Modularize code

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/configs/persist/default.nix

@@ -0,0 +1,22 @@
+{ inputs, lib, ... }:
+
+{
+  imports = [ inputs.impermanence.nixosModules.impermanence ];
+
+  fileSystems."/persist".neededForBoot = true;
+  boot.initrd.postDeviceCommands = lib.mkAfter (builtins.readFile ./impermanence.sh);
+
+  environment.persistence."/persist" = {
+    hideMounts = true;
+    directories = [
+      "/etc/nixos"
+      "/etc/NetworkManager/system-connections"
+      "/var/lib/nixos"
+      "/var/lib/systemd/coredump"
+      "/var/log"
+    ];
+    files = [
+      "/etc/machine-id"
+    ];
+  };
+}

hosts/common/configs/persist/impermanence.sh

@@ -0,0 +1,25 @@
+delete_subvolume_recursively() {
+  IFS=$'\n'
+  for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+    delete_subvolume_recursively "/mnt/btrfs/$i"
+  done
+  btrfs subvolume delete "$1"
+}
+
+mkdir -p /mnt/btrfs
+mount /dev/mapper/luks /mnt/btrfs
+
+if [[ -e /mnt/btrfs/root ]]; then
+  mkdir -p /mnt/btrfs/root.bak
+  timestamp=$(date --date="@$(stat -c %Y /mnt/btrfs/root)" "+%Y-%m-%-d_%H:%M:%S")
+  mv /mnt/btrfs/root "/mnt/btrfs/root.bak/$timestamp"
+fi
+
+find /mnt/btrfs/root.bak/ -maxdepth 1 -mtime +14 | while IFS= read -r i; do
+  delete_subvolume_recursively "$i"
+done
+
+btrfs subvolume create /mnt/btrfs/root
+
+umount /mnt/btrfs
+rmdir /mnt/btrfs