morse.go

// morse.go
// usage:
// go run morse.go "SOS" > sos.au

package main

import (
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"math"
	"os"
)

var MorseCode = map[string]string{
	"A": ".-",
	"B": "-...",
	"C": "-.-.",
	"D": "-..",
	"E": ".",
	"F": "..-.",
	"G": "--.",
	"H": "....",
	"I": "..",
	"J": ".---",
	"K": "-.-",
	"L": ".-..",
	"M": "--",
	"N": "-.",
	"O": "---",
	"P": ".--.",
	"Q": "--.-",
	"R": ".-.",
	"S": "...",
	"T": "-",
	"U": "..--",
	"V": "...-",
	"W": ".--",
	"X": "-..-",
	"Y": "-.--",
	"Z": "--..",
	"0": "-----",
	"1": ".----",
	"2": "..---",
	"3": "...--",
	"4": "....-",
	"5": ".....",
	"6": "-....",
	"7": "--...",
	"8": "---..",
	"9": "----.",
}

type au struct {
	file       io.Writer
	sampleRate int
	gain       float64
}

func (a *au) writeHeader() {
	var offset, size, format, rate, channels uint32
	magic := [4]byte{'.', 's', 'n', 'd'}
	offset = 24
	size = 0xffffffff
	format = 2
	rate = uint32(a.sampleRate)
	channels = 1

	if err := binary.Write(a.file, binary.BigEndian, magic); err != nil {
		log.Fatalf("%v", err)
	}
	if err := binary.Write(a.file, binary.BigEndian, offset); err != nil {
		log.Fatalf("%v", err)
	}
	if err := binary.Write(a.file, binary.BigEndian, size); err != nil {
		log.Fatalf("%v", err)
	}
	if err := binary.Write(a.file, binary.BigEndian, format); err != nil {
		log.Fatalf("%v", err)
	}
	if err := binary.Write(a.file, binary.BigEndian, rate); err != nil {
		log.Fatalf("%v", err)
	}
	if err := binary.Write(a.file, binary.BigEndian, channels); err != nil {
		log.Fatalf("%v", err)
	}
}

func (a *au) beep(seconds, freq float64) {
	samples := float64(a.sampleRate) * seconds
	for i := 0; i < int(samples); i++ {
		var t float64
		var value int8
		t = float64(i) / float64(a.sampleRate)
		value = int8(math.Sin(t*2*math.Pi*freq) * 128 * a.gain)
		if err := binary.Write(a.file, binary.BigEndian, value); err != nil {
			log.Fatalf("%v", err)
		}
	}
}

func (a *au) silence(seconds float64) {
	samples := float64(a.sampleRate) * seconds
	for i := 0; i < int(samples); i++ {
		var value float64
		if err := binary.Write(a.file, binary.BigEndian, value); err != nil {
			log.Fatalf("%v", err)
		}
	}
}

func (a *au) writeString(message string) {
	for _, s := range message {
		c, ok := MorseCode[string(s)]
		if !ok {
			a.silence(0.7)
			continue
		}
		for _, x := range c {
			switch x {
			case 46:
				fmt.Printf(".\n")
				a.beep(0.2, 1000)
			case 45:
				fmt.Printf("_\n")
				a.beep(0.6, 1000)
			}
			a.silence(0.1)
		}
	}
}

func main() {
	a := &au{os.Stdout, 8000, 0.4}
	a.writeHeader()
	a.writeString(os.Args[1])
}