{
  config,
  lib,
  pkgs,
  ...
}:
with lib; let
  cfg = config.local.btrfs;
in {
  options.local.btrfs = {
    snapper = mkOption {
      type = with lib.types; attrsOf str;
      default = {};
    };
  };

  config = mkIf (cfg.snapper != {}) {
    environment.systemPackages = [pkgs.local.btclone];

    services.snapper.configs = let
      snapperConfig = _: subvolume: {
        SUBVOLUME = subvolume;

        # btrfs qgroup for space aware cleanup algorithms
        QGROUP = "";

        # fraction of the filesystems space the snapshots may use
        SPACE_LIMIT = "0.5";

        # fraction of the filesystems space that should be free
        FREE_LIMIT = "0.2";

        # users and groups allowed to work with config
        ALLOW_USERS = [];
        ALLOW_GROUPS = [];

        # sync users and groups from ALLOW_USERS and ALLOW_GROUPS to .snapshots
        # directory
        SYNC_ACL = "no";

        # start comparing pre- and post-snapshot in background after creating
        # post-snapshot
        BACKGROUND_COMPARISON = "yes";

        # run daily number cleanup
        NUMBER_CLEANUP = "yes";

        # limit for number cleanup
        NUMBER_MIN_AGE = "1800";
        NUMBER_LIMIT = "100";
        NUMBER_LIMIT_IMPORTANT = "10";

        # create hourly snapshots
        TIMELINE_CREATE = true;

        # cleanup hourly snapshots after some time
        TIMELINE_CLEANUP = true;

        # limits for timeline cleanup
        TIMELINE_MIN_AGE = "1800";
        TIMELINE_LIMIT_HOURLY = "24";
        TIMELINE_LIMIT_DAILY = "7";
        TIMELINE_LIMIT_WEEKLY = "4";
        TIMELINE_LIMIT_MONTHLY = "12";
        TIMELINE_LIMIT_YEARLY = "10";

        # cleanup empty pre-post-pairs
        EMPTY_PRE_POST_CLEANUP = "yes";

        # limits for empty pre-post-pair cleanup
        EMPTY_PRE_POST_MIN_AGE = "1800";
      };
    in
      mapAttrs snapperConfig cfg.snapper;
  };
}