package com.reallifedeveloper.tools.test.database.inmemory;
   
   import java.lang.reflect.Constructor;
   import java.lang.reflect.Field;
   import java.lang.reflect.InvocationTargetException;
   import java.lang.reflect.Method;
   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Optional;
  
  import org.checkerframework.checker.nullness.qual.NonNull;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.springframework.dao.EmptyResultDataAccessException;
  import org.springframework.data.domain.Example;
  import org.springframework.data.domain.Page;
  import org.springframework.data.domain.PageImpl;
  import org.springframework.data.domain.Pageable;
  import org.springframework.data.domain.Sort;
  import org.springframework.data.repository.CrudRepository;
  import org.springframework.data.repository.PagingAndSortingRepository;
  import org.springframework.data.repository.query.QueryByExampleExecutor;
  
  import com.reallifedeveloper.tools.test.TestUtil;
  
  /**
   * An abstract helper class that implements the {@link CrudRepository} interface using an in-memory map instead of a database.
   * <p>
   * Contains useful methods for sub-classes implementing in-memory versions of repositories, such as {@link #findByField(String, Object)} and
   * {@link #findByUniqueField(String, Object)}.
   *
   * @param <T>  the type of the entities handled by this repository
   * @param <ID> the type of the entities' primary keys
   *
   * @author RealLifeDeveloper
   */
  @SuppressWarnings({ "PMD", "checkstyle:noReturnNull" }) // TODO: Consider refactoring this class using the hints from PMD
  public abstract class AbstractInMemoryCrudRepository<T, ID extends Comparable<ID>>
          implements CrudRepository<T, ID>, PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {
  
      private final Map<@NonNull ID, @NonNull T> entities = new HashMap<>();
  
      private final @Nullable PrimaryKeyGenerator<ID> primaryKeyGenerator;
  
      /**
       * Creates a new {@code InMemoryCrudRepository} with no primary key generator. If an entity with a {@code null} primary key is saved, an
       * exception is thrown.
       */
      public AbstractInMemoryCrudRepository() {
          this.primaryKeyGenerator = null;
      }
  
      /**
       * Creates a new {@code InMemoryCrudRepository} with the provided primary key generator. If an entity with a {@code null} primary key is
       * saved, the generator is used to create a new primary key that is stored in the entity before saving.
       *
       * @param primaryKeyGenerator the primary key generator to use, must not be {@code null}
       */
      public AbstractInMemoryCrudRepository(PrimaryKeyGenerator<ID> primaryKeyGenerator) {
          if (primaryKeyGenerator == null) {
              throw new IllegalArgumentException("primaryKeyGenerator must not be null");
          }
          this.primaryKeyGenerator = primaryKeyGenerator;
      }
  
      /**
       * Finds entities with a field matching a value.
       *
       * @param fieldName the name of the field to use when searching
       * @param value     the value to search for
       * @param <F>       the type of {@code value}
       * @return a list of entities {@code e} such that {@code value.equals(e.fieldName)}
       *
       * @throws IllegalArgumentException if {@code fieldName} is {@code null}
       */
      protected <F> List<@NonNull T> findByField(String fieldName, F value) {
          if (fieldName == null) {
              throw new IllegalArgumentException("fieldName must not be null");
          }
          return entities.values().stream().filter(entity -> Objects.equals(value, TestUtil.getFieldValue(entity, fieldName))).toList();
      }
  
      /**
       * Finds a unique entity with a field matching a value.
       *
       * @param fieldName the name of the field to use when searching
       * @param value     the value to search for
       * @param <F>       the type of {@code value}
       *
       * @return the unique entity {@code e} such that {@code value.equals(e.fieldName)}, or {@code null} if no such entity is found
       *
       * @throws IllegalArgumentException if either argument is {@code null}, or if more than one entity with the given value is found
       */
      protected <F> Optional<T> findByUniqueField(String fieldName, F value) {
          List<T> foundEntities = findByField(fieldName, value);
          if (foundEntities.isEmpty()) {
             return Optional.empty();
         } else if (foundEntities.size() == 1) {
             return Optional.of(foundEntities.get(0));
         } else {
             throw new IllegalArgumentException(
                     "Field " + fieldName + " is not unique, found " + foundEntities.size() + " entities: " + foundEntities);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public long count() {
         return entities.size();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void deleteById(ID id) {
         if (id == null) {
             throw new IllegalArgumentException("id must not be null");
         }
         T removedEntity = entities.remove(id);
         if (removedEntity == null) {
             throw new EmptyResultDataAccessException("Entity with id " + id + " not found", 1);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void deleteAll(Iterable<? extends T> entitiesToDelete) {
         if (entitiesToDelete == null) {
             throw new IllegalArgumentException("entitiesToDelete must not be null");
         }
         for (T entity : entitiesToDelete) {
             delete(entity);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void deleteAllById(Iterable<? extends ID> ids) {
         for (ID id : ids) {
             deleteById(id);
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void delete(T entity) {
         if (entity == null) {
             throw new IllegalArgumentException("entity must not be null");
         }
         entities.remove(getId(entity));
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void deleteAll() {
         entities.clear();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean existsById(ID id) {
         if (id == null) {
             throw new IllegalArgumentException("id must not be null");
         }
         return entities.containsKey(id);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public List<T> findAll() {
         return new ArrayList<>(entities.values());
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public List<T> findAllById(Iterable<ID> ids) {
         if (ids == null) {
             throw new IllegalArgumentException("ids must not be null");
         }
         List<T> selectedEntities = new ArrayList<T>();
         for (ID id : ids) {
             Optional<T> optionalEntity = findById(id);
             if (optionalEntity.isPresent()) {
                 selectedEntities.add(optionalEntity.get());
             }
         }
         return selectedEntities;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Optional<T> findById(ID id) {
         if (id == null) {
             throw new IllegalArgumentException("id must not be null");
         }
         T item = entities.get(id);
         return Optional.ofNullable(item);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public <S extends T> S save(S entity) {
         if (entity == null) {
             throw new IllegalArgumentException("entity must not be null");
         }
         ID id = getId(entity);
         if (id == null) {
             if (primaryKeyGenerator != null) {
                 id = primaryKeyGenerator.nextPrimaryKey(maximumPrimaryKey());
                 setId(entity, id);
             } else {
                 throw new IllegalStateException("Primary key is null and no primary key generator available: entity=" + entity);
             }
         }
         entities.put(id, entity);
         return entity;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public <S extends T> List<S> saveAll(Iterable<S> entitiesToSave) {
         if (entitiesToSave == null) {
             throw new IllegalArgumentException("entitiesToSave must not be null");
         }
         List<S> savedEntities = new ArrayList<>();
         for (S entity : entitiesToSave) {
             savedEntities.add(save(entity));
         }
         return savedEntities;
     }
 
     //
     // PagingAndSortingRepository methods
     //
 
     /**
      * {@inheritDoc}
      */
     @Override
     public List<T> findAll(Sort sort) {
         return SortUtil.sort(findAll(), sort);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Page<T> findAll(Pageable pageable) {
         List<T> allEntities = SortUtil.sort(findAll(), pageable.getSort());
         int start = (int) pageable.getOffset();
         int end = (start + pageable.getPageSize()) > allEntities.size() ? allEntities.size() : (start + pageable.getPageSize());
         List<T> pagedEntities = start <= end ? allEntities.subList(start, end) : Collections.emptyList();
         Page<T> page = new PageImpl<>(pagedEntities, pageable, allEntities.size());
         return page;
     }
 
     //
     // Helper methods
     //
 
     private ID maximumPrimaryKey() {
         ID max = null;
         for (T entity : findAll()) {
             ID id = getId(entity);
             if (max == null || id.compareTo(max) > 0) {
                 max = id;
             }
         }
         return max;
     }
 
     /**
      * Gives the value of the ID field or method of the given entity.
      *
      * @param entity the entity to examine, should not be {@code null}
      *
      * @return the value of the ID field or method of {@code entity}, may be {@code null}
      */
     @SuppressWarnings("unchecked")
     protected @Nullable ID getId(T entity) {
         ID id = null;
         try {
             if (getIdClass(entity).isPresent()) {
                 // TODO: Handle IdClass with method annotations
                 List<Field> idFields = getIdFields(entity);
                 id = createIdClassInstance(entity, idFields);
             } else if (getIdField(entity).isPresent()) {
                 id = (ID) getIdField(entity).get().get(entity);
             } else if (getIdMethod(entity).isPresent()) {
                 id = (ID) getIdMethod(entity).get().invoke(entity);
             } else {
                 throw new IllegalArgumentException("Entity has no @Id annotation: " + entity);
             }
         } catch (ReflectiveOperationException e) {
             throw new IllegalStateException(e);
         }
         return id;
     }
 
     /**
      * Sets the value of the ID field, or calls the ID setter method, for the given entity.
      *
      * @param entity the entity for which to set the ID
      * @param id     the new ID value
      */
     protected void setId(T entity, ID id) {
         try {
             if (getIdClass(entity).isPresent()) {
                 // TODO: Handle IdClass with method annotations
                 List<Field> idFields = getIdFields(entity);
                 setIdFieldsFromIdClassInstance(entity, idFields, id);
             } else if (getIdField(entity).isPresent()) {
                 getIdField(entity).get().set(entity, id);
             } else if (getIdMethod(entity).isPresent()) {
                 Method setMethod = getSetMethod(entity, id);
                 setMethod.invoke(entity, id);
             }
         } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
             throw new IllegalStateException(e);
         }
     }
 
     private Optional<Field> getIdField(T entity) {
         List<Field> idFields = getIdFields(entity);
         if (idFields.isEmpty()) {
             return Optional.empty();
         } else if (idFields.size() > 1) {
             throw new IllegalStateException("Multiptle ID fields found in entity: " + entity);
         } else {
             return Optional.of(idFields.get(0));
         }
     }
 
     private List<Field> getIdFields(T entity) {
         List<Field> idFields = new ArrayList<>();
         Class<?> c = entity.getClass();
         while (c != null) {
             for (Field field : c.getDeclaredFields()) {
                 if (isIdField(field)) {
                     field.setAccessible(true);
                     idFields.add(field);
                 }
             }
             c = c.getSuperclass();
         }
         return idFields;
     }
 
     private Optional<Method> getIdMethod(T entity) {
         List<Method> idMethods = getIdMethods(entity);
         if (idMethods.isEmpty()) {
             return Optional.empty();
         } else if (idMethods.size() > 1) {
             throw new IllegalStateException("Multiptle ID methods found in entity: " + entity);
         } else {
             return Optional.of(idMethods.get(0));
         }
     }
 
     private List<Method> getIdMethods(T entity) {
         List<Method> idMethods = new ArrayList<>();
         Class<?> c = entity.getClass();
         while (c != null) {
             for (Method method : c.getDeclaredMethods()) {
                 if (isIdMethod(method)) {
                     method.setAccessible(true);
                     idMethods.add(method);
                 }
             }
             c = c.getSuperclass();
         }
         return idMethods;
     }
 
     private Method getSetMethod(T entity, ID id) throws NoSuchMethodException {
         Method getMethod = getIdMethod(entity)
                 .orElseThrow(() -> new NoSuchMethodException("Get method for ID not found: entity=" + entity));
         String setMethodName = getMethod.getName().replaceFirst("^get", "set");
         Method setMethod = entity.getClass().getMethod(setMethodName, id.getClass());
         setMethod.setAccessible(true);
         return setMethod;
     }
 
     private @Nullable ID createIdClassInstance(T entity, List<Field> idFields) throws ReflectiveOperationException {
         Class<ID> idClass = getIdClass(entity).orElseThrow(() -> new IllegalStateException("ID class not found: entity=" + entity));
         Constructor<ID> constructor = idClass.getDeclaredConstructor();
         constructor.setAccessible(true);
         ID id = constructor.newInstance();
         for (Field idField : idFields) {
             if (idField.get(entity) == null) {
                 // If any of the ID fields is null, we say that the primary key is null.
                 return null;
             }
             TestUtil.injectField(id, idField.getName(), idField.get(entity));
         }
         return id;
     }
 
     private void setIdFieldsFromIdClassInstance(T entity, List<Field> idFields, ID id) {
         for (Field idField : idFields) {
             Object value = TestUtil.getFieldValue(id, idField.getName());
             TestUtil.injectField(entity, idField.getName(), value);
         }
     }
 
     /**
      * Override this in a concrete subclass to decide if a given field is an ID field of an entity.
      *
      * @param field the field to examine
      *
      * @return {@code true} if {@code field} is an ID field, {@code false} otherwise
      */
     protected abstract boolean isIdField(Field field);
 
     /**
      * Override this in a concrete subclass to decide if a given method is a method giving the ID of an entity.
      *
      * @param method the method to examine
      *
      * @return {@code true} if {@code method} is an ID method, {@code false} otherwise
      */
     protected abstract boolean isIdMethod(Method method);
 
     /**
      * Override this in concrete subclass to give the ID class representing a composite primary key for an entity, if any.
      *
      * @param entity the entity to examine
      *
      * @return the ID class representing the composite primary key of {@code entity}, or an empty optional if there is no such class
      */
     protected abstract Optional<Class<ID>> getIdClass(Object entity);
 
     @Override
     public String toString() {
         return getClass().getSimpleName() + "{entities=" + entities + "}";
     }
 
     //
     // QueryByExampleExecutor methods
     //
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> Optional<S> findOne(Example<S> example) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> List<S> findAll(Example<S> example) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> Page<S> findAll(Example<S> example, Pageable pageable) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> List<S> findAll(Example<S> example, Sort sort) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> long count(Example<S> example) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * This method is not yet implemented, so it always throws an exception.
      *
      * @throws UnsupportedOperationException always
      */
     @Override
     public <S extends T> boolean exists(Example<S> example) {
         throw new UnsupportedOperationException("Not yet implemented");
     }
 
     /**
      * Make finalize method final to avoid "Finalizer attacks" and corresponding SpotBugs warning (CT_CONSTRUCTOR_THROW).
      *
      * @see <a href="https://wiki.sei.cmu.edu/confluence/display/java/OBJ11-J.+Be+wary+of+letting+constructors+throw+exceptions">
      *      Explanation of finalizer attack</a>
      */
     @Override
     @SuppressWarnings({ "checkstyle:NoFinalizer", "PMD.EmptyFinalizer", "PMD.EmptyMethodInAbstractClassShouldBeAbstract" })
     protected final void finalize() throws Throwable {
         // Do nothing
     }
 
 }