Nomarchy/core/system/impermanence.nix

{ config, lib, pkgs, inputs, ... }:

let
  cfg = config.nomarchy.system.impermanence;
in
{
  imports = [
    inputs.impermanence.nixosModules.impermanence
  ];

  options.nomarchy.system.impermanence = {
    enable = lib.mkEnableOption "Erase Your Darlings (Impermanence) root wipe on boot";

    # The disko layout names the main LUKS mapping `crypted` on single-disk
    # installs and `crypted_main` on multi-disk installs (see
    # installer/disko-config.nix: `mainLuksName`). The rollback hook must
    # mount the right device, otherwise initrd fails on every boot and the
    # @ → root-blank snapshot is never restored.
    mainLuksName = lib.mkOption {
      type = lib.types.str;
      default = "crypted";
      description = ''
        Name of the /dev/mapper entry holding the BTRFS root. Set to
        "crypted_main" on multi-disk installs to match the disko layout.
      '';
    };

    user = lib.mkOption {
      type = lib.types.str;
      default = "nomarchy";
      description = ''
        Primary user whose home subset (.ssh, .gnupg, keyrings, common
        directories) survives the rootfs wipe. Must match the user
        created via `users.users.<name>` — otherwise the persistence
        block is silently inert and the user's home directory is wiped
        on every boot. The installer writes this for you.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    # 1. The Rollback Service: wipes the @ root subvolume back to a blank
    #    snapshot before the real root is mounted. Plymouth enables systemd
    #    stage-1 initrd distro-wide (themes/engine/plymouth.nix), and systemd
    #    stage 1 rejects boot.initrd.postDeviceCommands — so this runs as a
    #    systemd initrd unit ordered after the LUKS mapping opens and before
    #    sysroot is mounted. initrdBin pulls in the binaries the script calls
    #    (the systemd initrd doesn't ship coreutils/findutils/btrfs by default).
    boot.initrd.systemd.initrdBin = [
      pkgs.btrfs-progs
      pkgs.coreutils
      pkgs.util-linux
      pkgs.findutils
    ];

    boot.initrd.systemd.services.nomarchy-rollback = {
      description = "Erase Your Darlings: roll the BTRFS root subvolume back to a blank snapshot";
      wantedBy = [ "initrd.target" ];
      after = [ "systemd-cryptsetup@${cfg.mainLuksName}.service" ];
      before = [ "sysroot.mount" ];
      unitConfig.DefaultDependencies = "no";
      serviceConfig.Type = "oneshot";
      script = ''
        mkdir -p /btrfs_tmp
        mount -o subvol=/ /dev/mapper/${cfg.mainLuksName} /btrfs_tmp

        if [[ -e /btrfs_tmp/@ ]]; then
            mkdir -p /btrfs_tmp/old_roots
            timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/@)" "+%Y-%m-%-d_%H:%M:%S")
            mv /btrfs_tmp/@ "/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 snapshot /btrfs_tmp/root-blank /btrfs_tmp/@
        umount /btrfs_tmp
      '';
    };

    # The impermanence module asserts that every filesystem it touches is
    # available in early boot: the persistent-storage volume (/persist) and
    # any volume it bind-mounts *into* — the user-persistence dirs land under
    # /home, so the @home subvolume counts too. disko and
    # nixos-generate-config leave neededForBoot at its default (false) on
    # these subvolumes, which trips the assertion ("Please fix the following
    # filesystems: /persist /home"). Declare it here, where the requirement
    # originates.
    fileSystems."/persist".neededForBoot = true;
    fileSystems."/home".neededForBoot = true;

    # 2. Persistence Configuration: What survives the wipe
    environment.persistence."/persist" = {
      hideMounts = true;
      directories = [
        "/var/log"
        "/var/lib/nixos"
        "/var/lib/systemd/coredump"
        "/var/lib/NetworkManager"
        "/etc/NetworkManager/system-connections"
        "/var/lib/bluetooth"
        "/var/lib/fprint"
        "/etc/nixos"
        "/etc/ssh"
      ];
      files = [
        "/etc/machine-id"
        "/etc/supergfxd.conf"
      ];
      users.${cfg.user} = {
        directories = [
          ".ssh"
          ".gnupg"
          ".local/share/keyrings"
          "Documents"
          "Downloads"
          "Pictures"
          "Videos"
          "Projects"
        ];
      };
    };
  };
}