BaseMessageDecoder.java

package nostr.event.json.codec;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import nostr.base.IDecoder;
import nostr.event.BaseMessage;
import nostr.event.message.CanonicalAuthenticationMessage;
import nostr.event.message.CloseMessage;
import nostr.event.message.EoseMessage;
import nostr.event.message.EventMessage;
import nostr.event.message.NoticeMessage;
import nostr.event.message.OkMessage;
import nostr.event.message.RelayAuthenticationMessage;
import nostr.event.message.ReqMessage;

import java.util.Map;

/**
 * @author eric
 */
@NoArgsConstructor
public class BaseMessageDecoder<T extends BaseMessage> implements IDecoder<T> {
  public static final int COMMAND_INDEX = 0;
  public static final int ARG_INDEX = 1;

  /**
   * Decodes a Nostr protocol message from its JSON representation.
   *
   * @param jsonString JSON representation of the message
   * @return decoded message
   * @throws nostr.event.json.codec.EventEncodingException if decoding fails
   */
  @Override
  public T decode(@NonNull String jsonString) throws EventEncodingException {
    ValidNostrJsonStructure validNostrJsonStructure = validateProperlyFormedJson(jsonString);
    String command = validNostrJsonStructure.getCommand();
    Object subscriptionId = validNostrJsonStructure.getSubscriptionId();

    return switch (command) {
      //          client <-> relay messages
      case "AUTH" -> {
        if (subscriptionId instanceof Map<?, ?> map) {
          yield CanonicalAuthenticationMessage.decode((Map<String, Object>) map);
        } else {
          yield RelayAuthenticationMessage.decode(subscriptionId);
        }
      }
      case "EVENT" -> EventMessage.decode(jsonString);
      //            missing client <-> relay handlers
      //            case "COUNT" -> CountMessage.decode(subscriptionId);

      //            client -> relay messages
      case "CLOSE" -> CloseMessage.decode(subscriptionId);
      case "REQ" -> ReqMessage.decode(subscriptionId, jsonString);

      //            relay -> client handlers
      case "EOSE" -> EoseMessage.decode(subscriptionId);
      case "NOTICE" -> NoticeMessage.decode(subscriptionId);
      case "OK" -> OkMessage.decode(jsonString);
      //            missing relay -> client handlers
      //            case "CLOSED" -> Closed.message.decode(subscriptionId);

      default ->
          throw new IllegalArgumentException(
              String.format("Invalid JSON command [%s] in JSON string [%s] ", command, jsonString));
    };
  }

  private ValidNostrJsonStructure validateProperlyFormedJson(@NonNull String jsonString)
      throws EventEncodingException {
    try {
      JsonNode root = I_DECODER_MAPPER_BLACKBIRD.readTree(jsonString);
      JsonNode commandNode = root.get(COMMAND_INDEX);
      JsonNode argNode = root.get(ARG_INDEX);

      if (commandNode == null || argNode == null) {
        String missingFields =
            (commandNode == null ? "commandNode" : "")
                + (commandNode == null && argNode == null ? " and " : "")
                + (argNode == null ? "argNode" : "");
        throw new IllegalArgumentException(
            String.format(
                "Invalid JSON structure: Missing %s in JSON string [%s]",
                missingFields, jsonString));
      }

      return new ValidNostrJsonStructure(commandNode.asText(), argNode.asText());
    } catch (JsonProcessingException e) {
      throw new EventEncodingException("Failed to decode message", e);
    }
  }

  private record ValidNostrJsonStructure(
      @NonNull String getCommand, @NonNull Object getSubscriptionId) {}
}