obm() { a__overlay_bind_mount "${@}"; }
a__overlay_bind_mount() {
	local directory
	for directory in "dev" "dev/pts" "proc" "sys"; do
		if ! mount --bind "/${directory}" "overlay/mount/${directory}"; then
			sh_log_error "Unable to bind mount directory: ${directory}"
			return 1
		fi
	done
}

obu() { a__overlay_bind_unmount "${@}"; }
a__overlay_bind_unmount() {
	local directory
	for directory in "sys" "proc" "dev/pts" "dev"; do
		if ! umount --lazy "overlay/mount/${directory}"; then
			sh_log_error "Unable to bind unmount directory: ${directory}"
			return 1
		fi
	done
}

ocr() { a__overlay_command_root "${@}"; }
a__overlay_command_root() {
	chroot \
		"overlay/mount" "${@}"
}

ocu() { a__overlay_command_user "${@}"; }
a__overlay_command_user() {
	chroot \
		--userspec "1000:1000" \
		"overlay/mount" "${@}"
}

omm() { a__overlay_mirror_mount "${@}"; }
a__overlay_mirror_mount() {
	mount --make-rslave --rbind "/deb" "overlay/mount/deb"
}

omu() { a__overlay_mirror_unmount "${@}"; }
a__overlay_mirror_unmount() {
	umount --recursive "overlay/mount/deb"
}

orm() { a__overlay_root_mount "${@}"; }
a__overlay_root_mount() {
	local root="${1}"
	if [ -z "${root}" ]; then
		sh_log_error "No root target directory"
		return 1
	fi
	root="$(realpath "${root}")"
	if ! mkdir "overlay"; then
		sh_log_error "Unable to make overlay directory"
		return 2
	fi
	(
		if ! cd "overlay"; then
			sh_log_error "Unable to move into overlay directory"
			return 3
		fi
		local directory
		for directory in "lower" "upper" "work" "mount"; do
			if ! mkdir --parents "${directory}"; then
				sh_log_error "Unable to make directory: ${directory}"
				return 4
			fi
		done
		local file="${root}/filesystem.squashfs"
		if ! mount "${file}" "lower"; then
			sh_log_error "Unable to lower mount: ${file}"
			return 5
		fi
		if ! mount \
			-o "lowerdir=lower,upperdir=upper,workdir=work" \
			-t "overlay" \
			"overlay" "mount"; then
			sh_log_error "Unable to overlay mount"
			return 6
		fi
	)
}

ors() { a__overlay_root_squash "${@}"; }
a__overlay_root_squash() {
	local directory="${1}"
	local file
	local level="${2}"
	if [ -n "${directory}" ]; then
		if mkdir "${directory}"; then
			[ -n "${level}" ] || level="18"
			for file in "vmlinuz" "initrd.img"; do
				cp "overlay/mount/${file}" "${directory}"
			done
			mksquashfs \
				"overlay/mount" "${directory}/filesystem.squashfs" \
				-noappend \
				-comp "zstd" -Xcompression-level "${level}"
			chown --recursive 1000:1000 "${directory}"
		fi
	fi
}

oru() { a__overlay_root_unmount "${@}"; }
a__overlay_root_unmount() {
	(
		if ! cd "overlay"; then
			sh_log_error "Unable to move into overlay directory"
			return 1
		fi
		if ! umount "mount"; then
			sh_log_error "Unable to unmount mount directory"
			return 2
		fi
		if ! rmdir "mount"; then
			sh_log_error "Unable to remove mount directory"
			return 3
		fi
		local directory
		for directory in "upper" "work"; do
			if ! rm --force --recursive "${directory}"; then
				sh_log_error "Unable to remove directory: ${directory}"
				return 4
			fi
		done
		if ! umount "lower"; then
			sh_log_error "Unable to unmount lower directory"
			return 5
		fi
		if ! rmdir "lower"; then
			sh_log_error "Unable to remove lower directory"
			return 6
		fi
	)
	if ! rmdir "overlay"; then
		sh_log_error "Unable to remove overlay directory"
		return 7
	fi
}