// Copyright (C) 2016 Sebastian 'tokkee' Harl <sh@tokkee.org>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
// OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// server is the backend server implementation.
package main

import (
	"flag"
	"log"
	"net"
	"strconv"
	"strings"

	"golang.org/x/net/context"

	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/peer"

	pb "tokkee.org/go-talk/grpc/proto/backend"
)

var (
	listen = flag.String("listen", ":50051", "listening address")
)

// A server implements the Backend service.
type server struct{}

// Query runs the user-provided query and returns the result.
func (*server) Query(ctx context.Context, in *pb.QueryRequest) (*pb.QueryReply, error) {
	if peer, ok := peer.FromContext(ctx); ok {
		log.Printf("Query() called from %v", peer)
	} else {
		log.Print("No peer information available")
	}

	t, n, err := runQuery(in.Query)
	if err != nil {
		return nil, err
	}

	return &pb.QueryReply{
		Type: t,
		N:    n,
	}, nil
}

// runQuery executes a query. It implements a highly sophisticated query
// engine.
func runQuery(q string) (string, int64, error) {
	fields := strings.SplitN(q, " ", 2)
	if len(fields) != 2 {
		return "", 0, grpc.Errorf(codes.InvalidArgument, "invalid query %q: want <cmd> <arg>", q)
	}

	var n int64
	cmd, arg := strings.ToUpper(fields[0]), fields[1]
	switch cmd {
	case "COUNT":
		n = int64(len(arg))
	case "RANDOM":
		i, err := strconv.Atoi(arg)
		if err != nil {
			return "", 0, grpc.Errorf(codes.InvalidArgument, "RANDOM: %v", err)
		}

		// Chosen by fair dice roll.
		n = 4
		if i <= 4 {
			n = 0
		}
	default:
		return "", 0, grpc.Errorf(codes.InvalidArgument, "unknown query command %q", cmd)
	}

	return cmd, n, nil
}

func main() {
	flag.Parse()

	l, err := net.Listen("tcp", *listen)
	if err != nil {
		log.Fatalf("Failed to listen on %s: %v", *listen, err)
	}

	log.Printf("Listening on %s ...", *listen)
	s := grpc.NewServer()
	pb.RegisterBackendServer(s, &server{})
	s.Serve(l)
}