dnl Check for LIBUSB compiler flags. On success, set nut_have_libusb="yes"
dnl and set LIBUSB_CFLAGS and LIBUSB_LDFLAGS. On failure, set
dnl nut_have_libusb="no". This macro can be run multiple times, but will
dnl do the checking only once.

AC_DEFUN([NUT_CHECK_LIBUSB],
[
if test -z "${nut_have_libusb_seen}"; then
	nut_have_libusb_seen=yes

	dnl save CFLAGS and LDFLAGS
	CFLAGS_ORIG="${CFLAGS}"
	LDFLAGS_ORIG="${LDFLAGS}"

	AC_MSG_CHECKING(for libusb version via pkg-config)
	LIBUSB_VERSION=`pkg-config --silence-errors --modversion libusb`
	if test "$?" = "0"; then
		AC_MSG_RESULT(${LIBUSB_VERSION} found)
		CFLAGS="`pkg-config --silence-errors --cflags libusb`"
		LDFLAGS="`pkg-config --silence-errors --libs libusb`"
	else
		AC_MSG_CHECKING(via libusb-config)
		LIBUSB_VERSION=`libusb-config --version 2>/dev/null`
		if test "$?" = "0"; then
			AC_MSG_RESULT(${LIBUSB_VERSION} found)
			CFLAGS="`libusb-config --cflags 2>/dev/null`"
			LDFLAGS="`libusb-config --libs 2>/dev/null`"
		else
			AC_MSG_RESULT(not found)
			CFLAGS=""
			LDFLAGS="-lusb"
		fi
	fi

	AC_MSG_CHECKING(for libusb cflags)
	AC_ARG_WITH(usb-includes, [
		AC_HELP_STRING([--with-usb-includes=CFLAGS], [include flags for the libusb library])
	], [CFLAGS="${withval}"], [])
	AC_MSG_RESULT([${CFLAGS}])

	AC_MSG_CHECKING(for libusb ldflags)
	AC_ARG_WITH(usb-libs, [
		AC_HELP_STRING([--with-usb-libs=LDFLAGS], [linker flags for the libusb library])
	], [LDFLAGS="${withval}"], [])
	AC_MSG_RESULT([${LDFLAGS}])

	dnl check if libusb is usable
	AC_CHECK_HEADERS(usb.h, [nut_have_libusb=yes], [nut_have_libusb=no], [AC_INCLUDES_DEFAULT])
	AC_CHECK_FUNCS(usb_init, [], [nut_have_libusb=no])

	if test "${nut_have_libusb}" = "yes"; then
		dnl Check for libusb "force driver unbind" availability
		AC_CHECK_FUNCS(usb_detach_kernel_driver_np)
		LIBUSB_CFLAGS="${CFLAGS}"
		LIBUSB_LDFLAGS="${LDFLAGS}"
	fi

	dnl restore original CFLAGS and LDFLAGS
	CFLAGS="${CFLAGS_ORIG}"
	LDFLAGS="${LDFLAGS_ORIG}"
fi
])