fava-module/fava.nix

{ config, lib, pkgs, domain ? null, ... }:

with lib;

let
  cfg = config.services.fava;

in {
  options.services.fava = {
    enable = mkEnableOption "Fava web interface for Beancount";

    ledgerFile = mkOption {
      type = types.path;
      default = "/var/lib/fava/ledger.beancount";
      description = "Path to the beancount ledger file";
    };

    host = mkOption {
      type = types.str;
      default = "127.0.0.1";
      description = "Host address to bind to";
    };

    port = mkOption {
      type = types.port;
      default = 5000;
      description = "Port to run Fava on";
    };

    user = mkOption {
      type = types.str;
      default = "fava";
      description = "User account under which Fava runs";
    };

    group = mkOption {
      type = types.str;
      default = "fava";
      description = "Group under which Fava runs";
    };

    dataDir = mkOption {
      type = types.path;
      default = "/var/lib/fava";
      description = "Directory for Fava data and ledger files";
    };

    openFirewall = mkOption {
      type = types.bool;
      default = false;
      description = "Open the firewall port for Fava";
    };

    extraOptions = mkOption {
      type = types.listOf types.str;
      default = [];
      description = "Additional command-line options to pass to Fava";
      example = [ "--read-only" "--incognito" ];
    };

    nginx = {
      enable = mkOption {
        type = types.bool;
        default = false;
        description = "Enable nginx reverse proxy for Fava";
      };

      subdomain = mkOption {
        type = types.str;
        default = "fava";
        description = "Subdomain for Fava (e.g., 'fava' for fava.domain.com)";
      };
    };
  };

  config = mkIf cfg.enable {
    # Create system user and group
    users.users.${cfg.user} = {
      isSystemUser = true;
      group = cfg.group;
      home = cfg.dataDir;
      createHome = true;
      description = "Fava service user";
    };

    users.groups.${cfg.group} = {};

    # Ensure data directory and ledger file exist with correct permissions
    systemd.tmpfiles.rules = [
      "d ${cfg.dataDir} 0750 ${cfg.user} ${cfg.group} - -"
      "f ${cfg.ledgerFile} 0640 ${cfg.user} ${cfg.group} - -"
    ];

    # Fava systemd service
    systemd.services.fava = {
      description = "Fava - Web interface for Beancount";
      after = [ "network.target" ];
      wantedBy = [ "multi-user.target" ];

      serviceConfig = {
        Type = "simple";
        User = cfg.user;
        Group = cfg.group;
        WorkingDirectory = cfg.dataDir;

        ExecStart = "${pkgs.fava}/bin/fava ${cfg.ledgerFile} --host ${cfg.host} --port ${toString cfg.port} ${concatStringsSep " " cfg.extraOptions}";

        Restart = "on-failure";
        RestartSec = "5s";

        # Security hardening
        NoNewPrivileges = true;
        PrivateHome = true;
        PrivateTmp = true;
        PrivateDevices = true;
        ProtectHome = true;
        ProtectSystem = "full";
        ProtectKernelTunables = true;
        ProtectKernelModules = true;
        ProtectControlGroups = true;
        RestrictAddressFamilies = [ "AF_UNIX" "AF_INET" "AF_INET6" ];
        RestrictNamespaces = true;
        LockPersonality = true;
        MemoryDenyWriteExecute = true;
        RestrictRealtime = true;
        RestrictSUIDSGID = true;
        PrivateMounts = true;

        # Allow read/write access to data directory
        ReadWritePaths = [ cfg.dataDir ];
      };
    };

    # Nginx reverse proxy configuration (optional)
    services.nginx.virtualHosts = mkIf (cfg.nginx.enable && domain != null) {
      "${cfg.nginx.subdomain}.${domain}" = {
        forceSSL = true;
        enableACME = true;
        locations."/" = {
          proxyPass = "http://${cfg.host}:${toString cfg.port}";
          proxyWebsockets = true;
          extraConfig = ''
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_buffering off;
          '';
        };
      };
    };

    # Open firewall port if requested
    networking.firewall.allowedTCPPorts = mkIf cfg.openFirewall [ cfg.port ];
  };
}