package bunrouterotel

import (
	"net/http"
	"strings"

	"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    = "0.5.0"
)

var tracer = otel.Tracer(tracerName, trace.WithInstrumentationVersion("semver:"+version))

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
	})
}

func getForwardedFor(r *http.Request) []string {
	h := r.Header.Get("X-Forwarded-For")
	a := strings.Split(h, ",")
	for i, s := range a {
		a[i] = strings.Trim(s, " \t")
	}
	return a
}

// 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()
	}
	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 == "" {
				if req.Request != nil && req.Request.URL != nil && req.Request.URL.Path != "" {
					route = req.Request.URL.Path
				} else {
					route = "route not found"
				}
			}
			spanName = req.Method + " " + route
			tracerStartOpts := []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, tracerStartOpts...)
			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...)
			forwardedFor := getForwardedFor(req.Request)
			if forwardedFor != nil {
				span.SetAttributes(attribute.StringSlice("http.forward_route", forwardedFor))
			}
			defer span.End()
			return next(w, req)
		}
	}
}