Windows Golang / Caesar Cipher

Code

package main

import (
    "fmt"
    "os"
)

func cipher(text string, direction int) string {

        shift, offset := rune(3), rune(26)
	runes := []rune(text)

        for index, char := range runes {
		switch direction {
		case -1: // encoding
			if char >= 'a'+shift && char <= 'z' ||
				char >= 'A'+shift && char <= 'Z' {
				char = char - shift
			} else if char >= 'a' && char < 'a'+shift ||
				char >= 'A' && char < 'A'+shift {
				char = char - shift + offset
			}
		case +1: // decoding
			if char >= 'a' && char <= 'z'-shift ||
				char >= 'A' && char <= 'Z'-shift {
				char = char + shift
			} else if char > 'z'-shift && char <= 'z' ||
				char > 'Z'-shift && char <= 'Z' {
				char = char + shift - offset
			}
		}
		runes[index] = char
	}
	return string(runes)
}

func encode(text string) string { return cipher(text, -1) }
func decode(text string) string { return cipher(text, +1) }

func main() {
	sec := os.Args[1]
        fmt.Println("[+] Clear text: " + sec)
	encoded := encode(sec)
	fmt.Println("[+] Encoded: " + encoded)
	decoded := decode(encoded)
	fmt.Println("[+] Decoded: " + decoded)
}