source = $$(printf '%s\n' '$(OPK_SOURCE)' | sed 's/[.].*//')
upstream_archive = $(source)-$(OPK_SOURCE_VERSION_UPSTREAM).tar.gz
upstream_url = http://ftp.gnu.org/pub/gnu/$(source)/$(upstream_archive)
source_archive = ../$(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).orig.tar.gz

gpg = GNUPGHOME=gnupghome/ gpg --no-default-keyring --keyring ../keyring.gpg
keys = \
	'7C01 35FB 088A AF6C 66C6  50B9 BB58 69F0 64EA 74AB'

$(source_archive):
	wget -c "$(upstream_url)" "$(upstream_url).sig"
	install -m 0700 -d gnupghome/
	[ -e ../keyring.gpg ] || \
		$(gpg) --keyserver hkp://pool.sks-keyservers.net \
			--recv-keys $(keys); \
	rm -f ../keyring.gpg~; \
	if ! $(gpg) --verify "$(upstream_archive).sig"; then \
		rm -Rf gnupghome/; \
		exit 1; \
	fi
	rm -Rf gnupghome/
	mv "$(upstream_archive)" '$(source_archive)'

source: $(source_archive)