package main

import (
	"bufio"
	"fmt"
	"golang.org/x/term"
	"os"
)

func isAscii(char rune) bool {
	ord := int(char)

	return ord < 0x80
}

func isCtrl(char rune) bool {
	if !isAscii(char) {
		return false
	}

	ord := int(char)

	return ord == 0x7f || ord < 0x20
}

// Return the input code of a Ctrl-key chord.
func ctrlKey(char rune) rune {
	ord := int(char)
	raw := ord & 0x1f

	if !isCtrl(rune(raw)) {
		return 0
	}

	return rune(raw)
}

// Put the terminal in raw mode
func rawOn() *term.State {
	oldState, err := term.MakeRaw(int(os.Stdin.Fd()))
	if err != nil {
		panic(err)
	}

	return oldState
}

// Restore the terminal to canonical mode
func rawOff(oldState *term.State) {
	err := term.Restore(int(os.Stdin.Fd()), oldState)
	if err != nil {
		panic(err)
	}
}

// Print a formatted string to stdout, with CRLF line endings for proper terminal formatting
func outLn(format string, a ...interface{}) {
	formatted := fmt.Sprintf(format, a...)

	fmt.Printf("%s\r\n", formatted)
}

func main() {
	// Go to proper raw mode, but restore canonical mode at extit
	oldState := rawOn()
	defer rawOff(oldState)

	reader := bufio.NewReader(os.Stdin)

	for {
		char, _, err := reader.ReadRune()
		if err != nil {
			panic(err)
		}

		// Ugliest syntax structure ever?
		switch {
		case char == ctrlKey('q'):
			outLn("bye!")
			return
		case isCtrl(char):
			outLn("%d", char)
		default:
			outLn("%d ('%c')", char, char)
		}
	}
}