import (
 // "bufio"
 "flag"
 "fmt"
 "io"
 "os"
)
import "strconv"
var infile *string = flag.String("f", "Null", "please input a file name or dir.")
var size *string = flag.String("s", "0", "please input a dst file size.")
//func dataCopy(file *os.File, file *os.File)
func SplitFile(file *os.File, size int) {
 finfo, err := file.Stat()
 if err != nil {
  fmt.Println("get file info failed:", file, size)
 }
 fmt.Println(finfo, size)
 //每次最多拷貝1m
 bufsize := 1024 * 1024
 if size < bufsize {
  bufsize = size
 }
 buf := make([]byte, bufsize)
 num := (int(finfo.Size()) + size - 1) / size
 fmt.Println(num, len(buf))
 for i := 0; i < num; i++ {
  copylen := 0
  newfilename := finfo.Name() + strconv.Itoa(i)
  newfile, err1 := os.Create(newfilename)
  if err1 != nil {
   fmt.Println("failed to create file", newfilename)
  } else {
   fmt.Println("create file:", newfilename)
  }
  for copylen < size {
   n, err2 := file.Read(buf)
   if err2 != nil && err2 != io.EOF {
    fmt.Println(err2, "failed to read from:", file)
    break
   }
   if n <= 0 {
    break
   }
   //fmt.Println(n, len(buf))
   //寫文件
   w_buf := buf[:n]
   newfile.Write(w_buf)
   copylen += n
  }
 }
 return
}
func main() {
 flag.Parse()
 if *infile == "Null" {
  fmt.Println("no file to input")
  return
 }
 file, err := os.Open(*infile)
 if err != nil {
  fmt.Println("failed to open:", *infile)
 }
 defer file.Close()
 size, _ := strconv.Atoi(*size)
 SplitFile(file, size*1024)
}