Add support for NixOS (#117)

You are able to use it as standalone package, or service either.

README.md

@@ -9,6 +9,9 @@
             * [Update](#update)
          * [bpkg](#bpkg)
          * [Archlinux](#archlinux)
+         * [NixOs](#nixos)
+            * [As Module](#as-module)
+            * [As Package](#as-package)
       * [Requirements](#requirements)
          * [Notes for Mac](#notes-for-mac)
       * [What it does](#what-it-does)
@@ -84,6 +87,31 @@ the command below. You may need to invoke `bpkg` with `sudo` when using the
 There is an [AUR](https://aur.archlinux.org/packages/gitwatch-git/) package
 for Archlinux. Install it with you favorite aur helper.
 
+### NixOs
+
+#### As Module
+
+Say you add this as input `gitwatch` to your flake. Then you may want to append
+field `gitwatch.modules` to your `nixosSystem` modules. Then you are able to
+enable `services.gitwatch.*` service in per-repository mode. Like next:
+
+```nix
+services.gitwatch.my-repo = {
+    enable = true;
+    path = "/home/me/my-repo";
+    remote = "git@github.com:me/my-repo.git";
+    user = "me";
+};
+```
+
+This will make NixOS to create `systemd` service for `my-repo` repository.
+
+#### As Package
+
+You can to play around with nix package inside this repository. Call `nix run`
+in this repository to run `gitwatch` script or `nix shell` to enter shell with
+`gitwatch` command available.
+
 ## Requirements
 
 To run this script, you must have installed and globally available:

flake.nix

@@ -0,0 +1,19 @@
+{
+  description = "A bash script to watch a file or folder and commit changes to a git repo";
+  outputs = { self, nixpkgs, flake-utils }:
+    let
+      packages = flake-utils.lib.eachDefaultSystem (system:
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+          };
+        in
+        {
+          packages = rec {
+            gitwatch = pkgs.callPackage ./gitwatch.sh { };
+            default = gitwatch;
+          };
+        });
+    in
+    packages // { modules = [ ./module.nix ]; };
+}

gitwatch.nix

@@ -0,0 +1,19 @@
+{ runCommandNoCC
+, lib
+, makeWrapper
+
+, git
+, openssh
+, inotify-tools
+}: runCommandNoCC "gitwatch" {
+  nativeBuildInputs = [ makeWrapper ];
+} ''
+  mkdir -p $out/bin
+  dest="$out/bin/gitwatch"
+  cp ${./gitwatch.sh} $dest
+  chmod +x $dest
+  patchShebangs $dest
+
+  wrapProgram $dest \
+    --prefix PATH ';' ${lib.makeBinPath [ git inotify-tools openssh ]}
+''

module.nix

@@ -0,0 +1,84 @@
+{ lib, pkgs, config, ... }:
+let
+  gitwatch = pkgs.callPackage ./gitwatch.nix { };
+  mkSystemdService = name: cfg: lib.nameValuePair
+    "gitwatch-${name}"
+    (
+      let
+        getvar = flag: var:
+          if cfg."${var}" != null
+          then "${flag} ${cfg."${var}"}"
+          else "";
+        branch = getvar "-b" "branch";
+        fetcher =
+          if cfg.remote == null
+          then "true"
+          else ''
+          '';
+      in
+      {
+        inherit (cfg) enable;
+        after = [ "network-online.target" ];
+        description = "gitwatch for ${name}";
+        path = with pkgs; [ gitwatch git openssh ];
+        script = ''
+          if [ -n "${cfg.remote}" ] && ! [ -d "${cfg.path}" ]; then
+            git clone ${branch} "${cfg.remote}" "${cfg.path}"
+          fi
+          ${fetcher}
+          gitwatch ${getvar "-r" "remote"} ${branch} ${cfg.path}
+        '';
+        serviceConfig.User = cfg.user;
+      }
+    );
+in
+{
+  options.services.gitwatch = lib.mkOption {
+    description = ''
+      A set of git repositories to watch for. See
+      [gitwatch](https://github.com/gitwatch/gitwatch) for more.
+    '';
+    default = { };
+    example = {
+      my-repo = {
+        enable = true;
+        user = "user";
+        path = "/home/user/watched-project";
+        remote = "git@github.com:me/my-project.git";
+      };
+      disabled-repo = {
+        enable = false;
+        user = "user";
+        path = "/home/user/disabled-project";
+        remote = "git@github.com:me/my-old-project.git";
+        branch = "autobranch";
+      };
+    };
+    type = with lib.types; attrsOf (submodule {
+      options = {
+        enable = lib.mkEnableOption "watching for repo";
+        path = lib.mkOption {
+          description = "The path to repo in local machine";
+          type = str;
+        };
+        user = lib.mkOption {
+          description = "The name of services's user";
+          type = str;
+          default = "root";
+        };
+        remote = lib.mkOption {
+          description = "Optional url of remote repository";
+          type = nullOr str;
+          default = null;
+        };
+        branch = lib.mkOption {
+          description = "Optional branch in remote repository";
+          type = nullOr str;
+          default = null;
+        };
+      };
+    });
+  };
+  config.systemd.services =
+    lib.mapAttrs' mkSystemdService config.services.gitwatch;
+}