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

with pkgs;
with lib;

let
  cfg = config.networking.networkmanager;

  stateDirs = "/var/lib/NetworkManager /var/lib/dhclient";

  configFile = writeText "NetworkManager.conf" ''
    [main]
    plugins=keyfile

    [keyfile]
    ${optionalString (config.networking.hostName != "") ''
      hostname=${config.networking.hostName}
    ''}

    [logging]
    level=WARN
  '';

  /*
    [network-manager]
    Identity=unix-group:networkmanager
    Action=org.freedesktop.NetworkManager.*
    ResultAny=yes
    ResultInactive=no
    ResultActive=yes

    [modem-manager]
    Identity=unix-group:networkmanager
    Action=org.freedesktop.ModemManager*
    ResultAny=yes
    ResultInactive=no
    ResultActive=yes
  */
  polkitConf = ''
    polkit.addRule(function(action, subject) {
      if (
        subject.isInGroup("networkmanager")
        && subject.active
        && (action.id.indexOf("org.freedesktop.NetworkManager.") == 0
            || action.id.indexOf("org.freedesktop.ModemManager")  == 0
        ))
          { return polkit.Result.YES; }
    });
  '';

  ipUpScript = writeScript "01nixos-ip-up" ''
    #!/bin/sh
    if test "$2" = "up"; then
      ${config.systemd.package}/bin/systemctl start ip-up.target
    fi
  '';

  ns = xs: writeText "nameservers" (
    concatStrings (map (s: "nameserver ${s}\n") xs)
  );

  overrideNameserversScript = writeScript "02overridedns" ''
    #!/bin/sh
    tmp=`${coreutils}/bin/mktemp`
    ${gnused}/bin/sed '/nameserver /d' /etc/resolv.conf > $tmp
    ${gnugrep}/bin/grep 'nameserver ' /etc/resolv.conf | \
      ${gnugrep}/bin/grep -vf ${ns (cfg.appendNameservers ++ cfg.insertNameservers)} > $tmp.ns
    ${optionalString (cfg.appendNameservers != []) "${coreutils}/bin/cat $tmp $tmp.ns ${ns cfg.appendNameservers} > /etc/resolv.conf"}
    ${optionalString (cfg.insertNameservers != []) "${coreutils}/bin/cat $tmp ${ns cfg.insertNameservers} $tmp.ns > /etc/resolv.conf"}
    ${coreutils}/bin/rm -f $tmp $tmp.ns
  '';

in {

  ###### interface

  options = {

    networking.networkmanager = {

      enable = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Whether to use NetworkManager to obtain an IP address and other
          configuration for all network interfaces that are not manually
          configured. If enabled, a group <literal>networkmanager</literal>
          will be created. Add all users that should have permission
          to change network settings to this group.
        '';
      };

      packages = mkOption {
        type = types.listOf types.path;
        default = [ ];
        description = ''
          Extra packages that provide NetworkManager plugins.
        '';
        apply = list: [ networkmanager modemmanager wpa_supplicant ] ++ list;
      };

      appendNameservers = mkOption {
        type = types.listOf types.string;
        default = [];
        description = ''
          A list of name servers that should be appended
          to the ones configured in NetworkManager or received by DHCP.
        '';
      };

      insertNameservers = mkOption {
        type = types.listOf types.string;
        default = [];
        description = ''
          A list of name servers that should be inserted before
          the ones configured in NetworkManager or received by DHCP.
        '';
      };

    };
  };


  ###### implementation

  config = mkIf cfg.enable {

    assertions = [{
      assertion = config.networking.wireless.enable == false;
      message = "You can not use networking.networkmanager with services.networking.wireless";
    }];

    boot.kernelModules = [ "ppp_mppe" ]; # Needed for most (all?) PPTP VPN connections.

    environment.etc = [
      { source = ipUpScript;
        target = "NetworkManager/dispatcher.d/01nixos-ip-up";
      }
      { source = configFile;
        target = "NetworkManager/NetworkManager.conf";
      }
      { source = "${networkmanager_openvpn}/etc/NetworkManager/VPN/nm-openvpn-service.name";
        target = "NetworkManager/VPN/nm-openvpn-service.name";
      }
      { source = "${networkmanager_vpnc}/etc/NetworkManager/VPN/nm-vpnc-service.name";
        target = "NetworkManager/VPN/nm-vpnc-service.name";
      }
      { source = "${networkmanager_openconnect}/etc/NetworkManager/VPN/nm-openconnect-service.name";
        target = "NetworkManager/VPN/nm-openconnect-service.name";
      }
      { source = "${networkmanager_pptp}/etc/NetworkManager/VPN/nm-pptp-service.name";
        target = "NetworkManager/VPN/nm-pptp-service.name";
      }
    ] ++ optional (cfg.appendNameservers == [] || cfg.insertNameservers == [])
           { source = overrideNameserversScript;
             target = "NetworkManager/dispatcher.d/02overridedns";
           };

    environment.systemPackages = cfg.packages ++ [
        networkmanager_openvpn
        networkmanager_vpnc
        networkmanager_openconnect
        networkmanager_pptp
        modemmanager
        ];

    users.extraGroups = singleton {
      name = "networkmanager";
      gid = config.ids.gids.networkmanager;
    };

    systemd.packages = cfg.packages;

    # Create an initialisation service that both starts
    # NetworkManager when network.target is reached,
    # and sets up necessary directories for NM.
    systemd.services."networkmanager-init" = {
      description = "NetworkManager initialisation";
      wantedBy = [ "network.target" ];
      wants = [ "NetworkManager.service" ];
      before = [ "NetworkManager.service" ];
      script = ''
        mkdir -m 700 -p /etc/NetworkManager/system-connections
        mkdir -m 755 -p ${stateDirs}
      '';
      serviceConfig.Type = "oneshot";
    };

    # Turn off NixOS' network management
    networking = {
      useDHCP = false;
      wireless.enable = false;
    };

    powerManagement.resumeCommands = ''
      systemctl restart NetworkManager
    '';

    security.polkit.extraConfig = polkitConf;

    # openvpn plugin has only dbus interface
    services.dbus.packages = cfg.packages ++ [
        networkmanager_openvpn
        networkmanager_vpnc
        networkmanager_openconnect
        networkmanager_pptp
        modemmanager
        ];

    services.udev.packages = cfg.packages;
  };
}