package router

import (
	"context"
	"net/http"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/codes"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/trace"
)

// tracer is looked up per use rather than kept, so a provider installed after
// the router was built — as tests do — is the one spans go to.
func tracer() trace.Tracer { return otel.Tracer("gitea.mynodes.xyz/ilker/llmgw/internal/router") }

// startInference opens the span for one inference request, continuing the
// caller's trace when it sent a traceparent.
func startInference(req *http.Request, path, requestID string) (context.Context, trace.Span) {
	ctx := otel.GetTextMapPropagator().Extract(req.Context(), propagation.HeaderCarrier(req.Header))
	return tracer().Start(ctx, "inference "+path,
		trace.WithSpanKind(trace.SpanKindServer),
		trace.WithAttributes(
			attribute.String("llmgw.request_id", requestID),
			attribute.String("http.route", path),
		))
}

// endSpan closes a span, marking it failed when err is set.
func endSpan(span trace.Span, err error) {
	if err != nil {
		span.RecordError(err)
		span.SetStatus(codes.Error, err.Error())
	}
	span.End()
}

// withTraceparent is h with the current span's context in it, for the engine.
// A copy: the request's header is sent on every attempt, each its own span.
func withTraceparent(ctx context.Context, h http.Header) http.Header {
	if !trace.SpanContextFromContext(ctx).IsValid() {
		return h
	}
	out := h.Clone()
	if out == nil {
		out = http.Header{}
	}
	otel.GetTextMapPropagator().Inject(ctx, propagation.HeaderCarrier(out))
	return out
}