nix-config/modules/nixos/impermanence/default.nix

{
  config,
  lib,
  namespace,
  ...
}:
with lib;
let
  cfg = config.${namespace}.impermanence;
in
{
  imports = [ ./options.nix ];

  config = mkIf cfg.enable {
    security.sudo.extraConfig = ''
      # rollback results in sudo lectures after each reboot
      Defaults lecture = never
    '';

    system.activationScripts = {
      "var-lib-private-permissions" = {
        deps = [ "createPersistentStorageDirs" ];
        text = ''
          mkdir -p /var/lib/private
          chmod 0700 /var/lib/private
        '';
      };
    };

    boot.initrd.systemd.services.rootfs-cleanup = {
      description = "Clean file system root";
      wantedBy = [
        "initrd.target"
      ];
      after = [
        "initrd-root-device.target"
      ];
      before = [
        "sysroot.mount"
      ];
      unitConfig.DefaultDependencies = "no";
      serviceConfig.Type = "oneshot";
      script =
        if (hasAttr "/" config.fileSystems) && (config.fileSystems."/".fsType == "btrfs") then
          ''
            # workaround for machines without working rtc battery
            # The time may not yet be correctly set, so wait until it is
            if [[ $(date '+%s') -lt 1730469314 ]]; then
              sleep 30 # this should hopefully be enough
            fi
            mkdir /btrfs_tmp
            mount ${config.fileSystems."/".device} -t btrfs /btrfs_tmp
            if [[ -e /btrfs_tmp/root ]]; then
              mkdir -p /btrfs_tmp/old_roots
              timestamp=$(date --date="@$(stat -c %X /btrfs_tmp/root)" "+%Y-%m-%d_%H:%M:%S")
              mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$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" || rm -rf "$1"
            }

            for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -atime +30); do
              delete_subvolume_recursively "$i"
            done

            btrfs subvolume create /btrfs_tmp/root
            umount /btrfs_tmp
          ''
        else if (hasAttr "/" config.fileSystems) && (config.fileSystems."/".fsType == "bcachefs") then
          ''
            # workaround for machines without working rtc battery
            # The time may not yet be correctly set, so wait until it is
            if [[ $(date '+%s') -lt 1730469314 ]]; then
              sleep 30 # this should hopefully be enough
            fi
            if [[ -e /root_tmp/root ]]; then
              mkdir -p /root_tmp/old_roots
              timestamp=$(date --date="@$(stat -c %X /root_tmp/root)" "+%Y-%m-%d_%H:%M:%S")
              mv /root_tmp/root "/root_tmp/old_roots/$timestamp"
            fi

            for i in $(find /root_tmp/old_roots/ -maxdepth 1 -atime +30); do
              bcachefs subvolume delete $i
            done

            bcachefs subvolume create /root_tmp/root
          ''
        else
          # For tmpfs or other filesystems, do nothing
          "";
    };

    assertions = [
      {
        assertion = hasAttr "/" config.fileSystems;
        message = "To use impermanence, you need to define a root volume";
      }

      {
        assertion =
          if hasAttr "/" config.fileSystems then
            config.fileSystems."/".fsType == "btrfs" || config.fileSystems."/".fsType == "bcachefs" || config.fileSystems."/".fsType == "tmpfs"
          else
            false;
        message = "rootfs must be btrfs, bcachefs, or tmpfs; not " + config.fileSystems."/".fsType;
      }

      {
        assertion =
          if hasAttr "/" config.fileSystems && (config.fileSystems."/".fsType == "btrfs" || config.fileSystems."/".fsType == "bcachefs") then
            any (
              t: t == "subvol=root" || t == "subvol=/root" || t == "X-mount.subdir=subvolumes/root"
            ) config.fileSystems."/".options
          else
            true;
        message = "btrfs or bcachefs rootfs must mount subvolume root";
      }
      {
        assertion = !config.boot.isContainer;
        message = "impermanence is not supported in containers";
      }
    ];

    environment.persistence.${cfg.persistencePath} = {
      hideMounts = true;
      directories = [
        "/var/lib/bluetooth"
        "/var/lib/iwd"
        "/var/lib/nixos"
        "/var/lib/libvirt"
        "/var/lib/waydroid"
        "/var/lib/systemd/coredump"
        "/etc/NetworkManager/system-connections"
        "/var/lib/tailscale"
        "/var/lib/homeassistant"
        "/var/lib/mosquitto"
        "/var/lib/music-assistant"
        "/var/lib/postgresql"
        "/var/lib/zigbee2mqtt"
        {
          directory = "/var/lib/colord";
          user = "colord";
          group = "colord";
          mode = "u=rwx,g=rx,o=";
        }
        {
          directory = "/etc/nix";
          user = "root";
          group = "root";
          mode = "u=rwx,g=rx,o=rx";
        }
        {
          directory = "/var/lib/private/authentik/media";
          user = "authentik";
          group = "authentik";
          mode = "u=rwx,g=,o=";
        }
        {
          directory = "/var/lib/private";
          mode = "u=rwx,g=rx,o=";
        }
        {
          directory = "/media/nas";
          user = "nas-apps";
          group = "jallen-nas";
          mode = "u=rwx,g=rx,o=rx";
        }
        {
          directory = "/var/lib/crowdsec";
          user = "crowdsec";
          group = "crowdsec";
          mode = "u=rwx,g=rwx,o=rx";
        }
        {
          directory = "/plugins-storage";
          user = "traefik";
          group = "traefik";
          mode = "u=rwx,g=rwx,o=rx";
        }
      ];
      files = [
        "/etc/machine-id"
      ];
    };
  };
}