// > go run .

2024/08/12 20:45:09 running @ localhost:8000
2024/08/12 20:45:32 simulating a call to external api
2024/08/12 20:45:38 simulating a call to external api
2024/08/12 20:45:42 simulating a call to external api
2024/08/12 20:45:47 simulating a call to external api

// > watch -n 2 curl -s localhost:8000/rolldice
Every 2.0s: curl -s localhost:8000/rolldice

4

## TODO: find out what is slow

_Assuming we didn't already know_ :)

- [ ] Add more logs
- [ ] Add metrics (response time, number of calls, etc)

*OR*

- [x] Add OTel

// main.go
	import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"

	// Set up OpenTelemetry.
	otelShutdown, err := setupOTelSDK(ctx)
	if err != nil {
		return
	}
	// Handle shutdown properly so nothing leaks.
	defer func() {
		err = errors.Join(err, otelShutdown(context.Background()))
	}()
    
    ...
    
    handleFunc := func(pattern string, handlerFunc func(http.ResponseWriter, *http.Request)) {
	// Configure the "http.route" for the HTTP instrumentation.
	handler := otelhttp.WithRouteTag(pattern, http.HandlerFunc(handlerFunc))
	mux.Handle(pattern, handler)

    handler := otelhttp.NewHandler(mux, "/")

// otel.go

func setupOTelSDK(ctx context.Context) (shutdown func(context.Context) error, err error) {

	// Set up trace provider.
	tracerProvider, err := newTraceProvider()
	if err != nil {
		handleErr(err)
		return
	}
	shutdownFuncs = append(shutdownFuncs, tracerProvider.Shutdown)
	otel.SetTracerProvider(tracerProvider)
    
    case "stdout":
	  exporter, err = stdouttrace.New(
        stdouttrace.WithPrettyPrint()
      )

// rolldice.go
var (
	tracer  = otel.Tracer("rolldice")
	meter   = otel.Meter("rolldice")
	rollCnt metric.Int64Counter
)

func rolldice(w http.ResponseWriter, r *http.Request) {
	ctx, span := tracer.Start(r.Context(), "rolling dice")
	defer span.End()

	roll := 1 + rand.Intn(6)

	// Sleep for a few seconds, so we can see longer traces
	// And breakout the slow api call versus other work
	// that might be done in this function, i.e. a DB query
	time.Sleep(time.Millisecond * time.Duration(roll*100))

	span.AddEvent("simulating a call to external api")
	err := simulateSlowAPI(500*roll, ctx)
	if err != nil {
		log.Printf("Failed to make call to external api")
	}

	rollValueAttr := attribute.Int("roll.value", roll)
	span.SetAttributes(rollValueAttr)
	rollCnt.Add(ctx, 1, metric.WithAttributes(rollValueAttr))

// rolldice.go

func simulateSlowAPI(sleepInMilliseconds int, ctx context.Context) error {
	ctx, childSpan := tracer.Start(ctx, "simulatedSlowApiSpan")
	defer childSpan.End()
	// Construct the URL with the sleep parameter
	baseURL := "https://fakeresponder.com/"
	sleepParam := "?sleep=" + strconv.Itoa(sleepInMilliseconds)

// ✗ go run .

{"Resource":[
  {"Key":"service.name","Value":
   {"Type":"STRING","Value":"dice"}
  },
  {"Key":"service.version","Value":
   {"Type":"STRING","Value":"0.1.0"}
  },
  {"Key":"telemetry.sdk.language","Value":
   {"Type":"STRING","Value":"go"}
  },
  {"Key":"telemetry.sdk.name","Value":
   {"Type":"STRING","Value":"opentelemetry"}
  },
  {"Key":"telemetry.sdk.version","Value":
   {"Type":"STRING","Value":"1.25.0"}
  }
],"ScopeMetrics":[]}

{"Resource":[{"Key":"service.name","Value":{"Type":"STRING","Value":"dice"}},{"Key":"service.version","Value":{"Type":"STRING","Value":"0.1.0"}},{"Key":"telemetry.sdk.language","Value":{"Type":"STRING","Value":"go"}},{"Key":"telemetry.sdk.name","Value":{"Type":"STRING","Value":"opentelemetry"}},{"Key":"telemetry.sdk.version","Value":{"Type":"STRING","Value":"1.25.0"}}],"ScopeMetrics":[]}

{
	"Name": "/",
	"SpanContext": {
		"TraceID": "5a844fd338c4c00ec001fb28ea352c64",
		"SpanID": "4908426582a52298",
	},
	"Parent": {
		"TraceID": "00000000000000000000000000000000",
		"SpanID": "0000000000000000",
	},
	"SpanKind": 2,
	"StartTime": "2024-04-25T00:21:00.179788-06:00",
	"EndTime": "2024-04-25T00:21:01.471713625-06:00",
	"Attributes": [
		{
			"Key": "http.route",
			"Value": {
				"Type": "STRING",
				"Value": "/rolldice"
			}
		},

{
	"Name": "rolling dice",
	"SpanContext": {
		"TraceID": "5a844fd338c4c00ec001fb28ea352c64",
		"SpanID": "7e394450317027c5",
	},
	"Parent": {
		"TraceID": "5a844fd338c4c00ec001fb28ea352c64",
		"SpanID": "4908426582a52298",
	},
    "Attributes": [
		{
			"Key": "roll.value",
			"Value": {
				"Type": "INT64",
				"Value": 2
			}
		}
	],

> docker run -d --name jaeger \
  -e COLLECTOR_OTLP_ENABLED=true \
  -p 16686:16686 \
  -p 4317:4317 \
  -p 4318:4318 \
  jaegertracing/all-in-one:latest
  

> OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 go run .

// otel.go

func createOtelExporter(exporterType string) (trace.SpanExporter, error) {

    case "otlp":
		var opts []otlptracehttp.Option
	
		exporter, err = otlptrace.New(
			context.Background(),
			otlptracehttp.NewClient(opts...),
		)
	case "stdout":
		exporter, err = stdouttrace.New(stdouttrace.WithPrettyPrint())

// rolldice.go

// A function for simulating slowness with an external http call
func simulateSlowAPI(sleepInMilliseconds int, ctx context.Context) error {
	_, childSpan := tracer.Start(ctx, "simulatedSlowApiSpan")
	defer childSpan.End()
	// Construct the URL with the sleep parameter
	baseURL := "https://fakeresponder.com/"
	sleepParam := "?sleep=" + strconv.Itoa(sleepInMilliseconds)

	// Create the full URL
	fullURL := baseURL + sleepParam

	// Make the GET request
	childSpan.AddEvent("GET fakeresponder.com api")
	resp, err := http.Get(fullURL)