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

let
  cfg = config.services.kotsukotsu;
  launcher = pkgs.writeShellScript "kotsukotsu-launch" ''
    exec ${cfg.currentPath}/bin/kotsukotsu
  '';
  ensureCurrent = pkgs.writeShellScript "kotsukotsu-ensure-current" ''
    if [ ! -e ${cfg.currentPath} ]; then
      ln -sfn ${cfg.package} ${cfg.currentPath}
    fi
  '';
in
{
  options.services.kotsukotsu = {
    enable = lib.mkEnableOption "kotsukotsu typing app";

    package = lib.mkOption {
      type = lib.types.nullOr lib.types.package;
      default = null;
      description = "The kotsukotsu package to run, typically inputs.kotsukotsu.packages.${pkgs.system}.default.";
    };

    host = lib.mkOption {
      type = lib.types.str;
      default = "127.0.0.1";
      description = "Listen address for the Bun server.";
    };

    port = lib.mkOption {
      type = lib.types.port;
      default = 5174;
      description = "Listen port for the Bun server.";
    };

    domain = lib.mkOption {
      type = lib.types.nullOr lib.types.str;
      default = null;
      example = "typing.example.com";
      description = "Public domain used for WebAuthn RP ID and cookie origin.";
    };

    dataDir = lib.mkOption {
      type = lib.types.str;
      default = "/var/lib/kotsukotsu";
      description = "Directory for the persistent SQLite database.";
    };

    currentPath = lib.mkOption {
      type = lib.types.str;
      default = "/var/lib/kotsukotsu/current";
      description = "Stable symlink path that points at the active app package.";
    };

    user = lib.mkOption {
      type = lib.types.str;
      default = "kotsukotsu";
      description = "User account for the service.";
    };

    group = lib.mkOption {
      type = lib.types.str;
      default = "kotsukotsu";
      description = "Group for the service.";
    };

    secureCookies = lib.mkOption {
      type = lib.types.bool;
      default = true;
      description = "Whether to mark auth cookies as Secure.";
    };
  };

  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = cfg.package != null;
        message = "services.kotsukotsu.package must be set, usually from this flake input.";
      }
      {
        assertion = cfg.domain != null && cfg.domain != "";
        message = "services.kotsukotsu.domain must be set.";
      }
      {
        assertion = lib.hasPrefix "/" cfg.dataDir;
        message = "services.kotsukotsu.dataDir must be an absolute path.";
      }
      {
        assertion = lib.hasPrefix "/" cfg.currentPath;
        message = "services.kotsukotsu.currentPath must be an absolute path.";
      }
    ];

    users.groups = lib.mkIf (cfg.group == "kotsukotsu") {
      kotsukotsu = { };
    };

    users.users = lib.mkIf (cfg.user == "kotsukotsu") {
      kotsukotsu = {
        isSystemUser = true;
        group = cfg.group;
        home = toString cfg.dataDir;
        createHome = false;
      };
    };

    systemd.tmpfiles.rules = [
      "d ${toString cfg.dataDir} 0750 ${cfg.user} ${cfg.group} -"
    ];

    systemd.services.kotsukotsu = {
      description = "kotsukotsu typing app";
      after = [ "network.target" ];
      wantedBy = [ "multi-user.target" ];

      environment = {
        APP_ORIGIN = "https://${cfg.domain}";
        HOST = cfg.host;
        PORT = builtins.toString cfg.port;
        SESSION_COOKIE_SECURE = lib.boolToString cfg.secureCookies;
        SQLITE_PATH = "${cfg.dataDir}/leo-typing.db";
      };

      serviceConfig = {
        ExecStart = launcher;
        ExecStartPre = ensureCurrent;
        Group = cfg.group;
        Restart = "on-failure";
        User = cfg.user;
        WorkingDirectory = cfg.dataDir;
      };
    };
  };
}