//go:build linux

package serial

import (
	"fmt"

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

func platformModemLinkState(entry MappingChannel) LinkState {
	if entry.LinkSignal == "unknown" {
		return LinkState{Channel: entry.Channel, State: "unknown", Signal: "unknown", Message: "physical modem link signal is not board-validated"}
	}
	fd, err := unix.Open(entry.Device, unix.O_RDWR|unix.O_NOCTTY|unix.O_NONBLOCK|unix.O_CLOEXEC, 0)
	if err != nil {
		return LinkState{Channel: entry.Channel, State: "unknown", Signal: "unknown", Message: "serial device cannot be opened for modem status"}
	}
	defer unix.Close(fd)
	bits, err := unix.IoctlGetInt(fd, unix.TIOCMGET)
	if err != nil {
		return LinkState{Channel: entry.Channel, State: "unknown", Signal: "unknown", Message: fmt.Sprintf("%s modem status is unavailable", entry.LinkSignal)}
	}
	var mask int
	switch entry.LinkSignal {
	case "dcd":
		mask = unix.TIOCM_CAR
	case "dsr":
		mask = unix.TIOCM_DSR
	case "cts":
		mask = unix.TIOCM_CTS
	default:
		return LinkState{Channel: entry.Channel, State: "unknown", Signal: "unknown", Message: "unsupported modem link signal"}
	}
	state := "down"
	if bits&mask != 0 {
		state = "up"
	}
	return LinkState{Channel: entry.Channel, State: state, Signal: entry.LinkSignal, Available: true}
}