{ lib, ... }:
{
  den.schema = {
    user =
      { config, ... }:
      let
        primaryEmailCount = builtins.length (lib.filter (email: email.primary) (builtins.attrValues config.emails));
      in
      {
      options = {
        realName = lib.mkOption {
          type = lib.types.str;
        };
        authorizedSshKeys = lib.mkOption {
          type = lib.types.listOf lib.types.str;
          default = [ ];
        };
        emails = lib.mkOption {
          type = lib.types.attrsOf (
            lib.types.submodule (
              { ... }:
              {
                options = {
                  address = lib.mkOption {
                    type = lib.types.str;
                  };
                  primary = lib.mkOption {
                    type = lib.types.bool;
                    default = false;
                  };
                  kind = lib.mkOption {
                    type = lib.types.enum [
                      "mxrouting"
                      "office365"
                    ];
                  };
                };
              }
            )
          );
          default = { };
        };
        syncthingId = lib.mkOption {
          type = lib.types.nullOr lib.types.str;
          default = null;
        };
      };
      config = {
        assertions = [
          {
            assertion = primaryEmailCount == 1;
            message = "Each user must define exactly one primary email.";
          }
        ];
        classes = lib.mkDefault [ "homeManager" ];
      };
    };
    host = {
      options = {
        serviceDomain = lib.mkOption {
          type = lib.types.str;
        };
        displays = lib.mkOption {
          type = lib.types.attrsOf (
            lib.types.submodule (
              { ... }:
              {
                options = {
                  position = lib.mkOption {
                    type = lib.types.submodule {
                      options = {
                        x = lib.mkOption { type = lib.types.int; };
                        y = lib.mkOption { type = lib.types.int; };
                      };
                    };
                  };
                  scale = lib.mkOption {
                    type = lib.types.nullOr (lib.types.oneOf [
                      lib.types.int
                      lib.types.float
                    ]);
                    default = null;
                  };
                  primary = lib.mkOption {
                    type = lib.types.bool;
                    default = false;
                  };
                  mode = lib.mkOption {
                    type = lib.types.nullOr (
                      lib.types.submodule (
                        { ... }:
                        {
                          options = {
                            width = lib.mkOption { type = lib.types.int; };
                            height = lib.mkOption { type = lib.types.int; };
                            refresh = lib.mkOption {
                              type = lib.types.nullOr lib.types.float;
                              default = null;
                            };
                          };
                        }
                      )
                    );
                    default = null;
                  };
                };
              }
            )
          );
          default = { };
        };
        requiresSshRecovery = lib.mkOption {
          type = lib.types.bool;
          default = false;
        };
        sshRecoveryUsers = lib.mkOption {
          type = lib.types.listOf lib.types.str;
          default = [ ];
        };
        sopsHostSshKeyPath = lib.mkOption {
          type = lib.types.nullOr lib.types.str;
          default = null;
        };
        sopsAdminKeyPath = lib.mkOption {
          type = lib.types.nullOr lib.types.str;
          default = null;
        };
        sopsAdminKeyUsers = lib.mkOption {
          type = lib.types.listOf lib.types.str;
          default = [ ];
        };
      };
    };
  };
}