# D-Bus configuration and system bus daemon.

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

with lib;

let

  cfg = config.services.dbus;

  homeDir = "/var/run/dbus";

  systemExtraxml = concatStrings (flip concatMap cfg.packages (d: [
    "<servicedir>${d}/share/dbus-1/system-services</servicedir>"
    "<includedir>${d}/etc/dbus-1/system.d</includedir>"
  ]));

  sessionExtraxml = concatStrings (flip concatMap cfg.packages (d: [
    "<servicedir>${d}/share/dbus-1/services</servicedir>"
    "<includedir>${d}/etc/dbus-1/session.d</includedir>"
  ]));

  configDir = pkgs.stdenv.mkDerivation {
    name = "dbus-conf";

    preferLocalBuild = true;
    allowSubstitutes = false;

    buildCommand = ''
      mkdir -p $out

      sed '${./dbus-system-local.conf.in}' \
        -e 's,@servicehelper@,${config.security.wrapperDir}/dbus-daemon-launch-helper,g' \
        -e 's,@extra@,${systemExtraxml},' \
        > "$out/system-local.conf"

      sed '${./dbus-session-local.conf.in}' \
        -e 's,@extra@,${sessionExtraxml},' \
        > "$out/session-local.conf"
    '';
  };

in

{

  ###### interface

  options = {

    services.dbus = {

      enable = mkOption {
        type = types.bool;
        default = false;
        internal = true;
        description = ''
          Whether to start the D-Bus message bus daemon, which is
          required by many other system services and applications.
        '';
      };

      packages = mkOption {
        type = types.listOf types.path;
        default = [ ];
        description = ''
          Packages whose D-Bus configuration files should be included in
          the configuration of the D-Bus system-wide or session-wide
          message bus.  Specifically, files in the following directories
          will be included into their respective DBus configuration paths:
          <filename><replaceable>pkg</replaceable>/etc/dbus-1/system.d</filename>
          <filename><replaceable>pkg</replaceable>/share/dbus-1/system-services</filename>
          <filename><replaceable>pkg</replaceable>/etc/dbus-1/session.d</filename>
          <filename><replaceable>pkg</replaceable>/share/dbus-1/services</filename>
        '';
      };

    };

  };


  ###### implementation

  config = mkIf cfg.enable {

    environment.systemPackages = [ pkgs.dbus.daemon pkgs.dbus_tools ];

    environment.etc = singleton
      { source = configDir;
        target = "dbus-1";
      };

    users.extraUsers.messagebus = {
      uid = config.ids.uids.messagebus;
      description = "D-Bus system message bus daemon user";
      home = homeDir;
      group = "messagebus";
    };

    users.extraGroups.messagebus.gid = config.ids.gids.messagebus;

    systemd.packages = [ pkgs.dbus.daemon ];

    security.setuidOwners = singleton
      { program = "dbus-daemon-launch-helper";
        source = "${pkgs.dbus_daemon.out}/libexec/dbus-daemon-launch-helper";
        owner = "root";
        group = "messagebus";
        setuid = true;
        setgid = false;
        permissions = "u+rx,g+rx,o-rx";
      };

    services.dbus.packages = [
      pkgs.dbus.out
      config.system.path
    ];

    # Don't restart dbus-daemon. Bad things tend to happen if we do.
    systemd.services.dbus.reloadIfChanged = true;

    systemd.services.dbus.restartTriggers = [ configDir ];

    environment.pathsToLink = [ "/etc/dbus-1" "/share/dbus-1" ];

  };

}