{ config, lib, pkgs, ... }:

with lib;

let

  cfg = config.home;

  dag = config.lib.dag;

  languageSubModule = types.submodule {
    options = {
      base = mkOption {
        default = null;
        type = types.nullOr types.str;
        description = ''
          The language to use unless overridden by a more specific option.
        '';
      };

      address = mkOption {
        default = null;
        type = types.nullOr types.str;
        description = ''
          The language to use for addresses.
        '';
      };

      monetary = mkOption {
        default = null;
        type = types.nullOr types.str;
        description = ''
          The language to use for formatting currencies and money amounts.
        '';
      };

      paper = mkOption {
        default = null;
        type = types.nullOr types.str;
        description = ''
          The language to use for paper sizes.
        '';
      };

      time = mkOption {
        default = null;
        type = types.nullOr types.str;
        description = ''
          The language to use for formatting times.
        '';
      };
    };
  };

  keyboardSubModule = types.submodule {
    options = {
      layout = mkOption {
        type = with types; nullOr str;
        default =
          if versionAtLeast config.home.stateVersion "19.09"
          then null
          else "us";
        defaultText = literalExample "null";
        description = ''
          Keyboard layout. If <literal>null</literal>, then the system
          configuration will be used.
          </para><para>
          This defaults to <literal>null</literal> for state
          version ≥ 19.09 and <literal>"us"</literal> otherwise.
        '';
      };

      model = mkOption {
        type = with types; nullOr str;
        default = null;
        example = "presario";
        description = ''
          Keyboard model.
        '';
      };

      options = mkOption {
        type = types.listOf types.str;
        default = [];
        example = ["grp:caps_toggle" "grp_led:scroll"];
        description = ''
          X keyboard options; layout switching goes here.
        '';
      };

      variant = mkOption {
        type = with types; nullOr str;
        default =
          if versionAtLeast config.home.stateVersion "19.09"
          then null
          else "";
        defaultText = literalExample "null";
        example = "colemak";
        description = ''
          X keyboard variant. If <literal>null</literal>, then the
          system configuration will be used.
          </para><para>
          This defaults to <literal>null</literal> for state
          version ≥ 19.09 and <literal>""</literal> otherwise.
        '';
      };
    };
  };

in

{
  meta.maintainers = [ maintainers.rycee ];

  imports = [
    (mkRemovedOptionModule [ "home" "sessionVariableSetter" ] ''
      Session variables are now always set through the shell. This is
      done automatically if the shell configuration is managed by Home
      Manager. If not, then you must source the

        ~/.nix-profile/etc/profile.d/hm-session-vars.sh

      file yourself.
    '')
  ];

  options = {
    home.username = mkOption {
      type = types.str;
      defaultText = "$USER";
      description = "The user's username.";
    };

    home.homeDirectory = mkOption {
      type = types.path;
      defaultText = "$HOME";
      description = "The user's home directory.";
    };

    home.profileDirectory = mkOption {
      type = types.path;
      defaultText = "~/.nix-profile";
      internal = true;
      readOnly = true;
      description = ''
        The profile directory where Home Manager generations are
        installed.
      '';
    };

    home.language = mkOption {
      type = languageSubModule;
      default = {};
      description = "Language configuration.";
    };

    home.keyboard = mkOption {
      type = types.nullOr keyboardSubModule;
      default = {};
      description = ''
        Keyboard configuration. Set to <literal>null</literal> to
        disable Home Manager keyboard management.
      '';
    };

    home.sessionVariables = mkOption {
      default = {};
      type = types.attrs;
      example = { EDITOR = "emacs"; GS_OPTIONS = "-sPAPERSIZE=a4"; };
      description = ''
        Environment variables to always set at login.
        </para><para>
        The values may refer to other environment variables using
        POSIX.2 style variable references. For example, a variable
        <varname>parameter</varname> may be referenced as
        <code>$parameter</code> or <code>''${parameter}</code>. A
        default value <literal>foo</literal> may be given as per
        <code>''${parameter:-foo}</code> and, similarly, an alternate
        value <literal>bar</literal> can be given as per
        <code>''${parameter:+bar}</code>.
        </para><para>
        Note, these variables may be set in any order so no session
        variable may have a runtime dependency on another session
        variable. In particular code like
        <programlisting language="nix">
        home.sessionVariables = {
          FOO = "Hello";
          BAR = "$FOO World!";
        };
        </programlisting>
        may not work as expected. If you need to reference another
        session variable, then do so inside Nix instead. The above
        example then becomes
        <programlisting language="nix">
        home.sessionVariables = {
          FOO = "Hello";
          BAR = "''${config.home.sessionVariables.FOO} World!";
        };
        </programlisting>
      '';
    };

    home.packages = mkOption {
      type = types.listOf types.package;
      default = [];
      description = "The set of packages to appear in the user environment.";
    };

    home.extraOutputsToInstall = mkOption {
      type = types.listOf types.str;
      default = [];
      example = [ "doc" "info" "devdoc" ];
      description = ''
        List of additional package outputs of the packages
        <varname>home.packages</varname> that should be installed into
        the user environment.
      '';
    };

    home.path = mkOption {
      internal = true;
      description = "The derivation installing the user packages.";
    };

    home.emptyActivationPath = mkOption {
      internal = true;
      default = false;
      type = types.bool;
      description = ''
        Whether the activation script should start with an empty
        <envvar>PATH</envvar> variable. When <literal>false</literal>
        then the user's <envvar>PATH</envvar> will be used.
      '';
    };

    home.activation = mkOption {
      internal = true;
      default = {};
      type = types.attrs;
      description = ''
        Activation scripts for the home environment.
        </para><para>
        Any script should respect the <varname>DRY_RUN</varname>
        variable, if it is set then no actual action should be taken.
        The variable <varname>DRY_RUN_CMD</varname> is set to
        <code>echo</code> if dry run is enabled. Thus, many cases you
        can use the idiom <code>$DRY_RUN_CMD rm -rf /</code>.
      '';
    };

    home.activationPackage = mkOption {
      internal = true;
      type = types.package;
      description = "The package containing the complete activation script.";
    };

    home.extraBuilderCommands = mkOption {
      type = types.lines;
      default = "";
      internal = true;
      description = ''
        Extra commands to run in the Home Manager generation builder.
      '';
    };

    home.extraProfileCommands = mkOption {
      type = types.lines;
      default = "";
      internal = true;
      description = ''
        Extra commands to run in the Home Manager profile builder.
      '';
    };
  };

  config = {
    assertions = [
      {
        assertion = config.home.username != "";
        message = "Username could not be determined";
      }
      {
        assertion = config.home.homeDirectory != "";
        message = "Home directory could not be determined";
      }
    ];

    home.username = mkDefault (builtins.getEnv "USER");
    home.homeDirectory = mkDefault (builtins.getEnv "HOME");

    home.profileDirectory =
      if config.submoduleSupport.enable
        && config.submoduleSupport.externalPackageInstall
      then config.home.path
      else cfg.homeDirectory + "/.nix-profile";

    home.sessionVariables =
      let
        maybeSet = n: v: optionalAttrs (v != null) { ${n} = v; };
      in
        (maybeSet "LANG" cfg.language.base)
        //
        (maybeSet "LC_ADDRESS" cfg.language.address)
        //
        (maybeSet "LC_MONETARY" cfg.language.monetary)
        //
        (maybeSet "LC_PAPER" cfg.language.paper)
        //
        (maybeSet "LC_TIME" cfg.language.time);

    home.packages = [
      # Provide a file holding all session variables.
      (
        pkgs.writeTextFile {
          name = "hm-session-vars.sh";
          destination = "/etc/profile.d/hm-session-vars.sh";
          text = ''
            # Only source this once.
            if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
            export __HM_SESS_VARS_SOURCED=1

            ${config.lib.shell.exportAll cfg.sessionVariables}
          '';
        }
      )
    ];

    # A dummy entry acting as a boundary between the activation
    # script's "check" and the "write" phases.
    home.activation.writeBoundary = dag.entryAnywhere "";

    # Install packages to the user environment.
    #
    # Note, sometimes our target may not allow modification of the Nix
    # store and then we cannot rely on `nix-env -i`. This is the case,
    # for example, if we are running as a NixOS module and building a
    # virtual machine. Then we must instead rely on an external
    # mechanism for installing packages, which in NixOS is provided by
    # the `users.users.<name?>.packages` option. The activation
    # command is still needed since some modules need to run their
    # activation commands after the packages are guaranteed to be
    # installed.
    #
    # In case the user has moved from a user-install of Home Manager
    # to a submodule managed one we attempt to uninstall the
    # `home-manager-path` package if it is installed.
    home.activation.installPackages = dag.entryAfter ["writeBoundary"] (
      if config.submoduleSupport.externalPackageInstall
      then
        ''
          if nix-env -q | grep '^home-manager-path$'; then
            $DRY_RUN_CMD nix-env -e home-manager-path
          fi
        ''
      else
        ''
          $DRY_RUN_CMD nix-env -i ${cfg.path}
        ''
    );

    home.activationPackage =
      let
        mkCmd = res: ''
            noteEcho Activating ${res.name}
            ${res.data}
          '';
        sortedCommands = dag.topoSort cfg.activation;
        activationCmds =
          if sortedCommands ? result then
            concatStringsSep "\n" (map mkCmd sortedCommands.result)
          else
            abort ("Dependency cycle in activation script: "
              + builtins.toJSON sortedCommands);

        # Programs that always should be available on the activation
        # script's PATH.
        activationBinPaths = lib.makeBinPath [
          pkgs.bash
          pkgs.coreutils
          pkgs.diffutils        # For `cmp` and `diff`.
          pkgs.findutils
          pkgs.gnugrep
          pkgs.gnused
          pkgs.ncurses          # For `tput`.
        ]
        + optionalString (!cfg.emptyActivationPath) "\${PATH:+:}$PATH";

        activationScript = pkgs.writeScript "activation-script" ''
          #!${pkgs.runtimeShell}

          set -eu
          set -o pipefail

          cd $HOME

          export PATH="${activationBinPaths}"

          . ${./lib-bash/color-echo.sh}

          ${builtins.readFile ./lib-bash/activation-init.sh}

          ${activationCmds}
        '';
      in
        pkgs.runCommand
          "home-manager-generation"
          {
            preferLocalBuild = true;
            allowSubstitutes = false;
          }
          ''
            mkdir -p $out

            cp ${activationScript} $out/activate

            substituteInPlace $out/activate \
              --subst-var-by GENERATION_DIR $out

            ln -s ${config.home-files} $out/home-files
            ln -s ${cfg.path} $out/home-path

            ${cfg.extraBuilderCommands}
          '';

    home.path = pkgs.buildEnv {
      name = "home-manager-path";

      paths = cfg.packages;
      inherit (cfg) extraOutputsToInstall;

      postBuild = cfg.extraProfileCommands;

      meta = {
        description = "Environment of packages installed through home-manager";
      };
    };
  };
}