType(resourceClass, external))
              .id(id.toString())
              .build());
        }
      } else {
        PropertyUtils.setProperty(target, external, null);
      }
    });
  }

  /**
   * Maps the external relations from the given source to the given target.
   *
   * @param source - source of the external relations
   * @param target - target of the mapping
   */
  private void mapExternalRelationsToEntity(D source, E target) {
    registry.getExternalRelations(resourceClass).forEach(external -> {
      Object externalRelation = PropertyUtils.getProperty(source, external);
      if (externalRelation != null) {
        String jsonIdFieldName = ExternalRelationDto.ID_FIELD_NAME;
        if (Collection.class.isAssignableFrom(externalRelation.getClass())) {
          PropertyUtils.setProperty(target, external,
            ((Collection) externalRelation).stream()
              .map(rel -> UUID.fromString(PropertyUtils.getProperty(rel, jsonIdFieldName).toString()))
              .collect(Collectors.toList()));
        } else {
          PropertyUtils.setProperty(target, external,
            UUID.fromString(PropertyUtils.getProperty(externalRelation, jsonIdFieldName).toString()));
        }
      } else {
        PropertyUtils.setProperty(target, external, null);
      }
    });
  }

  /**
   * Maps the given relations from the given entity to a given dto in a shallow form (Id only).
   *
   * @param entity    - source of the mapping
   * @param dto       - target of the mapping
   * @param relations - relations to map
   */
  private void mapShallowRelations(
    @NonNull E entity,
    @NonNull D dto,
    @NonNull Set relations
  ) {
    mapRelations(entity, dto, relations,
      (aClass, relation) ->
        createShallowDTO(registry.findJsonIdFieldName(aClass), aClass, relation));
  }

  /**
   * Replaces the given relations of given entity with there JPA entity equivalent. Relations id's
   * are used to map a relation to its JPA equivalent.
   *
   * @param entity    - entity containing the relations
   * @param relations - list of relations to map
   */
  private void linkRelations(
    @NonNull E entity,
    @NonNull Set relations
  ) {
    mapRelations(entity, entity, relations,
      (aClass, relation) -> returnPersistedObject(registry.findJsonIdFieldName(aClass), relation));
  }

  /**
   * Maps the given relations from a given source to a given target with a given mapping function.
   *
   * @param source - source of the mapping
   * @param target - target of the mapping
   * @param mapper - mapping function to apply
   */
  private static void mapRelations(
    @NonNull Object source,
    @NonNull Object target,
    @NonNull Set relations,
    @NonNull BiFunction, Object, Object> mapper
  ) {
    for (DinaMappingRegistry.InternalRelation relation : relations) {
      String relationName = relation.getName();
      Class relationType = relation.getDtoType();

      // Only map the relationship if it has already been lazy loaded in #30904
      //if (PERSISTENCE_UTIL.isLoaded(source, relationName)) { see ticket
      if (relation.isCollection()) {
        Collection relationValue = (Collection) PropertyUtils.getProperty(
          source, relationName);
        if (relationValue != null) {
          Collection mappedCollection = relationValue.stream()
            .map(rel -> mapper.apply(relationType, rel)).collect(Collectors.toList());
          PropertyUtils.setProperty(target, relationName, mappedCollection);
        }
      } else {
        Object relationValue = PropertyUtils.getProperty(source, relationName);
        if (relationValue != null) {
          Object mappedRelation = mapper.apply(relationType, relationValue);
          PropertyUtils.setProperty(target, relationName, mappedRelation);
        }
        //    }
      }
    }
  }

  /**
   * Maps the given id field name from a given entity to a new instance of a given type.
   *
   * @param idFieldName - name of the id field for the mapping
   * @param type        - type of new instance to return with the mapping
   * @param entity      - entity with the id to map
   * @return - a new instance of a given type with a id value mapped from a given entity.
   */
  @SneakyThrows
  private static Object createShallowDTO(String idFieldName, Class type, Object entity) {
    Object shallowDTO = type.getConstructor().newInstance();
    PropertyUtils.setProperty(
      shallowDTO,
      idFieldName,
      PropertyUtils.getProperty(entity, idFieldName));
    return shallowDTO;
  }

  /**
   * Returns the jpa entity representing a given object with an id field of a given id field name.
   *
   * @param idFieldName - name of the id field
   * @param object      - object to map
   * @return - jpa entity representing a given object
   */
  private Object returnPersistedObject(String idFieldName, Object object) {
    Object relationID = PropertyUtils.getProperty(object, idFieldName);
    return dinaService.getReferenceByNaturalId(object.getClass(), relationID);
  }

}