package eu.mulk.quarkus.googlecloud.jsonlogging;

import io.smallrye.common.constraint.Nullable;
import java.time.Instant;
import java.util.List;
import java.util.Map;
import javax.json.Json;
import javax.json.JsonObject;
import javax.json.JsonObjectBuilder;

/**
 * A JSON log entry compatible with Google Cloud Logging.
 *
 * <p>Roughly (but not quite) corresponds to Google Cloud Logging's <a
 * href="https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry">LogEntry</a>
 * structure.
 *
 * <p>A few of the fields are treated specially by the fluentd instance running in Google Kubernetes
 * Engine. All other fields end up in the jsonPayload field on the Google Cloud Logging side.
 */
record LogEntry(
    String message,
    String severity,
    Timestamp timestamp,
    @Nullable String trace,
    @Nullable String spanId,
    SourceLocation sourceLocation,
    Map<String, String> labels,
    List<StructuredParameter> parameters,
    Map<String, String> mappedDiagnosticContext,
    @Nullable String nestedDiagnosticContext,
    @Nullable String type) {

  static record SourceLocation(
      @Nullable String file, @Nullable String line, @Nullable String function) {

    JsonObject json() {
      return Json.createObjectBuilder()
          .add("file", file)
          .add("line", line)
          .add("function", function)
          .build();
    }
  }

  static record Timestamp(long seconds, int nanos) {

    Timestamp(Instant t) {
      this(t.getEpochSecond(), t.getNano());
    }

    JsonObject json() {
      return Json.createObjectBuilder().add("seconds", seconds).add("nanos", nanos).build();
    }
  }

  JsonObjectBuilder json() {
    var b = Json.createObjectBuilder();

    if (trace != null) {
      b.add("trace", trace);
    }

    if (spanId != null) {
      b.add("spanId", spanId);
    }

    if (nestedDiagnosticContext != null && !nestedDiagnosticContext.isEmpty()) {
      b.add("nestedDiagnosticContext", nestedDiagnosticContext);
    }

    if (!labels.isEmpty()) {
      b.add("labels", jsonOfStringMap(labels));
    }

    if (type != null) {
      b.add("@type", type);
    }

    return b.add("message", message)
        .add("severity", severity)
        .add("timestamp", timestamp.json())
        .add("sourceLocation", sourceLocation.json())
        .addAll(jsonOfStringMap(mappedDiagnosticContext))
        .addAll(jsonOfParameterMap(parameters));
  }

  private static JsonObjectBuilder jsonOfStringMap(Map<String, String> stringMap) {
    return stringMap.entrySet().stream()
        .reduce(
            Json.createObjectBuilder(),
            (acc, x) -> acc.add(x.getKey(), x.getValue()),
            JsonObjectBuilder::addAll);
  }

  private static JsonObjectBuilder jsonOfParameterMap(List<StructuredParameter> parameters) {
    return parameters.stream()
        .reduce(
            Json.createObjectBuilder(),
            (acc, p) -> acc.addAll(p.json()),
            JsonObjectBuilder::addAll);
  }
}