package main

import (
	"bytes"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"

	"golang.org/x/sys/unix"
	"golang.org/x/term"
)

func main() {
	st, err := term.MakeRaw(0)
	if err != nil {
		os.Exit(1)
	}

	var column int
	select {
	case <-time.After(100 * time.Millisecond):
	case column = <-awaitColumn():
	}

	term.Restore(0, st)
	if column > 1 {
		unix.Write(1, []byte("🚫\n")) // U+1F6AB
	}
}

func awaitColumn() <-chan int {
	ch := make(chan int)
	go func() {
		row, col := readDSR()
		_ = row
		ch <- col
	}()
	return ch
}

func readDSR() (row, col int) {
	unix.Write(1, []byte{
		'\033', '[', // ANSI escape code: CSI
		'6', 'n', // DSR / device status report
	})

	buf := make([]byte, 64)
	n, err := unix.Read(0, buf)
	if err != nil {
		return 0, 0
	}
	buf = buf[:n]

	if len(buf) < 6 || buf[0] != '\033' || buf[1] != '[' || buf[len(buf)-1] != 'R' {
		return 0, 0
	}

	s := string(buf[2 : len(buf)-1])
	pos := strings.IndexByte(s, ';')
	if pos == -1 {
		return 0, 0
	}

	row, err = strconv.Atoi(s[:pos])
	if err != nil {
		return 0, 0
	}
	col, err = strconv.Atoi(s[pos+1:])
	if err != nil {
		return 0, 0
	}
	return row, col
}

func processit(b []byte) {
	if !bytes.HasPrefix(b, []byte{'\033', '['}) {
		return
	}
	if !bytes.HasSuffix(b, []byte{'R'}) {
		return
	}
	s := string(b[2 : len(b)-1])
	pos := strings.IndexByte(s, ';')
	if pos == -1 {
		return
	}
	x, err := strconv.Atoi(s[pos+1:])
	if err != nil {
		return
	}
	if x != 1 {
		fmt.Println("🚫") // U+1F6AB
	}
}

func readit() chan []byte {
	q := make(chan []byte)
	go func() {
		b := make([]byte, 1024)
		n, _ := os.Stdin.Read(b)
		q <- b[:n]
	}()
	return q
}