//go:build linux

package main

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

func setRawMode(fd int) (func(), error) {
	if fd == 0 {
		fd = int(os.Stdin.Fd())
	}
	if !isTerminal(fd) {
		return func() {}, nil
	}
	var oldState syscall.Termios
	if _, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), syscall.TCGETS, uintptr(unsafe.Pointer(&oldState)), 0, 0, 0); err != 0 {
		return func() {}, fmt.Errorf("tcgets: %v", err)
	}
	newState := oldState
	newState.Iflag &^= syscall.IGNBRK | syscall.BRKINT | syscall.PARMRK | syscall.ISTRIP | syscall.INLCR | syscall.IGNCR | syscall.ICRNL | syscall.IXON
	newState.Oflag &^= syscall.OPOST
	newState.Lflag &^= syscall.ECHO | syscall.ECHONL | syscall.ICANON | syscall.ISIG | syscall.IEXTEN
	newState.Cflag &^= syscall.CSIZE | syscall.PARENB
	newState.Cflag |= syscall.CS8
	newState.Cc[syscall.VMIN] = 1
	newState.Cc[syscall.VTIME] = 0
	if _, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), syscall.TCSETS, uintptr(unsafe.Pointer(&newState)), 0, 0, 0); err != 0 {
		return func() {}, fmt.Errorf("tcset: %v", err)
	}
	return func() {
		syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), syscall.TCSETS, uintptr(unsafe.Pointer(&oldState)), 0, 0, 0)
	}, nil
}

func isTerminal(fd int) bool {
	var t syscall.Termios
	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), syscall.TCGETS, uintptr(unsafe.Pointer(&t)), 0, 0, 0)
	return err == 0
}