Maple Go style

go get \
  go.opentelemetry.io/otel \
  go.opentelemetry.io/otel/sdk \
  go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp \
  go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp \
  go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp \
  go.opentelemetry.io/otel/log \
  go.opentelemetry.io/otel/sdk/log

package telemetry

import (
	"context"
	"os"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp"
	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
	"go.opentelemetry.io/otel/log/global"
	sdklog "go.opentelemetry.io/otel/sdk/log"
	"go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	"go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.24.0"
)

const (
	mapleEndpoint = "ingest.maple.dev" // EU: ingest.eu.maple.dev
	mapleKey      = "MAPLE_TEST" // public ingest key (maple_pk_…), or MAPLE_TEST until the user has one
)

func Init(ctx context.Context) (shutdown func(context.Context) error, err error) {
	headers := map[string]string{"authorization": "Bearer " + mapleKey}

	res, err := resource.New(ctx,
		resource.WithAttributes(
			semconv.ServiceName("orders-api"),
			semconv.DeploymentEnvironment(envOr("DEPLOYMENT_ENV", "development")),
			attribute.String("vcs.repository.url.full", "https://github.com/acme/orders-api"),
			attribute.String("vcs.ref.head.revision", envOr("GITHUB_SHA", envOr("GIT_COMMIT", ""))),
		),
	)
	if err != nil {
		return nil, err
	}

	traceExp, err := otlptracehttp.New(ctx,
		otlptracehttp.WithEndpoint(mapleEndpoint),
		otlptracehttp.WithHeaders(headers),
	)
	if err != nil {
		return nil, err
	}
	tp := trace.NewTracerProvider(trace.WithBatcher(traceExp), trace.WithResource(res))
	otel.SetTracerProvider(tp)

	logExp, err := otlploghttp.New(ctx,
		otlploghttp.WithEndpoint(mapleEndpoint),
		otlploghttp.WithHeaders(headers),
	)
	if err != nil {
		return nil, err
	}
	lp := sdklog.NewLoggerProvider(
		sdklog.WithProcessor(sdklog.NewBatchProcessor(logExp)),
		sdklog.WithResource(res),
	)
	global.SetLoggerProvider(lp)

	metricExp, err := otlpmetrichttp.New(ctx,
		otlpmetrichttp.WithEndpoint(mapleEndpoint),
		otlpmetrichttp.WithHeaders(headers),
	)
	if err != nil {
		return nil, err
	}
	mp := metric.NewMeterProvider(
		metric.WithReader(metric.NewPeriodicReader(metricExp)),
		metric.WithResource(res),
	)
	otel.SetMeterProvider(mp)

	return func(ctx context.Context) error {
		_ = tp.Shutdown(ctx)
		_ = lp.Shutdown(ctx)
		return mp.Shutdown(ctx)
	}, nil
}

func envOr(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}

func main() {
	ctx := context.Background()
	shutdown, err := telemetry.Init(ctx)
	if err != nil {
		log.Fatal(err)
	}
	defer shutdown(ctx)

	// app start
}

var tracer = otel.Tracer("orders.api")

func SubmitOrder(ctx context.Context, orderID string) (err error) {
	ctx, span := tracer.Start(ctx, "order.submit")
	defer func() {
		if err != nil {
			span.RecordError(err)
			span.SetStatus(codes.Error, err.Error())
		}
		span.End()
	}()

	span.SetAttributes(attribute.String("order.id", orderID))
	return chargeOrder(ctx, orderID)
}