package main

import (
	"time"

	"golang.org/x/net/context"

	"github.com/go-kit/kit/addsvc/pb"
	"github.com/go-kit/kit/addsvc/reqrep"
	"github.com/go-kit/kit/endpoint"
	"github.com/go-kit/kit/metrics"
)

// A binding wraps an Endpoint so that it's usable by a transport. grpcBinding
// makes an Endpoint usable over gRPC.
type grpcBinding struct{ endpoint.Endpoint }

// Add implements the proto3 AddServer by forwarding to the wrapped Endpoint.
//
// As far as I can tell, gRPC doesn't (currently) provide a user-accessible
// way to manipulate the RPC context, like headers for HTTP. So we don't have
// a way to transport e.g. Zipkin IDs with the request. TODO.
func (b grpcBinding) Add(ctx context.Context, req *pb.AddRequest) (*pb.AddReply, error) {
	r, err := b.Endpoint(ctx, reqrep.AddRequest{A: req.A, B: req.B})
	if err != nil {
		return nil, err
	}

	resp, ok := r.(reqrep.AddResponse)
	if !ok {
		println("### 2")
		return nil, endpoint.ErrBadCast
	}

	return &pb.AddReply{V: resp.V}, nil
}

func grpcInstrument(requests metrics.Counter, duration metrics.Histogram) func(pb.AddServer) pb.AddServer {
	return func(next pb.AddServer) pb.AddServer {
		return grpcInstrumented{requests, duration, next}
	}
}

type grpcInstrumented struct {
	requests metrics.Counter
	duration metrics.Histogram
	next     pb.AddServer
}

func (i grpcInstrumented) Add(ctx context.Context, req *pb.AddRequest) (*pb.AddReply, error) {
	i.requests.Add(1)
	defer func(begin time.Time) { i.duration.Observe(time.Since(begin).Nanoseconds()) }(time.Now())
	return i.next.Add(ctx, req)
}