nh: add module

Add nh to news

modules/misc/news.nix

@@ -1703,6 +1703,14 @@ in {
           one place. See https://github.com/glanceapp/glance for more.
         '';
       }
+
+      {
+        time = "2024-04-23T18:50:00+00:00";
+        condition = hostPlatform.isLinux;
+        message = ''
+          A new module is available: 'programs.nh'.
+        '';
+      }
     ];
   };
 }

modules/modules.nix

@@ -169,6 +169,7 @@ let
     ./programs/neomutt.nix
     ./programs/neovim.nix
     ./programs/newsboat.nix
+    ./programs/nh.nix
     ./programs/nheko.nix
     ./programs/nix-index.nix
     ./programs/nnn.nix

modules/programs/nh.nix

@@ -0,0 +1,84 @@
+{ config, osConfig, lib, pkgs, ... }:
+
+let cfg = config.programs.nh;
+in {
+  meta.maintainers = with lib.maintainers; [ johnrtitor ];
+
+  options.programs.nh = {
+    enable = lib.mkEnableOption "nh, yet another Nix CLI helper";
+
+    package = lib.mkPackageOption pkgs "nh" { };
+
+    flake = lib.mkOption {
+      type = lib.types.nullOr lib.types.path;
+      default = null;
+      description = ''
+        The path that will be used for the `FLAKE` environment variable.
+
+        `FLAKE` is used by nh as the default flake for performing actions, like `nh os switch`.
+      '';
+    };
+
+    clean = {
+      enable = lib.mkEnableOption
+        "periodic garbage collection for user profile and nix store with nh clean user";
+
+      dates = lib.mkOption {
+        type = lib.types.singleLineStr;
+        default = "weekly";
+        description = ''
+          How often cleanup is performed. Passed to systemd.time
+
+          The format is described in
+          {manpage}`systemd.time(7)`.
+        '';
+      };
+
+      extraArgs = lib.mkOption {
+        type = lib.types.singleLineStr;
+        default = "";
+        example = "--keep 5 --keep-since 3d";
+        description = ''
+          Options given to nh clean when the service is run automatically.
+
+          See `nh clean all --help` for more information.
+        '';
+      };
+    };
+  };
+
+  config = {
+    warnings = lib.optionals (!(cfg.clean.enable -> !osConfig.nix.gc.automatic))
+      [
+        "programs.nh.clean.enable and nix.gc.automatic (system-wide in configuration.nix) are both enabled. Please use one or the other to avoid conflict."
+      ];
+
+    assertions = [{
+      assertion = (cfg.flake != null) -> !(lib.hasSuffix ".nix" cfg.flake);
+      message = "nh.flake must be a directory, not a nix file";
+    }];
+
+    home = lib.mkIf cfg.enable {
+      packages = [ cfg.package ];
+      sessionVariables = lib.mkIf (cfg.flake != null) { FLAKE = cfg.flake; };
+    };
+
+    systemd.user = lib.mkIf cfg.clean.enable {
+      services.nh-clean = {
+        Unit.Description = "Nh clean (user)";
+
+        Service = {
+          Type = "oneshot";
+          ExecStart = "exec ${lib.getExe cfg.package} clean user ${cfg.clean.extraArgs}";
+          Environment = "PATH=$PATH:${config.nix.package}";
+        };
+      };
+      timers.nh-clean = {
+        Timer = {
+          OnCalendar = cfg.clean.dates;
+          Persistent = true;
+        };
+      };
+    };
+  };
+}