package telemetry

import (
	"context"
	"errors"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/sdk/resource"
	"go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.30.0"
)

func InitTelemetry(ctx context.Context) (shutdown func(context.Context) error, err error) {
	var shutdownFuncs []func(context.Context) error

	// shutdown 会调用通过 shutdownFuncs 注册的清理函数。
	// 调用产生的错误会被合并。
	// 每个注册的清理函数将被调用一次。
	shutdown = func(ctx context.Context) error {
		var err error
		for _, fn := range shutdownFuncs {
			err = errors.Join(err, fn(ctx))
		}
		shutdownFuncs = nil
		return err
	}

	// handleErr 调用 shutdown 进行清理，并确保返回所有错误信息。
	handleErr := func(inErr error) {
		err = errors.Join(inErr, shutdown(ctx))
	}

	// 设置传播器
	prop := newPropagator()
	otel.SetTextMapPropagator(prop)

	// 设置 trace provider.
	tracerProvider, err := newJaegerTraceProvider(ctx)
	if err != nil {
		handleErr(err)
		return
	}
	shutdownFuncs = append(shutdownFuncs, tracerProvider.Shutdown)
	otel.SetTracerProvider(tracerProvider)

	return
}

func newPropagator() propagation.TextMapPropagator {
	return propagation.NewCompositeTextMapPropagator(
		propagation.TraceContext{},
		propagation.Baggage{},
	)
}

func newJaegerTraceProvider(ctx context.Context) (*trace.TracerProvider, error) {
	// 创建一个使用 HTTP 协议连接本机Jaeger的 Exporter
	res, err := resource.New(ctx,
		resource.WithFromEnv(),
		resource.WithTelemetrySDK(),
		resource.WithHost(),
		resource.WithAttributes(
			// 在可观测链路 OpenTelemetry 版后端显示的服务名称。
			semconv.ServiceNameKey.String("VPT"),
		),
	)
	if err != nil {
		return nil, err
	}
	traceClientHttp := otlptracehttp.NewClient(
		otlptracehttp.WithEndpointURL("https://oltp.jerryyan.top/v1/traces"))
	otlptracehttp.WithCompression(1)
	traceExp, err := otlptrace.New(ctx, traceClientHttp)
	bsp := trace.NewBatchSpanProcessor(traceExp)
	tracerProvider := trace.NewTracerProvider(
		trace.WithSampler(trace.AlwaysSample()),
		trace.WithResource(res),
		trace.WithSpanProcessor(bsp),
	)
	return tracerProvider, nil
}