package org.apache.avro;
   
   import com.fasterxml.jackson.core.JsonGenerator;
   import com.fasterxml.jackson.databind.JsonNode;
   import java.io.IOException;
   import java.util.function.Function;
   import javax.annotation.Nonnull;
   import javax.annotation.Nullable;
   
  /**
   * @author Zoltan Farkas
   */
  public interface SchemaResolver {
  
    /**
     * Lower level resolver implementation, that will write a schema in a "custom way"
     * @param schema
     * @param gen
     * @return
     * @throws IOException
     */
    default boolean customWrite(Schema schema, JsonGenerator gen) throws IOException {
      String ref = getId(schema);
      if (ref != null) {
          gen.writeStartObject();
          gen.writeFieldName(getJsonAttrName());
          gen.writeString(ref);
          gen.writeEndObject();
          return true;
      } else {
        return false;
      }
    }
  
    /**
     * Lowere level resolver implementation that will read a schema from a "custom way"
     * @param object
     * @return
     */
    @Nullable
    default Schema customRead(Function<String, JsonNode> object) {
      JsonNode refVal = object.apply(getJsonAttrName());
      if (refVal != null) {
        return resolveSchema(refVal.asText());
      } else {
        return null;
      }
    }
  
    default String getJsonAttrName() {
      return "$ref";
    }
  
    @Nonnull
    Schema resolveSchema(String id);
  
    @Nullable
    String getId(Schema schema);
  
    SchemaResolver NONE = new SchemaResolver() {
      @Override
      public Schema resolveSchema(final String id) {
        throw new UnsupportedOperationException();
      }
  
      @Override
      public String getId(final Schema schema) {
        return null;
      }
    };
  
    default void registerAsDefault() {
      SchemaResolvers.registerDefault(this);
    }
  
  }