/*
 *
 * Copyright 2024 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net"
	"net/http"

	"google.golang.org/grpc"
	pb "google.golang.org/grpc/examples/features/proto/echo"
	"google.golang.org/grpc/stats/opentelemetry"

	"github.com/prometheus/client_golang/prometheus/promhttp"
	"go.opentelemetry.io/otel/exporters/prometheus"
	"go.opentelemetry.io/otel/sdk/metric"
)

var (
	addr               = flag.String("addr", ":50051", "the server address to connect to")
	prometheusEndpoint = flag.String("prometheus_endpoint", ":9464", "the Prometheus exporter endpoint")
)

type echoServer struct {
	pb.UnimplementedEchoServer
	addr string
}

func (s *echoServer) UnaryEcho(ctx context.Context, req *pb.EchoRequest) (*pb.EchoResponse, error) {
	return &pb.EchoResponse{Message: fmt.Sprintf("%s (from %s)", req.Message, s.addr)}, nil
}

func main() {
	exporter, err := prometheus.New()
	if err != nil {
		log.Fatalf("Failed to start prometheus exporter: %v", err)
	}
	provider := metric.NewMeterProvider(metric.WithReader(exporter))
	go http.ListenAndServe(*prometheusEndpoint, promhttp.Handler())

	so := opentelemetry.ServerOption(opentelemetry.Options{MetricsOptions: opentelemetry.MetricsOptions{MeterProvider: provider}})

	lis, err := net.Listen("tcp", *addr)
	if err != nil {
		log.Fatalf("Failed to listen: %v", err)
	}
	s := grpc.NewServer(so)
	pb.RegisterEchoServer(s, &echoServer{addr: *addr})

	log.Printf("Serving on %s\n", *addr)

	if err := s.Serve(lis); err != nil {
		log.Fatalf("Failed to serve: %v", err)
	}
}
