package main

import (
	"errors"
	"fmt"
	"unicode/utf8"
)

func main() {
  input := "The quick brown fox jumped over the lazy dog"
  rev, revErr := Reverse(input)
  doubleRev, doubleRevErr := Reverse(rev)
  fmt.Printf("original: %q\n", input)
  fmt.Printf("reversed: %q, err: %v\n", rev, revErr)
  fmt.Printf("reversed again: %q, err: %v\n", doubleRev, doubleRevErr)

}

/* Bug causing code. Invalidates multibyte-characters. Kanji, etc.
func Reverse(s string) string {
  b := []byte(s)
  for i,j := 0, len(b) - 1; i < len(b)/2; i, j = i+1, j-1 {
    b[i], b[j] = b[j], b[i]
  }
  return string(b)
}
*/

/* also causes bug. when the input string is set to rune, that
encodes the byte slice as UTF-8, replacing the original character
func Reverse(s string) string {
  r := []rune(s)
  for i,j := 0, len(r) - 1; i < len(r) /2; i,j = i+1, j-1{
    r[i], r[j] = r[j], r[i]
  }
  return string(r)
}
*/

func Reverse(s string) (string, error) {
  if !utf8.ValidString(s) {
    return s, errors.New("input is not valid UTF-8")
  }
  fmt.Printf("input: %q\n",s)
  r:=[]rune(s)
  fmt.Printf("runes: %q\n", r)
  for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
    r[i], r[j] = r[j], r[i]
  }
  return string(r), nil
}