/*
 * Copyright (c) 2021 The Clymene 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 server

import (
	"fmt"
	"github.com/Clymene-project/Clymene/cmd/gateway/app/handler"
	"github.com/Clymene-project/Clymene/pkg/config/tlscfg"
	"github.com/Clymene-project/Clymene/prompb"
	"go.uber.org/zap"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
	"net"
)

// GRPCServerParams to construct a new Clymene Gateway gRPC Server
type GRPCServerParams struct {
	TLSConfig     tlscfg.Options
	HostPort      string
	MetricHandler *handler.GRPCMetricHandler
	Logger        *zap.Logger
	OnError       func(error)
}

// StartGRPCServer based on the given parameters
func StartGRPCServer(params *GRPCServerParams) (*grpc.Server, error) {
	var server *grpc.Server

	if params.TLSConfig.Enabled {
		// user requested a server with TLS, setup creds
		tlsCfg, err := params.TLSConfig.Config(params.Logger)
		if err != nil {
			return nil, err
		}

		creds := credentials.NewTLS(tlsCfg)
		server = grpc.NewServer(grpc.Creds(creds))
	} else {
		// server without TLS
		server = grpc.NewServer()
	}

	listener, err := net.Listen("tcp", params.HostPort)
	if err != nil {
		return nil, fmt.Errorf("failed to listen on gRPC port: %w", err)
	}

	if err := serveGRPC(server, listener, params); err != nil {
		return nil, err
	}

	return server, nil
}

func serveGRPC(server *grpc.Server, listener net.Listener, params *GRPCServerParams) error {
	prompb.RegisterClymeneServiceServer(server, params.MetricHandler)

	params.Logger.Info("Starting clymene-gateway gRPC server", zap.String("grpc.host-port", params.HostPort))
	go func() {
		if err := server.Serve(listener); err != nil {
			params.Logger.Error("Could not launch gRPC service", zap.Error(err))
			if params.OnError != nil {
				params.OnError(err)
			}
		}
	}()

	return nil
}
