# Generate/check/update a .h file to reflect the values of Makefile
# variables
#
# Example usage (by default, check-conf-h will consider all CFG_*
# variables):
#
# path/to/conf.h: FORCE
#	$(call check-conf-h)
#
# Or, to include only the variables with the given prefix(es):
#
# path/to/crypto_config.h: FORCE
#	$(call check-conf-h,CFG_CRYPTO_ CRYPTO_)

define check-conf-h
	$(q)set -e;						\
	echo '  CHK     $@';					\
	cnf="$(strip $(foreach var,				\
		$(call cfg-vars-by-prefix,$1),			\
		$(call cfg-make-define,$(var))))";		\
	guard="_`echo $@ | tr -- -/. ___`_";			\
	mkdir -p $(dir $@);					\
	echo "#ifndef $${guard}" >$@.tmp;			\
	echo "#define $${guard}" >>$@.tmp;			\
	echo -n "$${cnf}" | sed 's/_nl_ */\n/g' >>$@.tmp;	\
	echo "#endif" >>$@.tmp;					\
	if [ -r $@ ] && cmp -s $@ $@.tmp; then			\
		rm -f $@.tmp;					\
	else							\
		echo '  UPD     $@';				\
		mv $@.tmp $@;					\
	fi
endef

define cfg-vars-by-prefix
	$(strip $(if $(1),$(call _cfg-vars-by-prefix,$(1)),
			  $(call _cfg-vars-by-prefix,CFG_)))
endef

define _cfg-vars-by-prefix
	$(sort $(foreach prefix,$(1),$(filter $(prefix)%,$(.VARIABLES))))
endef

# Convert a makefile variable to a #define
# <undefined>, n => <undefined>
# y              => 1
# <other value>  => <other value>
define cfg-make-define
	$(strip $(if $(filter y,$($1)),
		     #define $1 1 /* '$($1)' */_nl_,
		     $(if $(filter xn x,x$($1)),
			  /* $1 is not set ('$($1)') */_nl_,
			  #define $1 $($1) /* '$($1)' */_nl_)))
endef