package main

import (
	"bufio"
	"fmt"
	"io"
	"os/exec"
	"strings"
)

func main() {
	cmd := exec.Command("idevicesyslog")
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		panic(err)
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		panic(err)
	}
	err = cmd.Start()
	if err != nil {
		panic(err)
	}

	go copyOutput(stdout)
	go copyOutput(stderr)
	cmd.Wait()
}

func copyOutput(r io.Reader) {
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		fmt.Println(decodeSyslog(scanner.Text()))
	}
}

func decodeSyslog(line string) string { // this function handles all special encoded characters
	specialChar := strings.Contains(line, `\134`) // this \134
	if specialChar {
		line = strings.Replace(line, `\134`, "", -1)
	}
	kBackslash := byte(0x5c)
	kM := byte(0x4d)
	kDash := byte(0x2d)
	kCaret := byte(0x5e)

	// Mask for the UTF-8 digit range.
	kNum := byte(0x30)

	bytes := []byte(line)
	var out []byte
	for i := 0; i < len(bytes); {

		if (bytes[i] != kBackslash) || i > (len(bytes)-4) {
			out = append(out, bytes[i])
			i = i + 1
		} else {
			if (bytes[i+1] == kM) && (bytes[i+2] == kCaret) {
				out = append(out, (bytes[i+3]&byte(0x7f))+byte(0x40))
			} else if bytes[i+1] == kM && bytes[i+2] == kDash {
				out = append(out, bytes[i+3]|byte(0x80))
			} else if isDigit(bytes[i+1:i+3], kNum) {
				out = append(out, decodeOctal(bytes[i+1], bytes[i+2], bytes[i+3]))
			} else {
				out = append(out, bytes[0], bytes[1], bytes[2], bytes[3], bytes[4])
			}
			i = i + 4
		}
	}
	return string(out)
}

func isDigit(b []byte, kNum byte) bool {
	for _, v := range b {
		if (v & byte(0xf0)) != kNum {
			return false
		}
	}
	return true
}

func decodeOctal(x, y, z byte) byte {
	return (x&byte(0x3))<<byte(6) | (y&byte(0x7))<<byte(3) | z&byte(0x7)
}