public class MySpanProcessor implements SpanProcessor {

  @Override
  public void onStart(Context parentContext, ReadWriteSpan span) {
    // Add custom attributes when span starts
    span.setAttribute("custom.processor", "active");
  }

  @Override
  public boolean isStartRequired() {
    return true;
  }

  @Override
  public void onEnd(ReadableSpan span) {
    // Process span when it ends (optional)
  }

  @Override
  public boolean isEndRequired() {
    return false;
  }

  @Override
  public CompletableResultCode shutdown() {
    return CompletableResultCode.ofSuccess();
  }
}

@AutoService(AutoConfigurationCustomizerProvider.class)
public class MyExtensionProvider implements AutoConfigurationCustomizerProvider {

  @Override
  public void customize(AutoConfigurationCustomizer config) {
    config.addTracerProviderCustomizer(this::configureTracer);
  }

  private SdkTracerProviderBuilder configureTracer(
      SdkTracerProviderBuilder tracerProvider, ConfigProperties config) {
    return tracerProvider
        .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(1024).build())
        .addSpanProcessor(new MySpanProcessor());
  }
}

@Override
public Sampler createSampler(ConfigProperties config) {
  // Read configuration with defaults
  String endpoint = config.getString("otel.exporter.otlp.endpoint", "http://localhost:4317");
  int threshold = config.getInt("otel.instrumentation.myext.threshold", 100);
  boolean enabled = config.getBoolean("otel.instrumentation.myext.enabled", true);
  return new MySampler(endpoint, threshold, enabled);
}

@Override
public void customize(AutoConfigurationCustomizer config) {
  config.addPropertiesSupplier(() -> {
    Map<String, String> props = new HashMap<>();
    props.put("otel.exporter.otlp.endpoint", "http://my-backend:8080");
    props.put("otel.service.name", "my-service");
    props.put("otel.instrumentation.myext.enabled", "true");
    return props;
  });
}

import com.google.auto.service.AutoService;

@AutoService(AutoConfigurationCustomizerProvider.class)
public class MyExtension implements AutoConfigurationCustomizerProvider {
  // Implementation
}

@AutoService(AutoConfigurationCustomizerProvider.class)
public class DemoAutoConfigurationCustomizerProvider
    implements AutoConfigurationCustomizerProvider {

  @Override
  public void customize(AutoConfigurationCustomizer autoConfiguration) {
    autoConfiguration
        .addTracerProviderCustomizer(this::configureSdkTracerProvider)
        .addPropertiesSupplier(this::getDefaultProperties);
  }

  private SdkTracerProviderBuilder configureSdkTracerProvider(
      SdkTracerProviderBuilder tracerProvider, ConfigProperties config) {

    return tracerProvider
        .setIdGenerator(new DemoIdGenerator())
        .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(1024).build())
        .addSpanProcessor(new DemoSpanProcessor())
        .addSpanProcessor(SimpleSpanProcessor.create(new DemoSpanExporter()));
  }

  private Map<String, String> getDefaultProperties() {
    Map<String, String> properties = new HashMap<>();
    properties.put("otel.exporter.otlp.endpoint", "http://backend:8080");
    properties.put("otel.exporter.otlp.insecure", "true");
    properties.put("otel.config.max.attrs", "16");
    properties.put("otel.traces.sampler", "demo");
    return properties;
  }
}

/**
 * This example demonstrates how to use the InstrumenterCustomizerProvider SPI to customize
 * instrumentation behavior without modifying the core instrumentation code.
 *
 * <p>This customizer adds:
 *
 * <ul>
 *   <li>Custom attributes to HTTP server spans (based on instrumentation name)
 *   <li>Custom attributes to HTTP client spans (based on instrumentation type)
 *   <li>Custom metrics for HTTP operations
 *   <li>Request correlation IDs via context customization
 *   <li>Custom span name transformation
 * </ul>
 *
 * <p>The customizer will be automatically applied to instrumenters that match the specified
 * instrumentation name or type.
 *
 * @see InstrumenterCustomizerProvider
 * @see InstrumenterCustomizer
 */
@AutoService(InstrumenterCustomizerProvider.class)
public class DemoInstrumenterCustomizerProvider implements InstrumenterCustomizerProvider {

  @Override
  public void customize(InstrumenterCustomizer customizer) {
    String instrumentationName = customizer.getInstrumentationName();
    if (isHttpServerInstrumentation(instrumentationName)) {
      customizeHttpServer(customizer);
    }

    if (customizer.hasType(InstrumenterCustomizer.InstrumentationType.HTTP_CLIENT)) {
      customizeHttpClient(customizer);
    }
  }

  private boolean isHttpServerInstrumentation(String instrumentationName) {
    return instrumentationName.contains("servlet")
        || instrumentationName.contains("jetty")
        || instrumentationName.contains("tomcat")
        || instrumentationName.contains("undertow")
        || instrumentationName.contains("spring-webmvc");
  }

  private void customizeHttpServer(InstrumenterCustomizer customizer) {
    customizer.addAttributesExtractor(new DemoAttributesExtractor());
    customizer.addOperationMetrics(new DemoMetrics());
    customizer.addContextCustomizer(new DemoContextCustomizer());
    customizer.setSpanNameExtractorCustomizer(
        unused -> (SpanNameExtractor<Object>) object -> "CustomHTTP/" + object.toString());
  }

  private void customizeHttpClient(InstrumenterCustomizer customizer) {
    // Simple customization for HTTP client instrumentations
    customizer.addAttributesExtractor(new DemoHttpClientAttributesExtractor());
  }

  /** Custom attributes extractor for HTTP client instrumentations. */
  private static class DemoHttpClientAttributesExtractor
      implements AttributesExtractor<Object, Object> {
    private static final AttributeKey<String> CLIENT_ATTR =
        AttributeKey.stringKey("demo.client.type");

    @Override
    public void onStart(AttributesBuilder attributes, Context context, Object request) {
      attributes.put(CLIENT_ATTR, "demo-http-client");
    }

    @Override
    public void onEnd(
        AttributesBuilder attributes,
        Context context,
        Object request,
        Object response,
        Throwable error) {}
  }

  /** Custom attributes extractor that adds demo-specific attributes. */
  private static class DemoAttributesExtractor implements AttributesExtractor<Object, Object> {
    private static final AttributeKey<String> CUSTOM_ATTR = AttributeKey.stringKey("demo.custom");
    private static final AttributeKey<String> ERROR_ATTR = AttributeKey.stringKey("demo.error");

    @Override
    public void onStart(AttributesBuilder attributes, Context context, Object request) {
      attributes.put(CUSTOM_ATTR, "demo-extension");
    }

    @Override
    public void onEnd(
        AttributesBuilder attributes,
        Context context,
        Object request,
        Object response,
        Throwable error) {
      if (error != null) {
        attributes.put(ERROR_ATTR, error.getClass().getSimpleName());
      }
    }
  }

  /** Custom metrics that track request counts. */
  private static class DemoMetrics implements OperationMetrics {
    @Override
    public OperationListener create(Meter meter) {
      LongCounter requestCounter =
          meter
              .counterBuilder("demo.requests")
              .setDescription("Number of requests")
              .setUnit("requests")
              .build();

      return new OperationListener() {
        @Override
        public Context onStart(Context context, Attributes attributes, long startNanos) {
          requestCounter.add(1, attributes);
          return context;
        }

        @Override
        public void onEnd(Context context, Attributes attributes, long endNanos) {
          // Could add duration metrics here if needed
        }
      };
    }
  }

  /** Context customizer that adds request correlation IDs and custom context data. */
  private static class DemoContextCustomizer implements ContextCustomizer<Object> {
    private static final AtomicLong requestIdCounter = new AtomicLong(1);
    private static final ContextKey<String> REQUEST_ID_KEY = ContextKey.named("demo.request.id");

    @Override
    public Context onStart(Context context, Object request, Attributes startAttributes) {
      // Generate a unique request ID for correlation
      String requestId = "req-" + requestIdCounter.getAndIncrement();

      // Add custom context data that can be accessed throughout the request lifecycle
      context = context.with(REQUEST_ID_KEY, requestId);
      return context;
    }
  }
}

@AutoService(ConfigurablePropagatorProvider.class)
public class DemoPropagatorProvider implements ConfigurablePropagatorProvider {
  @Override
  public TextMapPropagator getPropagator(ConfigProperties config) {
    return new DemoPropagator();
  }

  @Override
  public String getName() {
    return "demo";
  }
}

@AutoService(ConfigurableSamplerProvider.class)
public class DemoConfigurableSamplerProvider implements ConfigurableSamplerProvider {

  @Override
  public Sampler createSampler(ConfigProperties config) {
    return new DemoSampler();
  }

  @Override
  public String getName() {
    return "demo";
  }
}

@AutoService(ResourceProvider.class)
public class DemoResourceProvider implements ResourceProvider {
  @Override
  public Resource createResource(ConfigProperties config) {
    Attributes attributes = Attributes.builder().put("custom.resource", "demo").build();
    return Resource.create(attributes);
  }
}