{ lib
, pkgs
, ...
}:
{
  options = {
    environment.etc = lib.mkOption {
      default = { };
      example = lib.literalExpression ''
        { example-configuration-file =
            { source = "/nix/store/.../etc/dir/file.conf.example";
              mode = "0440";
            };
          "default/useradd".text = "GROUP=100 ...";
        }
      '';
      description = lib.mdDoc ''
        Set of files that have to be linked in {file}`/etc`.
      '';

      type = lib.types.attrsOf (lib.types.submodule (
        { name, config, options, ... }:
        {
          options = {

            enable = lib.mkOption {
              type = lib.types.bool;
              default = true;
              description = lib.mdDoc ''
                Whether this /etc file should be generated.  This
                option allows specific /etc files to be disabled.
              '';
            };

            target = lib.mkOption {
              type = lib.types.str;
              description = lib.mdDoc ''
                Name of symlink (relative to
                {file}`/etc`).  Defaults to the attribute
                name.
              '';
            };

            text = lib.mkOption {
              default = null;
              type = lib.types.nullOr lib.types.lines;
              description = lib.mdDoc "Text of the file.";
            };

            source = lib.mkOption {
              type = lib.types.path;
              description = lib.mdDoc "Path of the source file.";
            };

            mode = lib.mkOption {
              type = lib.types.str;
              default = "symlink";
              example = "0600";
              description = lib.mdDoc ''
                If set to something else than `symlink`,
                the file is copied instead of symlinked, with the given
                file mode.
              '';
            };

            uid = lib.mkOption {
              default = 0;
              type = lib.types.int;
              description = lib.mdDoc ''
                UID of created file. Only takes effect when the file is
                copied (that is, the mode is not 'symlink').
              '';
            };

            gid = lib.mkOption {
              default = 0;
              type = lib.types.int;
              description = lib.mdDoc ''
                GID of created file. Only takes effect when the file is
                copied (that is, the mode is not 'symlink').
              '';
            };

            user = lib.mkOption {
              default = "+${toString config.uid}";
              type = lib.types.str;
              description = lib.mdDoc ''
                User name of created file.
                Only takes effect when the file is copied (that is, the mode is not 'symlink').
                Changing this option takes precedence over `uid`.
              '';
            };

            group = lib.mkOption {
              default = "+${toString config.gid}";
              type = lib.types.str;
              description = lib.mdDoc ''
                Group name of created file.
                Only takes effect when the file is copied (that is, the mode is not 'symlink').
                Changing this option takes precedence over `gid`.
              '';
            };
          };

          config = {
            target = lib.mkDefault name;
            source = lib.mkIf (config.text != null) (
              let name' = "etc-" + baseNameOf name;
              in lib.mkDerivedConfig options.text (pkgs.writeText name')
            );
          };
        }
      ));
    };
  };
}