config/modules/services/deployerbot/default.nix

{
  config,
  lib,
  pkgs,
  ...
}: {
  options.mj.services.deployerbot.main = with lib.types; {
    enable = lib.mkEnableOption "Enable system updater orchestrator";
    deployDerivations = lib.mkOption {type = listOf str;};
    uidgid = lib.mkOption {type = int;};
    repo = lib.mkOption {type = str;};
  };

  options.mj.services.deployerbot.follower = with lib.types; {
    enable = lib.mkEnableOption "Allow system to be deployed with deployerbot";
    publicKey = lib.mkOption {type = str;};
    uidgid = lib.mkOption {type = int;};
  };

  config = lib.mkMerge [
    (with config.mj.services.deployerbot.main;
      lib.mkIf enable {
        # TODO: git config --global user.email bot@jakstys.lt
        users.users.deployerbot-main = {
          description = "Deployerbot Main";
          home = "/var/lib/deployerbot-main";
          useDefaultShell = true;
          group = "deployerbot-main";
          isSystemUser = true;
          createHome = true;
          uid = uidgid;
        };
        users.groups.deployerbot-main.gid = uidgid;

        systemd.services.deployerbot = {
          description = "Update all known systems";
          serviceConfig = {
            Type = "oneshot";
            User = "deployerbot-main";
            WorkingDirectory = config.users.users.deployerbot-main.home;
            LoadCredential = ["ssh-key:/etc/ssh/ssh_host_ed25519_key"];
          };
          script = let
            deployDerivationsStr = builtins.concatStringsSep " " deployDerivations;
          in ''
            set -x
            export GIT_SSH_COMMAND="${pkgs.openssh}/bin/ssh -i ''${CREDENTIALS_DIRECTORY}/ssh-key"
            if [[ ! -d config ]]; then
              ${pkgs.git}/bin/git clone ${repo} config
              cd config
            else
              cd config
              ${pkgs.git}/bin/git fetch origin
              ${pkgs.git}/bin/git reset --hard origin/main
            fi

            OLD_PATH=$PATH
            export PATH=$PATH:${pkgs.git}/bin
            ${pkgs.nix}/bin/nix flake update --accept-flake-config --commit-lock-file
            ${pkgs.git}/bin/git push origin main
            export PATH=$OLD_PATH

            export PATH=$PATH:${pkgs.git}/bin:${pkgs.openssh}/bin:${pkgs.nix}/bin
            exec ${pkgs.nix}/bin/nix run .#deploy-rs -- \
              --ssh-opts="-i ''${CREDENTIALS_DIRECTORY}/ssh-key" \
              --ssh-user=deployerbot-follower \
              ${deployDerivationsStr}
          '';
        };

        systemd.timers.deployerbot = {
          description = "deployerbot-main timer";
          wantedBy = ["timers.target"];
          # such nixpkgs commits:
          #
          #     Merge release-23.05 into staging-next-23.05
          #
          # happen at around 00:15 UTC. This is *probably* what
          # we want to follow.
          timerConfig.OnCalendar = "*-*-* 00:30:00 UTC";
        };

        mj.base.unitstatus.units = ["deployerbot"];

        nix.settings.trusted-users = ["deployerbot-main"];
      })
    (with config.mj.services.deployerbot.follower;
      lib.mkIf enable {
        users.users = {
          deployerbot-follower = {
            description = "Deployerbot Follower";
            home = "/var/lib/deployerbot-follower";
            useDefaultShell = true;
            group = "deployerbot-follower";
            extraGroups = ["wheel"];
            isSystemUser = true;
            createHome = true;
            uid = uidgid;
            openssh.authorizedKeys.keys = [publicKey];
          };
        };
        users.groups.deployerbot-follower.gid = uidgid;
      })
  ];
}