package tracing

import (
	"context"

	"github.com/go-kratos/kratos/v2/middleware"
	"github.com/go-kratos/kratos/v2/transport/grpc"
	"github.com/go-kratos/kratos/v2/transport/http"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/trace"
	"google.golang.org/grpc/metadata"
)

// Option is tracing option.
type Option func(*options)

type options struct {
	TracerProvider trace.TracerProvider
	Propagators    propagation.TextMapPropagator
}

func WithPropagators(propagators propagation.TextMapPropagator) Option {
	return func(opts *options) {
		opts.Propagators = propagators
	}
}

func WithTracerProvider(provider trace.TracerProvider) Option {
	return func(opts *options) {
		opts.TracerProvider = provider
	}
}

// Server returns a new server middleware for OpenTelemetry.
func Server(opts ...Option) middleware.Middleware {
	tracer := NewTracer(trace.SpanKindServer, opts...)

	return func(handler middleware.Handler) middleware.Handler {
		return func(ctx context.Context, req interface{}) (reply interface{}, err error) {
			var (
				component string
				operation string
				carrier   propagation.TextMapCarrier
			)
			if info, ok := http.FromServerContext(ctx); ok {
				// HTTP span
				component = "HTTP"
				operation = info.Request.RequestURI
				carrier = propagation.HeaderCarrier(info.Request.Header)
				ctx = otel.GetTextMapPropagator().Extract(ctx, propagation.HeaderCarrier(info.Request.Header))
			} else if info, ok := grpc.FromServerContext(ctx); ok {
				// gRPC span
				component = "gRPC"
				operation = info.FullMethod
				if md, ok := metadata.FromIncomingContext(ctx); ok {
					carrier = MetadataCarrier(md)
				}
			}
			ctx, span := tracer.Start(ctx, component, operation, carrier)
			defer tracer.End(ctx, span, err)

			reply, err = handler(ctx, req)

			return
		}
	}
}

// Client returns a new client middleware for OpenTelemetry.
func Client(opts ...Option) middleware.Middleware {
	tracer := NewTracer(trace.SpanKindClient, opts...)

	return func(handler middleware.Handler) middleware.Handler {
		return func(ctx context.Context, req interface{}) (reply interface{}, err error) {
			var (
				component string
				operation string
				carrier   propagation.TextMapCarrier
			)
			if info, ok := http.FromClientContext(ctx); ok {
				// HTTP span
				component = "HTTP"
				operation = info.Request.RequestURI
				carrier = propagation.HeaderCarrier(info.Request.Header)
			} else if info, ok := grpc.FromClientContext(ctx); ok {
				// gRPC span
				component = "gRPC"
				operation = info.FullMethod
				md, ok := metadata.FromOutgoingContext(ctx)
				if !ok {
					md = metadata.Pairs()
				}
				carrier = MetadataCarrier(md)
				ctx = metadata.NewOutgoingContext(ctx, md)
			}
			ctx, span := tracer.Start(ctx, component, operation, carrier)
			defer tracer.End(ctx, span, err)

			reply, err = handler(ctx, req)

			return
		}
	}
}