/**
 * Created by IntelliJ IDEA.
 * User: Ar.M
 * Date: 2020-05-10
 * Time: 22:13
 */
package main

import (
	"fmt"
	"google.golang.org/grpc"
	"io"
	"log"
	"net"
	"os"
	"path/filepath"
	"runtime"
	transportpb "yunlian-file-transfer-demo/proto"
)

var filesDir string

func init() {
	_, fp, _, ok := runtime.Caller(0)
	if !ok {
		log.Fatalf("Get caller failed")
	}
	filesDir = filepath.Join(filepath.Dir(fp), "files")
}

type server struct{}

func (s *server) Download(req *transportpb.FileRequest, stream transportpb.FileService_DownloadServer) error {
	fileName := req.GetFileName()
	fileRange := req.GetFileRange()

	path := filepath.Join(filesDir, fileName)

	fileInfo, err := os.Stat(path)
	if err != nil {
		return err
	}
	fileSize := fileInfo.Size()

	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	if fileRange > 0 {
		_, err = f.Seek(fileRange, 0)
		if err != nil {
			return err
		}
		log.Printf("read file at seek: %d\n", fileRange)
	}

	var totalBytesStreamed int64

	for totalBytesStreamed < fileSize {
		block := make([]byte, 1024)
		bytesRead, err := f.Read(block)
		if err == io.EOF {
			break
		}

		if err != nil {
			return err
		}

		if err := stream.Send(&transportpb.FileResponse{
			Block:    block,
			FileSize: fileSize,
		}); err != nil {
			return err
		}
		totalBytesStreamed += int64(bytesRead)
	}
	return nil
}

func main() {
	lis, err := net.Listen("tcp", "0.0.0.0:10086")
	if err != nil {
		log.Fatalf("Failed to listen on 10086 : %v\n", err)
	}

	s := grpc.NewServer()
	transportpb.RegisterFileServiceServer(s, &server{})

	fmt.Println("Starting server on 10086")
	if err := s.Serve(lis); err != nil {
		log.Fatalf("failed to start server : %v\n", err)
	}
}