tty.go

package main

import (
	"fmt"
	"os"
	"runtime"
	"syscall"
	"unsafe"
)

// isTerminal reports if the given file descriptor is attached to a terminal.
// • On Linux it calls ioctl(TCGETS).
// • On all other OSes it always returns false since colors are only implemented for Linux
func isTerminal(fd uintptr) bool {
	if runtime.GOOS != "linux" {
		return false // avoid platform-specific hassles
	}

	const ioctlReadTermios = 0x5401 // TCGETS on Linux

	var termios syscall.Termios
	_, _, err := syscall.Syscall6(
		syscall.SYS_IOCTL,
		fd,
		uintptr(ioctlReadTermios),
		uintptr(unsafe.Pointer(&termios)),
		0, 0, 0,
	)
	return err == 0
}

// printColoredPrefix writes an ANSI escape sequence to set the color.
func printColoredPrefix(color string) {
	fmt.Fprintf(os.Stderr, "\033[%sm", color)
}

// printColoredSuffix resets the terminal color.
func printColoredSuffix() {
	fmt.Fprint(os.Stderr, "\033[0m")
}

// FprintfError writes an error message to stderr. If stderr is a TTY,
// it prints the message in bright red.
func FprintfError(format string, args ...interface{}) {
	if isTerminal(os.Stderr.Fd()) {
		printColoredPrefix("1;31") // bright red
		fmt.Fprintf(os.Stderr, format, args...)
		printColoredSuffix()
	} else {
		// If it's not a terminal, just print normally (no colors).
		fmt.Fprintf(os.Stderr, format, args...)
	}
}