package tracing

import (
	"net/http"

	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/trace"
	"k8s.io/client-go/transport"
)

// RestConfigWrapper returns a rest.Config.Wrap-compatible wrapper that adds
// a client span to every Kubernetes API request already running inside a
// trace. Requests with no parent span pass through untouched: informer
// list/watch long-polls, leader-election renewals, and metrics authn would
// otherwise each become meaningless (and in the watch case, minutes-long)
// root spans. client-go applies Wrap innermost, so the span sees the final
// authenticated request.
func RestConfigWrapper(opts ...Option) transport.WrapperFunc {
	o := newOptions(opts)
	return func(rt http.RoundTripper) http.RoundTripper {
		otelOpts := []otelhttp.Option{
			// Explicit propagators: deterministic regardless of global
			// state. The apiserver ignores incoming traceparent (by
			// design), so injection is harmless there.
			otelhttp.WithPropagators(propagation.NewCompositeTextMapPropagator(
				propagation.TraceContext{}, propagation.Baggage{})),
		}
		if o.tp != nil {
			otelOpts = append(otelOpts, otelhttp.WithTracerProvider(o.tp))
		}
		return &parentGatedTransport{
			traced: otelhttp.NewTransport(rt, otelOpts...),
			plain:  rt,
		}
	}
}

// parentGatedTransport enforces the parent-span requirement itself rather
// than relying on otelhttp filter semantics for transports.
type parentGatedTransport struct {
	traced http.RoundTripper
	plain  http.RoundTripper
}

func (t *parentGatedTransport) RoundTrip(r *http.Request) (*http.Response, error) {
	if trace.SpanContextFromContext(r.Context()).IsValid() {
		return t.traced.RoundTrip(r)
	}
	return t.plain.RoundTrip(r)
}