package obsx

import (
	"context"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/sdk/resource"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
	"go.opentelemetry.io/otel/trace"
)

// TracerConfig configures the OpenTelemetry tracer.
type TracerConfig struct {
	ServiceName    string
	ServiceVersion string
	Endpoint       string  // OTLP gRPC endpoint, e.g. "localhost:4317"
	Sampler        float64 // sampling ratio, default: 1.0 (sample everything)
}

func (c *TracerConfig) defaults() {
	if c.Sampler <= 0 {
		c.Sampler = 1.0
	}
}

// SetupTracer initializes an OpenTelemetry tracer provider with OTLP gRPC exporter.
// Returns a shutdown function that must be called on application exit.
func SetupTracer(ctx context.Context, cfg TracerConfig) (shutdown func(context.Context) error, err error) {
	cfg.defaults()

	exporter, err := otlptracegrpc.New(ctx,
		otlptracegrpc.WithEndpoint(cfg.Endpoint),
		otlptracegrpc.WithInsecure(),
	)
	if err != nil {
		return nil, err
	}

	attrs := []resource.Option{
		resource.WithAttributes(semconv.ServiceName(cfg.ServiceName)),
	}
	if cfg.ServiceVersion != "" {
		attrs = append(attrs, resource.WithAttributes(semconv.ServiceVersion(cfg.ServiceVersion)))
	}

	res, err := resource.New(ctx, attrs...)
	if err != nil {
		return nil, err
	}

	tp := sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(exporter),
		sdktrace.WithResource(res),
		sdktrace.WithSampler(sdktrace.TraceIDRatioBased(cfg.Sampler)),
	)

	otel.SetTracerProvider(tp)

	return tp.Shutdown, nil
}

// StartSpan starts a new span using the global tracer provider.
func StartSpan(ctx context.Context, name string, opts ...trace.SpanStartOption) (context.Context, trace.Span) {
	return otel.Tracer("obsx").Start(ctx, name, opts...)
}