{ 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;
}