Morse code
It has been in use for more than 175 years — longer than any other electronic encoding system.



Task

Send a string as audible Morse code to an audio device   (e.g., the PC speaker).



As the standard Morse code does not contain all possible characters,
you may either ignore unknown characters in the file,
or indicate them somehow   (e.g. with a different pitch).




// Command morse translates an input string into morse code,
// showing the output on the console, and playing it as sound.
// Only works on ubuntu.
package main
 
import (
	"flag"
	"fmt"
	"log"
	"regexp"
	"strings"
	"syscall"
	"time"
	"unicode"
)
 
// A key represents an action on the morse key.
// It's either on or off, for the given duration.
type key struct {
	duration int
	on       bool
	sym      string // for debug output
}
 
var (
	runeToKeys   = map[rune][]key{}
	interCharGap = []key{{1, false, ""}}
	punctGap     = []key{{7, false, " / "}}
	charGap      = []key{{3, false, " "}}
	wordGap      = []key{{7, false, " / "}}
)
 
const rawMorse = `
A:.-    J:.---  S:...    1:.----  .:.-.-.-  ::---...
B:-...  K:-.-   T:-      2:..---  ,:--..--  ;:-.-.-.
C:-.-.  L:.-..  U:..-    3:...--  ?:..--..  =:-...-
D:-..   M:--    V:...-   4:....-  ':.----.  +:.-.-.
E:.     N:-.    W:.--    5:.....  !:-.-.--  -:-....-
F:..-.  O:---   X:-..-   6:-....  /:-..-.   _:..--.-
G:--.   P:.--.  Y:-.--   7:--...  (:-.--.   ":.-..-.
H:....  Q:--.-  Z:--..   8:---..  ):-.--.-  $:...-..-
I:..    R:.-.   0:-----  9:----.  &:.-...   @:.--.-.
`
 
func init() {
	// Convert the rawMorse table into a map of morse key actions.
	r := regexp.MustCompile("([^ ]):([.-]+)")
	for _, m := range r.FindAllStringSubmatch(rawMorse, -1) {
		c := m[1][0]
		keys := []key{}
		for i, dd := range m[2] {
			if i > 0 {
				keys = append(keys, interCharGap...)
			}
			if dd == '.' {
				keys = append(keys, key{1, true, "."})
			} else if dd == '-' {
				keys = append(keys, key{3, true, "-"})
			} else {
				log.Fatalf("found %c in morse for %c", dd, c)
			}
			runeToKeys[rune(c)] = keys
			runeToKeys[unicode.ToLower(rune(c))] = keys
		}
	}
}
 
// MorseKeys translates an input string into a series of keys.
func MorseKeys(in string) ([]key, error) {
	afterWord := false
	afterChar := false
	result := []key{}
	for _, c := range in {
		if unicode.IsSpace(c) {
			afterWord = true
			continue
		}
		morse, ok := runeToKeys[c]
		if !ok {
			return nil, fmt.Errorf("can't translate %c to morse", c)
		}
		if unicode.IsPunct(c) && afterChar {
			result = append(result, punctGap...)
		} else if afterWord {
			result = append(result, wordGap...)
		} else if afterChar {
			result = append(result, charGap...)
		}
		result = append(result, morse...)
		afterChar = true
		afterWord = false
	}
	return result, nil
}
 
func main() {
	var ditDuration time.Duration
	flag.DurationVar(&ditDuration, "d", 40*time.Millisecond, "length of dit")
	flag.Parse()
	in := "hello world."
	if len(flag.Args()) > 1 {
		in = strings.Join(flag.Args(), " ")
	}
	keys, err := MorseKeys(in)
	if err != nil {
		log.Fatalf("failed to translate: %s", err)
	}
	for _, k := range keys {
		if k.on {
			if err := note(true); err != nil {
				log.Fatalf("failed to play note: %s", err)
			}
		}
		fmt.Print(k.sym)
		time.Sleep(ditDuration * time.Duration(k.duration))
		if k.on {
			if err := note(false); err != nil {
				log.Fatalf("failed to stop note: %s", err)
			}
		}
	}
	fmt.Println()
}
 
// Implement sound on ubuntu. Needs permission to access /dev/console.
 
var consoleFD uintptr
 
func init() {
	fd, err := syscall.Open("/dev/console", syscall.O_WRONLY, 0)
	if err != nil {
		log.Fatalf("failed to get console device: %s", err)
	}
	consoleFD = uintptr(fd)
}
 
const KIOCSOUND = 0x4B2F
const clockTickRate = 1193180
const freqHz = 600
 
// note either starts or stops a note.
func note(on bool) error {
	arg := uintptr(0)
	if on {
		arg = clockTickRate / freqHz
	}
	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, consoleFD, KIOCSOUND, arg)
	if errno != 0 {
		return errno
	}
	return nil
 
}
 