local/bin/homeinit: Run guix pull automatically

.local/bin/homeinit

@@ -1,7 +1,5 @@
 #!/bin/sh
 
-# TODO: Run guix pull if OPT_UPDATE and if guix chekout is more than some days old, as specified by an environment variable.
-
 # TODO: Guix pull on commit specified in package-lists/guix-version?
 # TODO: On foreign distro, use local package manager to install Guix.  (Start with pacman.)
 # TODO: Make functions to make it easier to re-order calls?
@@ -158,6 +156,35 @@ popd
 
 section "System packages"
 if inpath guix; then
+	if [ ! -e ~/.cache/guix/pull ]; then
+		message "Update Guix to yesterday's version"
+		git clone https://git.savannah.gnu.org/git/guix.git /tmp/guix
+		YESTERDAY_COMMIT=$(git -C /tmp/guix log --until=yesterday -n 1 --format=%H)
+		guix pull --commit=$YESTERDAY_COMMIT
+		unset YESTERDAY_COMMIT
+		rm -rv /tmp/guix
+	elif $OPT_UPDATE
+		CURRENT_COMMIT=$(guix --version 2>/dev/null | awk '{print $4; exit}')
+		REPO=$HOME/.cache/guix/pull/"$(ls -1 ~/.cache/guix/pull)"
+		CURRENT_COMMIT_DATE=git -C "$REPO" log -n 1 --format=%ct $CURRENT_COMMIT
+		git -C $REPO pull
+		LATEST_COMMIT_DATE=git -C "$REPO" log -n 1 --format=%ct
+
+		[ -z "$GUIX_DISTRO_AGE_WARNING" ] && GUIX_DISTRO_AGE_WARNING=$((7 * 24 * 60 * 60))
+
+		if [ $(($LATEST_COMMIT_DATE - $CURRENT_COMMIT)) -gt $GUIX_DISTRO_AGE_WARNING ]; then
+			message "Update Guix since it's older than a week."
+			YESTERDAY_COMMIT=$(git -C "$REPO" log --until=yesterday -n 1 --format=%H)
+			guix pull --commit=$YESTERDAY_COMMIT
+			unset YESTERDAY_COMMIT
+		fi
+		unset LATEST_COMMIT_DATE
+		unset CURRENT_COMMIT_DATE
+		unset REPO
+		unset CURRENT_COMMIT
+	fi
+
+
 	## TODO: The manifest will uninstall other unspecified packages.  Is this
 	## really what we want?
 	export GUIX_PACKAGE_PATH=$HOME/.guix-packages