nixos/modules/services/snapper.nix

inputs:
{
  options.nixos.services.snapper = let inherit (inputs.lib) mkOption types; in
  {
    enable = mkOption { type = types.bool; default = false; };
    configs = mkOption { type = types.attrsOf types.nonEmptyStr; default = {}; };
  };
  config =
    let
      inherit (inputs.lib) mkMerge mkIf;
      inherit (inputs.localLib) stripeTabs attrsToList;
      inherit (inputs.config.nixos) services;
      inherit (builtins) map listToAttrs toString;
    in mkIf services.snapper.enable
    {
      services.snapper.configs =
        let
          f = (config:
          {
            inherit (config) name;
            value =
            {
              SUBVOLUME = config.value;
              TIMELINE_CREATE = true;
              TIMELINE_CLEANUP = true;
              TIMELINE_MIN_AGE = 1800;
              TIMELINE_LIMIT_HOURLY = "10";
              TIMELINE_LIMIT_DAILY = "7";
              TIMELINE_LIMIT_WEEKLY = "1";
              TIMELINE_LIMIT_MONTHLY = "0";
              TIMELINE_LIMIT_YEARLY = "0";
            };
          });
        in
          listToAttrs (map f (attrsToList services.snapper.configs));
    };
}