{ config, lib, pkgs, ... }:
let
  cfg = config.services.clamsmtp;
  clamdSocket = "/run/clamav/clamd.ctl"; # See services/security/clamav.nix
in
{
  ##### interface
  options = {
    services.clamsmtp = {
      enable = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to enable clamsmtp.";
      };

      instances = lib.mkOption {
        description = "Instances of clamsmtp to run.";
        type = lib.types.listOf (lib.types.submodule { options = {
          action = lib.mkOption {
            type = lib.types.enum [ "bounce" "drop" "pass" ];
            default = "drop";
            description = ''
                Action to take when a virus is detected.

                Note that viruses often spoof sender addresses, so bouncing is
                in most cases not a good idea.
              '';
          };

          header = lib.mkOption {
            type = lib.types.str;
            default = "";
            example = "X-Virus-Scanned: ClamAV using ClamSMTP";
            description = ''
                A header to add to scanned messages. See clamsmtpd.conf(5) for
                more details. Empty means no header.
              '';
          };

          keepAlives = lib.mkOption {
            type = lib.types.int;
            default = 0;
            description = ''
                Number of seconds to wait between each NOOP sent to the sending
                server. 0 to disable.

                This is meant for slow servers where the sending MTA times out
                waiting for clamd to scan the file.
              '';
          };

          listen = lib.mkOption {
            type = lib.types.str;
            example = "127.0.0.1:10025";
            description = ''
                Address to wait for incoming SMTP connections on. See
                clamsmtpd.conf(5) for more details.
              '';
          };

          quarantine = lib.mkOption {
            type = lib.types.bool;
            default = false;
            description = ''
                Whether to quarantine files that contain viruses by leaving them
                in the temporary directory.
              '';
          };

          maxConnections = lib.mkOption {
            type = lib.types.int;
            default = 64;
            description = "Maximum number of connections to accept at once.";
          };

          outAddress = lib.mkOption {
            type = lib.types.str;
            description = ''
                Address of the SMTP server to send email to once it has been
                scanned.
              '';
          };

          tempDirectory = lib.mkOption {
            type = lib.types.str;
            default = "/tmp";
            description = ''
                Temporary directory that needs to be accessible to both clamd
                and clamsmtpd.
              '';
          };

          timeout = lib.mkOption {
            type = lib.types.int;
            default = 180;
            description = "Time-out for network connections.";
          };

          transparentProxy = lib.mkOption {
            type = lib.types.bool;
            default = false;
            description = "Enable clamsmtp's transparent proxy support.";
          };

          virusAction = lib.mkOption {
            type = with lib.types; nullOr path;
            default = null;
            description = ''
                Command to run when a virus is found. Please see VIRUS ACTION in
                clamsmtpd(8) for a discussion of this option and its safe use.
              '';
          };

          xClient = lib.mkOption {
            type = lib.types.bool;
            default = false;
            description = ''
                Send the XCLIENT command to the receiving server, for forwarding
                client addresses and connection information if the receiving
                server supports this feature.
              '';
          };
        };});
      };
    };
  };

  ##### implementation
  config = let
    configfile = conf: pkgs.writeText "clamsmtpd.conf"
      ''
        Action: ${conf.action}
        ClamAddress: ${clamdSocket}
        Header: ${conf.header}
        KeepAlives: ${toString conf.keepAlives}
        Listen: ${conf.listen}
        Quarantine: ${if conf.quarantine then "on" else "off"}
        MaxConnections: ${toString conf.maxConnections}
        OutAddress: ${conf.outAddress}
        TempDirectory: ${conf.tempDirectory}
        TimeOut: ${toString conf.timeout}
        TransparentProxy: ${if conf.transparentProxy then "on" else "off"}
        User: clamav
        ${lib.optionalString (conf.virusAction != null) "VirusAction: ${conf.virusAction}"}
        XClient: ${if conf.xClient then "on" else "off"}
      '';
  in
    lib.mkIf cfg.enable {
      assertions = [
        { assertion = config.services.clamav.daemon.enable;
          message = "clamsmtp requires clamav to be enabled";
        }
      ];

      systemd.services = lib.listToAttrs (lib.imap1 (i: conf:
        lib.nameValuePair "clamsmtp-${toString i}" {
          description = "ClamSMTP instance ${toString i}";
          wantedBy = [ "multi-user.target" ];
          script = "exec ${pkgs.clamsmtp}/bin/clamsmtpd -f ${configfile conf}";
          after = [ "clamav-daemon.service" ];
          requires = [ "clamav-daemon.service" ];
          serviceConfig.Type = "forking";
          serviceConfig.PrivateTmp = "yes";
          unitConfig.JoinsNamespaceOf = "clamav-daemon.service";
        }
      ) cfg.instances);
    };

  meta.maintainers = with lib.maintainers; [ ekleog ];
}
