enable impermanence for hopper

sys/machines/hopper/hardware.nix

@@ -1,4 +1,4 @@
-{config, ...}: {
+{lib, ...}: {
   nixpkgs.hostPlatform.system = "x86_64-linux";
 
   ## nvidia gpu
@@ -37,6 +37,31 @@
     };
   };
 
+  boot.initrd.postResumeCommands = lib.mkAfter ''
+    mkdir /btrfs_tmp
+    mount /dev/disk/by-uuid/1297e638-f2ff-49a2-a362-314ac7eeaabc /btrfs_tmp
+      if [[ -e /btrfs_tmp/root ]]; then
+        mkdir -p /btrfs_tmp/old_roots
+        timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/root)" "+%Y-%m-%-d_%H:%M:%S")
+        mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
+    fi
+
+    delete_subvolume_recursively() {
+        IFS=$'\n'
+        for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+            delete_subvolume_recursively "/btrfs_tmp/$i"
+        done
+        btrfs subvolume delete "$1"
+    }
+
+    for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
+        delete_subvolume_recursively "$i"
+    done
+
+    btrfs subvolume create /btrfs_tmp/root
+    umount /btrfs_tmp
+  '';
+
   fileSystems = {
     "/" = {
       device = "/dev/disk/by-uuid/1297e638-f2ff-49a2-a362-314ac7eeaabc";
@@ -53,6 +78,12 @@
       fsType = "btrfs";
       options = ["subvol=nix" "compress=zstd" "noatime"];
     };
+    "/persist" = {
+      device = "/dev/disk/by-uuid/1297e638-f2ff-49a2-a362-314ac7eeaabc";
+      neededForBoot = true;
+      fsType = "btrfs";
+      options = ["subvol=persist" "compress=zstd"];
+    };
     "/boot" = {
       device = "/dev/disk/by-uuid/8D4C-2F05";
       fsType = "vfat";