labmcp/nix/git-explorer-module.nix

{ config, lib, pkgs, ... }:

let
  cfg = config.services.git-explorer;

  mkHttpFlags = httpCfg: lib.concatStringsSep " " ([
    "--transport http"
    "--http-address '${httpCfg.address}'"
    "--http-endpoint '${httpCfg.endpoint}'"
    "--session-ttl '${httpCfg.sessionTTL}'"
  ] ++ lib.optionals (httpCfg.allowedOrigins != []) (
    map (origin: "--allowed-origins '${origin}'") httpCfg.allowedOrigins
  ) ++ lib.optionals httpCfg.tls.enable [
    "--tls-cert '${httpCfg.tls.certFile}'"
    "--tls-key '${httpCfg.tls.keyFile}'"
  ]);
in
{
  options.services.git-explorer = {
    enable = lib.mkEnableOption "Git Explorer MCP server";

    package = lib.mkPackageOption pkgs "git-explorer" { };

    repoPath = lib.mkOption {
      type = lib.types.str;
      description = "Path to the git repository to serve.";
    };

    defaultRemote = lib.mkOption {
      type = lib.types.str;
      default = "origin";
      description = "Default remote name for ref resolution.";
    };

    http = {
      address = lib.mkOption {
        type = lib.types.str;
        default = "127.0.0.1:8085";
        description = "HTTP listen address for the MCP server.";
      };

      endpoint = lib.mkOption {
        type = lib.types.str;
        default = "/mcp";
        description = "HTTP endpoint path for MCP requests.";
      };

      allowedOrigins = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        default = [ ];
        description = "Allowed Origin headers for CORS.";
      };

      sessionTTL = lib.mkOption {
        type = lib.types.str;
        default = "30m";
        description = "Session TTL for HTTP transport.";
      };

      tls = {
        enable = lib.mkEnableOption "TLS for HTTP transport";

        certFile = lib.mkOption {
          type = lib.types.nullOr lib.types.path;
          default = null;
          description = "Path to TLS certificate file.";
        };

        keyFile = lib.mkOption {
          type = lib.types.nullOr lib.types.path;
          default = null;
          description = "Path to TLS private key file.";
        };
      };
    };

    openFirewall = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = "Whether to open the firewall for the MCP HTTP server.";
    };
  };

  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = !cfg.http.tls.enable || (cfg.http.tls.certFile != null && cfg.http.tls.keyFile != null);
        message = "services.git-explorer.http.tls: both certFile and keyFile must be set when TLS is enabled";
      }
    ];

    systemd.services.git-explorer = {
      description = "Git Explorer MCP Server";
      wantedBy = [ "multi-user.target" ];
      after = [ "network.target" ];

      environment = {
        GIT_REPO_PATH = cfg.repoPath;
        GIT_DEFAULT_REMOTE = cfg.defaultRemote;
      };

      script = let
        httpFlags = mkHttpFlags cfg.http;
      in ''
        exec ${cfg.package}/bin/git-explorer serve ${httpFlags}
      '';

      serviceConfig = {
        Type = "simple";
        DynamicUser = true;
        Restart = "on-failure";
        RestartSec = "5s";

        # Hardening
        NoNewPrivileges = true;
        ProtectSystem = "strict";
        ProtectHome = "read-only";
        PrivateTmp = true;
        PrivateDevices = true;
        ProtectKernelTunables = true;
        ProtectKernelModules = true;
        ProtectControlGroups = true;
        RestrictNamespaces = true;
        RestrictRealtime = true;
        RestrictSUIDSGID = true;
        MemoryDenyWriteExecute = true;
        LockPersonality = true;

        # Read-only access to repo path
        ReadOnlyPaths = [ cfg.repoPath ];
      };
    };

    networking.firewall = lib.mkIf cfg.openFirewall (let
      addressParts = lib.splitString ":" cfg.http.address;
      port = lib.toInt (lib.last addressParts);
    in {
      allowedTCPPorts = [ port ];
    });
  };
}