Add basic tracing to randomizer.App

We can see what the operation was, at least, which is interesting.

Author: featherbread

internal/randomizer/app.go

@@ -3,8 +3,13 @@ package randomizer
 import (
 	"context"
 	"math/rand/v2"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
 )
 
+var tracer = otel.Tracer("github.com/featherbread/randomizer/internal/randomizer")
+
 // Store enables persistence for named groups of options.
 type Store interface {
 	// List returns the names of all available groups. If no groups have been
@@ -50,10 +55,16 @@ func shuffle(options []string) {
 // All errors returned from Main are of type [Error], and support
 // [Error.HelpText] for user-friendly formatting.
 func (a App) Main(ctx context.Context, args []string) (Result, error) {
+	ctx, span := tracer.Start(ctx, "Main")
+	defer span.End()
+
 	request, err := a.newRequest(ctx, args)
 	if err != nil {
+		span.RecordError(err)
 		return Result{}, err
 	}
+
+	span.SetAttributes(attribute.String("operation", request.Operation.String()))
 	handler := appHandlers[request.Operation]
 	return handler(a, request)
 }

internal/randomizer/request.go

@@ -16,6 +16,24 @@ const (
 	deleteGroup
 )
 
+func (op operation) String() string {
+	switch op {
+	case makeSelection:
+		return "select"
+	case showHelp:
+		return "help"
+	case listGroups:
+		return "list"
+	case showGroup:
+		return "show"
+	case saveGroup:
+		return "save"
+	case deleteGroup:
+		return "delete"
+	}
+	return ""
+}
+
 // request represents a single user request to a randomizer instance, created
 // from raw user input.
 type request struct {