package tracing

import (
	"net/http"
	"time"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/codes"
	"go.opentelemetry.io/otel/propagation"
	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
	"go.opentelemetry.io/otel/trace"
)

// Transport wraps an http.RoundTripper with tracing.
type Transport struct {
	base http.RoundTripper
}

// NewTransport creates a new tracing transport wrapper.
func NewTransport(base http.RoundTripper) *Transport {
	if base == nil {
		base = http.DefaultTransport
	}
	return &Transport{base: base}
}

// RoundTrip implements http.RoundTripper with tracing.
func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
	ctx := req.Context()
	tracer := otel.Tracer(tracerName)
	propagator := otel.GetTextMapPropagator()

	// Start client span
	spanName := "HTTP " + req.Method + " " + req.URL.Host + req.URL.Path
	ctx, span := tracer.Start(ctx, spanName,
		trace.WithSpanKind(trace.SpanKindClient),
		trace.WithAttributes(
			semconv.HTTPRequestMethodKey.String(req.Method),
			semconv.URLFull(req.URL.String()),
			semconv.ServerAddress(req.URL.Host),
			attribute.String("upstream.name", req.URL.Host),
		),
	)
	defer span.End()

	// Inject trace context into outgoing request headers
	propagator.Inject(ctx, propagation.HeaderCarrier(req.Header))

	// Perform the request
	start := time.Now()
	resp, err := t.base.RoundTrip(req.WithContext(ctx))
	duration := time.Since(start)

	// Record timing
	span.SetAttributes(attribute.Float64("http.request.duration_ms", float64(duration.Milliseconds())))

	if err != nil {
		span.RecordError(err)
		span.SetStatus(codes.Error, err.Error())
		return nil, err
	}

	// Record response attributes
	span.SetAttributes(
		semconv.HTTPResponseStatusCode(resp.StatusCode),
	)

	if resp.StatusCode >= 400 {
		span.SetStatus(codes.Error, http.StatusText(resp.StatusCode))
	} else {
		span.SetStatus(codes.Ok, "")
	}

	return resp, nil
}