TARGETS := $(shell { \
  if [ $$(date +%m) -lt 6 ]; then \
    echo "$$(date +%Y)0101.key $$(date +%Y)0601.key" ; \
  else \
    echo "$$(date +%Y)0601.key $$(($$(date +%Y) + 1))0101.key" ; \
  fi \
  })

all: $(TARGETS)

%.key:
	@set -eu ; \
	openssl genrsa -out "$@" 2048 ; \
	chgrp opendkim "$@" ; \
	chmod 0640 "$@" ; \
	echo ; \
	data="$$(printf "v=DKIM1; k=rsa; p=%s" \
	  "$$(openssl rsa -in "$@" -pubout -outform der 2>/dev/null | openssl base64 -A)")" ; \
	pos=0 ; \
	printf "%s._domainkey\tIN\tTXT\t" "$$(echo "$@" | cut -d. -f1)" ; \
	while true ; do \
	  printf "\"%s\"" \
	    "$$(echo "$$data" | cut -c $$((pos + 1))-$$((pos + 254)))" ; \
	  pos="$$((pos + 254))" ; \
	  [ $${#data} -gt $$pos ] || break ; \
	  printf " " ; \
	done ; \
	echo