{ config, lib, pkgs, ... }:
let
  cfg = config.services.mullvad-vpn;
in
with lib;
{
  options.services.mullvad-vpn = {
    enable = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        This option enables Mullvad VPN daemon.
        This sets {option}`networking.firewall.checkReversePath` to "loose", which might be undesirable for security.
      '';
    };

    package = mkOption {
      type = types.package;
      default = pkgs.mullvad;
      defaultText = literalExpression "pkgs.mullvad";
      description = lib.mdDoc ''
        The Mullvad package to use. `pkgs.mullvad` only provides the CLI tool, `pkgs.mullvad-vpn` provides both the CLI and the GUI.
      '';
    };
  };

  config = mkIf cfg.enable {
    boot.kernelModules = [ "tun" ];

    # mullvad-daemon writes to /etc/iproute2/rt_tables
    networking.iproute2.enable = true;

    # See https://github.com/NixOS/nixpkgs/issues/113589
    networking.firewall.checkReversePath = "loose";

    systemd.services.mullvad-daemon = {
      description = "Mullvad VPN daemon";
      wantedBy = [ "multi-user.target" ];
      wants = [ "network.target" ];
      after = [
        "network-online.target"
        "NetworkManager.service"
        "systemd-resolved.service"
      ];
      path = [
        pkgs.iproute2
        # Needed for ping
        "/run/wrappers"
      ];
      startLimitBurst = 5;
      startLimitIntervalSec = 20;
      serviceConfig = {
        ExecStart = "${cfg.package}/bin/mullvad-daemon -v --disable-stdout-timestamps";
        Restart = "always";
        RestartSec = 1;
      };
    };
  };

  meta.maintainers = with maintainers; [ patricksjackson ymarkus ];
}