{ diskoLib, config, options, lib, parent, device, ... }:
{
  options = {
    type = lib.mkOption {
      type = lib.types.enum [ "swap" ];
      internal = true;
      description = "Type";
    };
    device = lib.mkOption {
      type = lib.types.str;
      default = device;
      description = "Device";
    };
    discardPolicy = lib.mkOption {
      default = null;
      example = "once";
      type = lib.types.nullOr (lib.types.enum [ "once" "pages" "both" ]);
      description = lib.mdDoc ''
        Specify the discard policy for the swap device. If "once", then the
        whole swap space is discarded at swapon invocation. If "pages",
        asynchronous discard on freed pages is performed, before returning to
        the available pages pool. With "both", both policies are activated.
        See swapon(8) for more information.
      '';
    };
    extraArgs = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [ ];
      description = "Extra arguments";
    };
    priority = lib.mkOption {
      type = lib.types.nullOr lib.types.int;
      default = null;
      description = lib.mdDoc ''
        Specify the priority of the swap device. Priority is a value between 0 and 32767.
        Higher numbers indicate higher priority.
        null lets the kernel choose a priority, which will show up as a negative value.
      '';
    };
    randomEncryption = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = "Whether to randomly encrypt the swap";
    };
    resumeDevice = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = "Whether to use this as a boot.resumeDevice";
    };
    _parent = lib.mkOption {
      internal = true;
      default = parent;
    };
    _meta = lib.mkOption {
      internal = true;
      readOnly = true;
      type = lib.types.functionTo diskoLib.jsonType;
      default = _dev: { };
      description = "Metadata";
    };
    _create = diskoLib.mkCreateOption {
      inherit config options;
      default = ''
        if ! blkid "${config.device}" -o export | grep -q '^TYPE='; then
          mkswap \
            ${toString config.extraArgs} \
            ${config.device}
        fi
      '';
    };
    _mount = diskoLib.mkMountOption {
      inherit config options;
      # TODO: we don't support encrypted swap yet
      default = lib.optionalAttrs (!config.randomEncryption) {
        fs.${config.device} = ''
          if ! swapon --show | grep -q "^$(readlink -f ${config.device}) "; then
            swapon ${
              lib.optionalString (config.discardPolicy != null)
                "--discard${lib.optionalString (config.discardPolicy != "both")
                "=${config.discardPolicy}"
              }"} ${
              lib.optionalString (config.priority != null)
                "--priority=${toString config.priority}"
              } ${config.device}
          fi
        '';
      };
    };
    _config = lib.mkOption {
      internal = true;
      readOnly = true;
      default = [{
        swapDevices = [{
          device = config.device;
          inherit (config) discardPolicy priority;
          randomEncryption = {
            enable = config.randomEncryption;
            # forward discard/TRIM attempts through dm-crypt
            allowDiscards = config.discardPolicy != null;
          };
        }];
        boot.resumeDevice = lib.mkIf config.resumeDevice config.device;
      }];
      description = "NixOS configuration";
    };
    _pkgs = lib.mkOption {
      internal = true;
      readOnly = true;
      type = lib.types.functionTo (lib.types.listOf lib.types.package);
      default = pkgs: [ pkgs.gnugrep pkgs.util-linux ];
      description = "Packages";
    };
  };
}