package bunrouterotel

import (
	"net/http"

	"github.com/uptrace/bunrouter"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/propagation"
	semconv "go.opentelemetry.io/otel/semconv/v1.12.0"
	"go.opentelemetry.io/otel/trace"
)

const (
	tracerName = "git.blauwelle.com/go/crate/bunrouterotel"
	version    = "0.1.0"
)

type config struct {
	propagators propagation.TextMapPropagator
}

type Option interface {
	apply(cfg *config)
}

type optionFunc func(cfg *config)

func (o optionFunc) apply(cfg *config) {
	o(cfg)
}

func WithPropagators(propagators propagation.TextMapPropagator) Option {
	return optionFunc(func(cfg *config) {
		cfg.propagators = propagators
	})
}

// Middleware create a span, which record the request,
// HTTP status code is NOT recorded.
func Middleware(serverName string, opts ...Option) bunrouter.MiddlewareFunc {
	cfg := config{}
	for _, opt := range opts {
		opt.apply(&cfg)
	}
	if cfg.propagators == nil {
		cfg.propagators = otel.GetTextMapPropagator()
	}
	tracer := otel.Tracer(tracerName, trace.WithInstrumentationVersion("semver:"+version))
	return func(next bunrouter.HandlerFunc) bunrouter.HandlerFunc {
		return func(w http.ResponseWriter, req bunrouter.Request) error {
			ctx := cfg.propagators.Extract(req.Context(), propagation.HeaderCarrier(req.Header))
			var spanName string
			params := req.Params()
			route := params.Route()
			if route != "" {
				spanName = req.Method + " " + route
			} else {
				spanName = "HTTP " + req.Method + " route not found"
			}
			tarcerStartOpts := []trace.SpanStartOption{
				trace.WithAttributes(semconv.NetAttributesFromHTTPRequest("tcp", req.Request)...),
				trace.WithAttributes(semconv.EndUserAttributesFromHTTPRequest(req.Request)...),
				trace.WithAttributes(semconv.HTTPServerAttributesFromHTTPRequest(serverName, route, req.Request)...),
				trace.WithSpanKind(trace.SpanKindServer),
			}
			ctx, span := tracer.Start(ctx, spanName, tarcerStartOpts...)
			req.Request = req.Request.WithContext(ctx)
			paramSlice := params.Slice()
			attrs := make([]attribute.KeyValue, 0, len(paramSlice))
			for _, param := range paramSlice {
				attrs = append(attrs, attribute.String("http.route.param."+param.Key, param.Value))
			}
			span.SetAttributes(attrs...)
			defer span.End()
			return next(w, req)
		}
	}
}