AbstractJsonSchema.java

/**
 * Copyright (C) 2015 Red Hat, Inc.
 *
 * 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 io.fabric8.crd.generator;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import io.fabric8.crd.generator.annotation.SchemaSwap;
import io.fabric8.crd.generator.utils.Types;
import io.fabric8.kubernetes.api.model.Duration;
import io.fabric8.kubernetes.api.model.IntOrString;
import io.fabric8.kubernetes.api.model.Quantity;
import io.sundr.builder.internal.functions.TypeAs;
import io.sundr.model.*;
import io.sundr.utils.Strings;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.*;

import static io.sundr.model.utils.Types.BOOLEAN_REF;
import static io.sundr.model.utils.Types.DOUBLE_REF;
import static io.sundr.model.utils.Types.INT_REF;
import static io.sundr.model.utils.Types.LONG_REF;
import static io.sundr.model.utils.Types.STRING_REF;
import static io.sundr.model.utils.Types.VOID;

/**
 * Encapsulates the common logic supporting OpenAPI schema generation for CRD generation.
 *
 * @param <T> the concrete type of the generated JSON Schema
 * @param <B> the concrete type of the JSON Schema builder
 */
public abstract class AbstractJsonSchema<T, B> {

  private static final Logger LOGGER = LoggerFactory.getLogger(AbstractJsonSchema.class);

  protected static final TypeDef OBJECT = TypeDef.forName(Object.class.getName());
  protected static final TypeDef QUANTITY = TypeDef.forName(Quantity.class.getName());
  protected static final TypeDef DURATION = TypeDef.forName(Duration.class.getName());
  protected static final TypeDef INT_OR_STRING = TypeDef.forName(IntOrString.class.getName());

  protected static final TypeRef OBJECT_REF = OBJECT.toReference();
  protected static final TypeRef QUANTITY_REF = QUANTITY.toReference();
  protected static final TypeRef DURATION_REF = DURATION.toReference();
  protected static final TypeRef INT_OR_STRING_REF = INT_OR_STRING.toReference();

  protected static final TypeDef DATE = TypeDef.forName(Date.class.getName());
  protected static final TypeRef DATE_REF = DATE.toReference();

  private static final String VALUE = "value";

  private static final String INT_OR_STRING_MARKER = "int_or_string";
  private static final String STRING_MARKER = "string";
  private static final String INTEGER_MARKER = "integer";
  private static final String NUMBER_MARKER = "number";
  private static final String BOOLEAN_MARKER = "boolean";

  protected static final TypeRef P_INT_REF = new PrimitiveRefBuilder().withName("int").build();
  protected static final TypeRef P_LONG_REF = new PrimitiveRefBuilder().withName("long").build();
  protected static final TypeRef P_DOUBLE_REF = new PrimitiveRefBuilder().withName("double").build();
  protected static final TypeRef P_BOOLEAN_REF = new PrimitiveRefBuilder().withName(BOOLEAN_MARKER)
      .build();

  private static final Map<TypeRef, String> COMMON_MAPPINGS = new HashMap<>();
  public static final String ANNOTATION_JSON_PROPERTY = "com.fasterxml.jackson.annotation.JsonProperty";
  public static final String ANNOTATION_JSON_PROPERTY_DESCRIPTION = "com.fasterxml.jackson.annotation.JsonPropertyDescription";
  public static final String ANNOTATION_JSON_IGNORE = "com.fasterxml.jackson.annotation.JsonIgnore";
  public static final String ANNOTATION_JSON_ANY_GETTER = "com.fasterxml.jackson.annotation.JsonAnyGetter";
  public static final String ANNOTATION_JSON_ANY_SETTER = "com.fasterxml.jackson.annotation.JsonAnySetter";
  public static final String ANNOTATION_MIN = "io.fabric8.generator.annotation.Min";
  public static final String ANNOTATION_MAX = "io.fabric8.generator.annotation.Max";
  public static final String ANNOTATION_PATTERN = "io.fabric8.generator.annotation.Pattern";
  public static final String ANNOTATION_NULLABLE = "io.fabric8.generator.annotation.Nullable";
  public static final String ANNOTATION_REQUIRED = "io.fabric8.generator.annotation.Required";
  public static final String ANNOTATION_NOT_NULL = "javax.validation.constraints.NotNull";
  public static final String ANNOTATION_SCHEMA_FROM = "io.fabric8.crd.generator.annotation.SchemaFrom";
  public static final String ANNOTATION_SCHEMA_SWAP = "io.fabric8.crd.generator.annotation.SchemaSwap";
  public static final String ANNOTATION_SCHEMA_SWAPS = "io.fabric8.crd.generator.annotation.SchemaSwaps";

  public static final String JSON_NODE_TYPE = "com.fasterxml.jackson.databind.JsonNode";

  static {
    COMMON_MAPPINGS.put(STRING_REF, STRING_MARKER);
    COMMON_MAPPINGS.put(DATE_REF, STRING_MARKER);
    COMMON_MAPPINGS.put(INT_REF, INTEGER_MARKER);
    COMMON_MAPPINGS.put(P_INT_REF, INTEGER_MARKER);
    COMMON_MAPPINGS.put(LONG_REF, INTEGER_MARKER);
    COMMON_MAPPINGS.put(P_LONG_REF, INTEGER_MARKER);
    COMMON_MAPPINGS.put(DOUBLE_REF, NUMBER_MARKER);
    COMMON_MAPPINGS.put(P_DOUBLE_REF, NUMBER_MARKER);
    COMMON_MAPPINGS.put(BOOLEAN_REF, BOOLEAN_MARKER);
    COMMON_MAPPINGS.put(P_BOOLEAN_REF, BOOLEAN_MARKER);
    COMMON_MAPPINGS.put(QUANTITY_REF, INT_OR_STRING_MARKER);
    COMMON_MAPPINGS.put(INT_OR_STRING_REF, INT_OR_STRING_MARKER);
    COMMON_MAPPINGS.put(DURATION_REF, STRING_MARKER);
  }

  public static String getSchemaTypeFor(TypeRef typeRef) {
    String type = COMMON_MAPPINGS.get(typeRef);
    if (type == null && typeRef instanceof ClassRef) { // Handle complex types
      ClassRef classRef = (ClassRef) typeRef;
      TypeDef def = Types.typeDefFrom(classRef);
      type = def.isEnum() ? STRING_MARKER : "object";
    }
    return type;
  }

  protected static class SchemaPropsOptions {
    final Optional<Double> min;
    final Optional<Double> max;
    final Optional<String> pattern;
    final boolean nullable;
    final boolean required;

    SchemaPropsOptions() {
      min = Optional.empty();
      max = Optional.empty();
      pattern = Optional.empty();
      nullable = false;
      required = false;
    }

    public SchemaPropsOptions(Optional<Double> min, Optional<Double> max, Optional<String> pattern,
        boolean nullable, boolean required) {
      this.min = min;
      this.max = max;
      this.pattern = pattern;
      this.nullable = nullable;
      this.required = required;
    }

    public Optional<Double> getMin() {
      return min;
    }

    public Optional<Double> getMax() {
      return max;
    }

    public Optional<String> getPattern() {
      return pattern;
    }

    public boolean isNullable() {
      return nullable;
    }

    public boolean getRequired() {
      return required;
    }
  }

  /**
   * Creates the JSON schema for the particular {@link TypeDef}. This is template method where
   * sub-classes are supposed to provide specific implementations of abstract methods.
   *
   * @param definition The definition.
   * @param ignore a potentially empty list of property names to ignore while generating the schema
   * @return The schema.
   */
  protected T internalFrom(TypeDef definition, String... ignore) {
    InternalSchemaSwaps schemaSwaps = new InternalSchemaSwaps();
    T ret = internalFromImpl(definition, new HashSet<>(), schemaSwaps, ignore);
    schemaSwaps.throwIfUnmatchedSwaps();
    return ret;
  }

  private static ClassRef extractClassRef(Object type) {
    if (type != null) {
      if (type instanceof ClassRef) {
        return (ClassRef) type;
      } else if (type instanceof Class) {
        return Types.typeDefFrom((Class) type).toReference();
      } else {
        throw new IllegalArgumentException("Unmanaged type passed to the annotation " + type);
      }
    } else {
      return null;
    }
  }

  private void extractSchemaSwaps(ClassRef definitionType, AnnotationRef annotation, InternalSchemaSwaps schemaSwaps) {
    String fullyQualifiedName = annotation.getClassRef().getFullyQualifiedName();
    switch (fullyQualifiedName) {
      case ANNOTATION_SCHEMA_SWAP:
        extractSchemaSwap(definitionType, annotation, schemaSwaps);
        break;
      case ANNOTATION_SCHEMA_SWAPS:
        Map<String, Object> params = annotation.getParameters();
        Object[] values = (Object[]) params.get("value");
        for (Object value : values) {
          extractSchemaSwap(definitionType, value, schemaSwaps);
        }
        break;
    }
  }

  private void extractSchemaSwap(ClassRef definitionType, Object annotation, InternalSchemaSwaps schemaSwaps) {
    if (annotation instanceof SchemaSwap) {
      SchemaSwap schemaSwap = (SchemaSwap) annotation;
      schemaSwaps.registerSwap(definitionType,
          extractClassRef(schemaSwap.originalType()),
          schemaSwap.fieldName(),
          extractClassRef(schemaSwap.targetType()));

    } else if (annotation instanceof AnnotationRef
        && ((AnnotationRef) annotation).getClassRef().getFullyQualifiedName().equals(ANNOTATION_SCHEMA_SWAP)) {
      Map<String, Object> params = ((AnnotationRef) annotation).getParameters();
      schemaSwaps.registerSwap(definitionType,
          extractClassRef(params.get("originalType")),
          (String) params.get("fieldName"),
          extractClassRef(params.getOrDefault("targetType", void.class)));

    } else {
      throw new IllegalArgumentException("Unmanaged annotation type passed to the SchemaSwaps: " + annotation);
    }
  }

  private T internalFromImpl(TypeDef definition, Set<String> visited, InternalSchemaSwaps schemaSwaps, String... ignore) {
    final B builder = newBuilder();
    Set<String> ignores = ignore.length > 0 ? new LinkedHashSet<>(Arrays.asList(ignore))
        : Collections
            .emptySet();
    List<String> required = new ArrayList<>();

    boolean preserveUnknownFields = (definition.getFullyQualifiedName() != null &&
        definition.getFullyQualifiedName().equals(JSON_NODE_TYPE));

    definition.getAnnotations().forEach(annotation -> extractSchemaSwaps(definition.toReference(), annotation, schemaSwaps));

    // index potential accessors by name for faster lookup
    final Map<String, Method> accessors = indexPotentialAccessors(definition);

    for (Property property : definition.getProperties()) {
      String name = property.getName();
      if (property.isStatic() || ignores.contains(name)) {
        LOGGER.debug("Ignoring property {}", name);
        continue;
      }

      ClassRef potentialSchemaSwap = schemaSwaps.lookupAndMark(definition.toReference(), name).orElse(null);
      final PropertyFacade facade = new PropertyFacade(property, accessors, potentialSchemaSwap);
      final Property possiblyRenamedProperty = facade.process();
      name = possiblyRenamedProperty.getName();

      if (facade.required) {
        required.add(name);
      } else if (facade.ignored) {
        continue;
      }
      final T schema = internalFromImpl(name, possiblyRenamedProperty.getTypeRef(), visited, schemaSwaps);
      if (facade.preserveUnknownFields) {
        preserveUnknownFields = true;
      }

      // if we got a description from the field or an accessor, use it
      final String description = facade.description;
      final T possiblyUpdatedSchema;
      if (description == null) {
        possiblyUpdatedSchema = schema;
      } else {
        possiblyUpdatedSchema = addDescription(schema, description);
      }

      SchemaPropsOptions options = new SchemaPropsOptions(
          facade.min,
          facade.max,
          facade.pattern,
          facade.nullable,
          facade.required);

      addProperty(possiblyRenamedProperty, builder, possiblyUpdatedSchema, options);
    }

    return build(builder, required, preserveUnknownFields);
  }

  private Map<String, Method> indexPotentialAccessors(TypeDef definition) {
    final List<Method> methods = definition.getMethods();
    final Map<String, Method> accessors = new HashMap<>(methods.size());
    methods.stream()
        .filter(this::isPotentialAccessor)
        .forEach(m -> accessors.put(m.getName(), m));
    return accessors;
  }

  private static class PropertyOrAccessor {
    private final Collection<AnnotationRef> annotations;
    private final String name;
    private final String propertyName;
    private final String type;
    private String renamedTo;
    private Optional<Double> min;
    private Optional<Double> max;
    private Optional<String> pattern;
    private boolean nullable;
    private boolean required;
    private boolean ignored;
    private boolean preserveUnknownFields;
    private String description;
    private TypeRef schemaFrom;

    private PropertyOrAccessor(Collection<AnnotationRef> annotations, String name, String propertyName, boolean isMethod) {
      this.annotations = annotations;
      this.name = name;
      this.propertyName = propertyName;
      type = isMethod ? "accessor" : "field";

      min = Optional.empty();
      max = Optional.empty();
      pattern = Optional.empty();
    }

    static PropertyOrAccessor fromProperty(Property property) {
      return new PropertyOrAccessor(property.getAnnotations(), property.getName(), property.getName(), false);
    }

    static PropertyOrAccessor fromMethod(Method method, String propertyName) {
      return new PropertyOrAccessor(method.getAnnotations(), method.getName(), propertyName, true);
    }

    public void process() {
      annotations.forEach(a -> {
        switch (a.getClassRef().getFullyQualifiedName()) {
          case ANNOTATION_NULLABLE:
            nullable = true;
            break;
          case ANNOTATION_MAX:
            max = Optional.of((Double) a.getParameters().get(VALUE));
            break;
          case ANNOTATION_MIN:
            min = Optional.of((Double) a.getParameters().get(VALUE));
            break;
          case ANNOTATION_PATTERN:
            pattern = Optional.of((String) a.getParameters().get(VALUE));
            break;
          case ANNOTATION_NOT_NULL:
            LOGGER.warn("Annotation: {} on property: {} is deprecated. Please use: {} instead", ANNOTATION_NOT_NULL, name,
                ANNOTATION_REQUIRED);
            required = true;
            break;
          case ANNOTATION_REQUIRED:
            required = true;
            break;
          case ANNOTATION_JSON_PROPERTY:
            final String nameFromAnnotation = (String) a.getParameters().get(VALUE);
            if (!Strings.isNullOrEmpty(nameFromAnnotation) && !propertyName.equals(nameFromAnnotation)) {
              renamedTo = nameFromAnnotation;
            }
            break;
          case ANNOTATION_JSON_PROPERTY_DESCRIPTION:
            final String descriptionFromAnnotation = (String) a.getParameters().get(VALUE);
            if (!Strings.isNullOrEmpty(descriptionFromAnnotation)) {
              description = descriptionFromAnnotation;
            }
            break;
          case ANNOTATION_JSON_IGNORE:
            ignored = true;
            break;
          case ANNOTATION_JSON_ANY_GETTER:
          case ANNOTATION_JSON_ANY_SETTER:
            preserveUnknownFields = true;
            break;
          case ANNOTATION_SCHEMA_FROM:
            schemaFrom = extractClassRef(a.getParameters().get("type"));
            break;
        }
      });
    }

    public String getRenamedTo() {
      return renamedTo;
    }

    public boolean isNullable() {
      return nullable;
    }

    public Optional<Double> getMax() {
      return max;
    }

    public Optional<Double> getMin() {
      return min;
    }

    public Optional<String> getPattern() {
      return pattern;
    }

    public boolean isRequired() {
      return required;
    }

    public boolean isIgnored() {
      return ignored;
    }

    public boolean isPreserveUnknownFields() {
      return preserveUnknownFields;
    }

    public String getDescription() {
      return description;
    }

    public boolean contributeName() {
      return renamedTo != null;
    }

    public boolean contributeDescription() {
      return description != null;
    }

    public TypeRef getSchemaFrom() {
      return schemaFrom;
    }

    public boolean contributeSchemaFrom() {
      return schemaFrom != null;
    }

    @Override
    public String toString() {
      return "'" + name + "' " + type;
    }
  }

  private static class PropertyFacade {
    private final List<PropertyOrAccessor> propertyOrAccessors = new ArrayList<>(4);
    private String renamedTo;
    private String description;
    private Optional<Double> min;
    private Optional<Double> max;
    private Optional<String> pattern;
    private boolean nullable;
    private boolean required;
    private boolean ignored;
    private boolean preserveUnknownFields;
    private final Property original;
    private String nameContributedBy;
    private String descriptionContributedBy;
    private TypeRef schemaFrom;

    public PropertyFacade(Property property, Map<String, Method> potentialAccessors, ClassRef schemaSwap) {
      original = property;
      final String capitalized = property.getNameCapitalized();
      final String name = property.getName();
      propertyOrAccessors.add(PropertyOrAccessor.fromProperty(property));
      Method method = potentialAccessors.get("is" + capitalized);
      if (method != null) {
        propertyOrAccessors.add(PropertyOrAccessor.fromMethod(method, name));
      }
      method = potentialAccessors.get("get" + capitalized);
      if (method != null) {
        propertyOrAccessors.add(PropertyOrAccessor.fromMethod(method, name));
      }
      method = potentialAccessors.get("set" + capitalized);
      if (method != null) {
        propertyOrAccessors.add(PropertyOrAccessor.fromMethod(method, name));
      }
      schemaFrom = schemaSwap;
      min = Optional.empty();
      max = Optional.empty();
      pattern = Optional.empty();
    }

    public Property process() {
      final String name = original.getName();

      propertyOrAccessors.forEach(p -> {
        p.process();
        final String contributorName = p.toString();
        if (p.contributeName()) {
          if (renamedTo == null) {
            renamedTo = p.getRenamedTo();
            this.nameContributedBy = contributorName;
          } else {
            LOGGER.debug("Property {} has already been renamed to {} by {}", name, renamedTo, nameContributedBy);
          }
        }

        if (p.contributeDescription()) {
          if (description == null) {
            description = p.getDescription();
            descriptionContributedBy = contributorName;
          } else {
            LOGGER.debug("Description for property {} has already been contributed by: {}", name, descriptionContributedBy);
          }
        }

        if (p.getMin().isPresent()) {
          min = p.getMin();
        }

        if (p.getMax().isPresent()) {
          max = p.getMax();
        }

        if (p.getPattern().isPresent()) {
          pattern = p.getPattern();
        }

        if (p.isNullable()) {
          nullable = true;
        }

        if (p.isRequired()) {
          required = true;
        } else if (p.isIgnored()) {
          ignored = true;
        }

        if (p.isPreserveUnknownFields()) {
          preserveUnknownFields = true;
        }

        if (p.contributeSchemaFrom()) {
          schemaFrom = p.getSchemaFrom();
        }
      });

      TypeRef typeRef = schemaFrom != null ? schemaFrom : original.getTypeRef();
      String finalName = renamedTo != null ? renamedTo : original.getName();

      return new Property(original.getAnnotations(), typeRef, finalName,
          original.getComments(), original.getModifiers(), original.getAttributes());
    }
  }

  private boolean isPotentialAccessor(Method method) {
    final String name = method.getName();
    return name.startsWith("is") || name.startsWith("get") || name.startsWith("set");
  }

  /**
   * Retrieves the updated property name for the specified property if its annotations warrant it
   *
   * @param property the Property which name might need to be updated
   * @return the updated property name or its original one if it didn't need to be changed
   */
  private String extractUpdatedNameFromJacksonPropertyIfPresent(Property property) {
    final String name = property.getName();
    final boolean ignored = property.getAnnotations().stream()
        .anyMatch(a -> a.getClassRef().getFullyQualifiedName().equals(ANNOTATION_JSON_IGNORE));

    if (ignored) {
      return "$" + property.getName();
    } else {
      return property.getAnnotations().stream()
          // only consider JsonProperty annotation
          .filter(a -> a.getClassRef().getFullyQualifiedName().equals(ANNOTATION_JSON_PROPERTY))
          .findAny()
          // if we found an annotated accessor, override the property's name if needed
          .map(a -> {
            final String fromAnnotation = (String) a.getParameters().get(VALUE);
            if (!Strings.isNullOrEmpty(fromAnnotation) && !name.equals(fromAnnotation)) {
              return fromAnnotation;
            } else {
              return name;
            }
          }).orElse(property.getName());
    }
  }

  /**
   * Creates a new specific builder object.
   *
   * @return a new builder object specific to the CRD generation version
   */
  public abstract B newBuilder();

  /**
   * Adds the specified property to the specified builder, calling {@link #internalFrom(String, TypeRef)}
   * to create the property schema.
   *
   * @param property the property to add to the currently being built schema
   * @param builder the builder representing the schema being built
   * @param schema the built schema for the property being added
   */
  public abstract void addProperty(Property property, B builder, T schema, SchemaPropsOptions options);

  /**
   * Finishes up the process by actually building the final JSON schema based on the provided
   * builder and a potentially empty list of names of fields which should be marked as required
   *
   * @param builder the builder used to build the final schema
   * @param required the list of names of required fields
   * @return the built JSON schema
   */
  public abstract T build(B builder, List<String> required, boolean preserveUnknownFields);

  /**
   * Builds the specific JSON schema representing the structural schema for the specified property
   *
   * @param name the name of the property which schema we want to build
   * @param typeRef the type of the property which schema we want to build
   * @return the structural schema associated with the specified property
   */
  public T internalFrom(String name, TypeRef typeRef) {
    return internalFromImpl(name, typeRef, new HashSet<>(), new InternalSchemaSwaps());
  }

  private T internalFromImpl(String name, TypeRef typeRef, Set<String> visited, InternalSchemaSwaps schemaSwaps) {
    // Note that ordering of the checks here is meaningful: we need to check for complex types last
    // in case some "complex" types are handled specifically
    if (typeRef.getDimensions() > 0 || io.sundr.model.utils.Collections.isCollection(typeRef)) { // Handle Collections & Arrays
      final TypeRef collectionType = TypeAs.combine(TypeAs.UNWRAP_ARRAY_OF, TypeAs.UNWRAP_COLLECTION_OF)
          .apply(typeRef);
      final T schema = internalFromImpl(name, collectionType, visited, schemaSwaps);
      return arrayLikeProperty(schema);
    } else if (io.sundr.model.utils.Collections.IS_MAP.apply(typeRef)) { // Handle Maps
      final TypeRef keyType = TypeAs.UNWRAP_MAP_KEY_OF.apply(typeRef);

      if (!(keyType instanceof ClassRef && ((ClassRef) keyType).getFullyQualifiedName().equals("java.lang.String"))) {
        LOGGER.warn("Property '{}' with '{}' key type is mapped to 'string' because of CRD schemas limitations", name, typeRef);
      }

      final TypeRef valueType = TypeAs.UNWRAP_MAP_VALUE_OF.apply(typeRef);
      T schema = internalFromImpl(name, valueType, visited, schemaSwaps);
      if (schema == null) {
        LOGGER.warn(
            "Property '{}' with '{}' value type is mapped to 'object' because its CRD representation cannot be extracted.",
            name, typeRef);
        schema = internalFromImpl(name, OBJECT_REF, visited, schemaSwaps);
      }

      return mapLikeProperty(schema);
    } else if (io.sundr.model.utils.Optionals.isOptional(typeRef)) { // Handle Optionals
      return internalFromImpl(name, TypeAs.UNWRAP_OPTIONAL_OF.apply(typeRef), visited, schemaSwaps);
    } else {
      final String typeName = COMMON_MAPPINGS.get(typeRef);
      if (typeName != null) { // we have a type that we handle specifically
        if (INT_OR_STRING_MARKER.equals(typeName)) { // Handle int or string mapped types
          return mappedProperty(typeRef);
        } else {
          return singleProperty(typeName); // Handle Standard Types
        }
      } else {
        if (typeRef instanceof ClassRef) { // Handle complex types
          ClassRef classRef = (ClassRef) typeRef;
          TypeDef def = Types.typeDefFrom(classRef);

          // check if we're dealing with an enum
          if (def.isEnum()) {
            final JsonNode[] enumValues = def.getProperties().stream()
                .map(this::extractUpdatedNameFromJacksonPropertyIfPresent)
                .filter(n -> !n.startsWith("$"))
                .map(JsonNodeFactory.instance::textNode)
                .toArray(JsonNode[]::new);
            return enumProperty(enumValues);
          } else if (!classRef.getFullyQualifiedName().equals(VOID.getName())) {
            return resolveNestedClass(name, def, visited, schemaSwaps);
          }

        }
        return null;
      }
    }
  }

  // Flag to detect cycles
  private boolean resolving = false;

  private T resolveNestedClass(String name, TypeDef def, Set<String> visited, InternalSchemaSwaps schemaSwaps) {
    if (!resolving) {
      visited.clear();
      resolving = true;
    } else {
      String visitedName = name + ":" + def.getFullyQualifiedName();
      if (!def.getFullyQualifiedName().startsWith("java") && visited.contains(visitedName)) {
        throw new IllegalArgumentException(
            "Found a cyclic reference involving the field " + name + " of type " + def.getFullyQualifiedName());
      }
      visited.add(visitedName);
    }

    T res = internalFromImpl(def, visited, schemaSwaps);
    resolving = false;
    return res;
  }

  /**
   * Builds the schema for specifically handled property types (e.g. intOrString properties)
   *
   * @param ref the type of the specifically handled property
   * @return the property schema
   */
  protected abstract T mappedProperty(TypeRef ref);

  /**
   * Builds the schema for array-like properties
   *
   * @param schema the schema for the extracted element type for this array-like property
   * @return the schema for the array-like property
   */
  protected abstract T arrayLikeProperty(T schema);

  /**
   * Builds the schema for map-like properties
   *
   * @param schema the schema for the extracted element type for the values of this map-like property
   * @return the schema for the map-like property
   */
  protected abstract T mapLikeProperty(T schema);

  /**
   * Builds the schema for standard, simple (e.g. string) property types
   *
   * @param typeName the mapped name of the property type
   * @return the schema for the property
   */
  protected abstract T singleProperty(String typeName);

  protected abstract T enumProperty(JsonNode... enumValues);

  protected abstract T addDescription(T schema, String description);
}