//go:build linux

package serial

import (
	"io"

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

// pendingSerialInput prevents a blocking Read on WCH drivers that do not
// consistently honor O_NONBLOCK. TIOCINQ is an immediate queue-length query.
func pendingSerialInput(device io.ReadWriteCloser) (int, bool, error) {
	provider, ok := device.(interface{ Fd() uintptr })
	if !ok {
		return 0, false, nil
	}
	pending, err := unix.IoctlGetInt(int(provider.Fd()), unix.TIOCINQ)
	if err != nil {
		return 0, true, err
	}
	return pending, true, nil
}