package tracing

// todo, review:
// https://github.com/ttys3/tracing-go/blob/main/tracing.go#L136

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"os"

	"go.ntppool.org/common/logger"
	"go.ntppool.org/common/version"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/sdk/resource"
	otelsdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.24.0"
	"go.opentelemetry.io/otel/trace"
)

// https://github.com/open-telemetry/opentelemetry-go/blob/main/exporters/otlp/otlptrace/otlptracehttp/example_test.go

type TpShutdownFunc func(ctx context.Context) error

func Tracer() trace.Tracer {
	traceProvider := otel.GetTracerProvider()
	return traceProvider.Tracer("ntppool-tracer")
}

func Start(ctx context.Context, spanName string, opts ...trace.SpanStartOption) (context.Context, trace.Span) {
	return Tracer().Start(ctx, spanName, opts...)
}

type GetClientCertificate func(*tls.CertificateRequestInfo) (*tls.Certificate, error)

type TracerConfig struct {
	ServiceName string
	Environment string
	Endpoint    string
	EndpointURL string

	CertificateProvider GetClientCertificate
	RootCAs             *x509.CertPool
}

var emptyTpShutdownFunc = func(_ context.Context) error {
	return nil
}

func InitTracer(ctx context.Context, cfg *TracerConfig) (TpShutdownFunc, error) {

	log := logger.Setup()

	// exporter, err := srv.newStdoutExporter(os.Stdout)

	var err error
	var exporter otelsdktrace.SpanExporter

	if otlpEndPoint := os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"); len(otlpEndPoint) > 0 || len(cfg.Endpoint) > 0 {
		exporter, err = newOLTPExporter(ctx, cfg)
	}

	if err != nil {
		return emptyTpShutdownFunc, err
	}

	if exporter == nil {
		log.Warn("tracing not configured")
		return emptyTpShutdownFunc, nil
	}

	resource, err := newResource(cfg)
	if err != nil {
		return nil, err
	}

	tp := otelsdktrace.NewTracerProvider(
		otelsdktrace.WithSampler(otelsdktrace.AlwaysSample()),
		otelsdktrace.WithBatcher(exporter),
		otelsdktrace.WithResource(resource),
	)

	otel.SetTracerProvider(tp)

	otel.SetTextMapPropagator(
		propagation.NewCompositeTextMapPropagator(
			propagation.TraceContext{}, // W3C Trace Context format; https://www.w3.org/TR/trace-context/
			propagation.Baggage{},
		),
	)

	return tp.Shutdown, nil
}

func newOLTPExporter(ctx context.Context, cfg *TracerConfig) (otelsdktrace.SpanExporter, error) {

	log := logger.Setup()

	opts := []otlptracehttp.Option{
		otlptracehttp.WithCompression(otlptracehttp.GzipCompression),
	}

	if cfg.CertificateProvider != nil {
		log.InfoContext(ctx, "setting up cert provider")
		opts = append(opts, otlptracehttp.WithTLSClientConfig(&tls.Config{
			GetClientCertificate: cfg.CertificateProvider,
			RootCAs:              cfg.RootCAs,
		}))
	}

	if len(cfg.Endpoint) > 0 {
		opts = append(opts, otlptracehttp.WithEndpoint(cfg.Endpoint))
	}

	if len(cfg.EndpointURL) > 0 {
		opts = append(opts, otlptracehttp.WithEndpointURL(cfg.EndpointURL))
	}

	client := otlptracehttp.NewClient(opts...)
	exporter, err := otlptrace.New(ctx, client)
	if err != nil {
		log.ErrorContext(ctx, "creating OTLP trace exporter", "err", err)
	}
	return exporter, err
}

// func (srv *Server) newStdoutExporter(w io.Writer) (sdktrace.SpanExporter, error) {
// 	return stdouttrace.New(
// 		stdouttrace.WithWriter(w),
// 		// Use human-readable output.
// 		stdouttrace.WithPrettyPrint(),
// 		// Do not print timestamps for the demo.
// 		stdouttrace.WithoutTimestamps(),
// 	)
// }

// newResource returns a resource describing this application.
func newResource(cfg *TracerConfig) (*resource.Resource, error) {

	log := logger.Setup()

	defaultResource := resource.Default()
	log.Debug("default semconv", "url", defaultResource.SchemaURL())

	newResource := resource.NewWithAttributes(
		semconv.SchemaURL,
		semconv.ServiceNameKey.String(cfg.ServiceName),
		semconv.ServiceVersionKey.String(version.Version()),
		attribute.String("environment", cfg.Environment),
	)

	log.Debug("new resource semconv", "url", newResource.SchemaURL())

	r, err := resource.Merge(
		defaultResource,
		newResource,
	)
	if err != nil {
		log.Error("could not setup otel resource",
			"err", err,
			"default", defaultResource.SchemaURL(),
			"local", newResource.SchemaURL(),
		)
	}

	return r, nil
}