{ pkgs, lib, config, ... }:
with lib; {
  options.mods.impermanence.enable = mkEnableOption "enables impermanence";

  config = mkIf config.mods.impermanence.enable {
    environment.persistence."/persist" = {
      directories = [ "/var/lib/nixos" "/var/lib/systemd/coredump" ];
      files = [ "/var/lib/sops-nix/key.txt" "/etc/machine-id" ];
    };

    boot.initrd.postResumeCommands = lib.mkAfter ''
      mkdir /btrfs_tmp
      mount /dev/mapper/crypted /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
    '';
  };
}
