concept Entity > NamedConcept {
}

abstract concept AbstractJavaObjectEntity<A> > Entity {
  abstract A object();
  
  toString {
    S s = super.toString();
    O o = object();
    if (o != null)
      s += " " + str_pcall(o);
    ret s;
  }
}

concept TransientJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable transient A object;
}

concept PersistentJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable A object;
}

concept ConceptEntity<A extends Concept> extends AbstractJavaObjectEntity<A> {
  new Ref<A> concept;
  
  *(A concept) { this.concept.set(concept); }
  
  A object() { ret concept!; }
}

concept FieldInObjectEntity > Entity {
  new Ref<AbstractJavaObjectEntity<?>> objectEntity;
  S fieldName;
  
  *(AbstractJavaObjectEntity objectEntity, S *fieldName) {
    this.objectEntity.set(objectEntity);
  }
  
  O value() { ret !objectEntity.has() ? null : getOpt(objectEntity->object(), fieldName); }
  
  toString {
    S s = super.toString() + " " + fieldName + " in " + objectEntity;
    O value = value();
    if (value != null)
      s += appendBracketed("value of type " + className(value));
    ret s;
  }
}

concept DeclaredFieldEntity > Entity {
  Class theClass;
  S fieldName;
  
  *(Class *theClass, S *fieldName) {}
  
  Field fieldObject() { ret findFieldOfClass(theClass, fieldName); }
  
  toString {
    var fieldObject = fieldObject();
    ret super.toString() + " " + (fieldObject != null ? str(fieldObject)
      : "[field not found: " + className(theClass) + "." + fieldName + "]");
  }
}