package telemetry

import (
	"context"
	"net"
	"testing"
	"time"

	"go.opentelemetry.io/otel"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	semconv "go.opentelemetry.io/otel/semconv/v1.24.0"
)

// fakeCollector starts a TCP listener that accepts connections but speaks no protocol.
// Returns the address and a cleanup function.
func fakeCollector(t *testing.T) string {
	t.Helper()
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("fakeCollector: %v", err)
	}
	t.Cleanup(func() { ln.Close() })
	// Accept in background so gRPC dial doesn't get refused.
	go func() {
		for {
			conn, err := ln.Accept()
			if err != nil {
				return
			}
			conn.Close()
		}
	}()
	return ln.Addr().String()
}

func cfgWith(endpoint string) Config {
	return Config{
		ServiceName:    "test-service",
		ServiceVersion: "0.0.1",
		Environment:    "test",
		OTLPEndpoint:   endpoint,
		OTLPInsecure:   true,
	}
}

func TestNew_ShutdownCallable(t *testing.T) {
	endpoint := fakeCollector(t)
	ctx := context.Background()

	shutdown, err := New(ctx, cfgWith(endpoint))
	if err != nil {
		t.Fatalf("New: %v", err)
	}
	if shutdown == nil {
		t.Fatal("shutdown func is nil")
	}
	// Use a short timeout: the fake server doesn't speak gRPC so flush will fail,
	// but we only care that shutdown is callable and returns (not that export succeeds).
	shutCtx, cancel := context.WithTimeout(ctx, 200*time.Millisecond)
	defer cancel()
	_ = shutdown(shutCtx) // export errors with fake server are expected
}

func TestNew_SetsGlobalTracerProvider(t *testing.T) {
	endpoint := fakeCollector(t)
	ctx := context.Background()

	shutdown, err := New(ctx, cfgWith(endpoint))
	if err != nil {
		t.Fatalf("New: %v", err)
	}
	t.Cleanup(func() {
		shutCtx, cancel := context.WithTimeout(ctx, 200*time.Millisecond)
		defer cancel()
		_ = shutdown(shutCtx)
	})

	tp := otel.GetTracerProvider()
	if _, ok := tp.(*sdktrace.TracerProvider); !ok {
		t.Errorf("expected *sdktrace.TracerProvider, got %T", tp)
	}
}

func TestNew_SetsGlobalMeterProvider(t *testing.T) {
	endpoint := fakeCollector(t)
	ctx := context.Background()

	shutdown, err := New(ctx, cfgWith(endpoint))
	if err != nil {
		t.Fatalf("New: %v", err)
	}
	t.Cleanup(func() {
		shutCtx, cancel := context.WithTimeout(ctx, 200*time.Millisecond)
		defer cancel()
		_ = shutdown(shutCtx)
	})

	mp := otel.GetMeterProvider()
	if _, ok := mp.(*sdkmetric.MeterProvider); !ok {
		t.Errorf("expected *sdkmetric.MeterProvider, got %T", mp)
	}
}

func TestNewResource_Fields(t *testing.T) {
	cfg := Config{
		ServiceName:    "my-service",
		ServiceVersion: "2.0.0",
		Environment:    "staging",
	}
	res := newResource(cfg)

	check := func(key, want string) {
		t.Helper()
		for _, kv := range res.Attributes() {
			if string(kv.Key) == key {
				if got := kv.Value.AsString(); got != want {
					t.Errorf("resource[%s]: want %q, got %q", key, want, got)
				}
				return
			}
		}
		t.Errorf("resource attribute %q not found", key)
	}

	check(string(semconv.ServiceNameKey), "my-service")
	check(string(semconv.ServiceVersionKey), "2.0.0")
	check("deployment.environment", "staging")
}

func TestNewResource_MergesWithDefault(t *testing.T) {
	cfg := Config{ServiceName: "svc"}
	res := newResource(cfg)
	if res == nil {
		t.Fatal("newResource returned nil")
	}
	// Default resource contributes service.instance.id and telemetry.sdk.* fields.
	if len(res.Attributes()) == 0 {
		t.Error("resource has no attributes")
	}
}

func TestNewResource_IsNotDefault(t *testing.T) {
	cfg := Config{ServiceName: "unique-service-name"}
	res := newResource(cfg)
	def := resource.Default()
	// Custom resource must differ from the bare default: it has extra attributes.
	if len(res.Attributes()) <= len(def.Attributes()) {
		t.Error("newResource added no attributes beyond the default")
	}
}