A Tour of Go Exercise: rot13Reader

exercise-rot-reader.go

package main

import (
	"fmt"
	"io"
	"os"
	"strings"
)

type rot13Reader struct {
	r io.Reader
}

type Rot13ReaderError struct {
	Why string
}

func (e Rot13ReaderError) Error() string {
	return e.Why
}

func rot13(s []byte) []byte {
	rotator := func(c, start byte) byte { return ((c - start + 13) % 26) + start }
	
	for i, c := range s {
		if c >= 'A' && c <= 'Z' {
			s[i] = rotator(c, 'A')
		} else if c >= 'a' && c <= 'z' {
			s[i] = rotator(c, 'a')
		}
	}
	return s
}

func (r13r *rot13Reader) Read(s []byte) (int, error) {
	n, err := r13r.r.Read(s)
	if err != nil {
		return 0, &Rot13ReaderError{fmt.Sprintf("Could not read the stream: %v", err)}
	}

	s = rot13(s)
	return n, nil
}

func main() {
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}