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

with lib;

let cfg = config.documentation; in

{

  options = {

    documentation = {

      enable = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Whether to install documentation of packages from
          <option>environment.systemPackages</option> into the generated system path.

          See "Multiple-output packages" chapter in the nixpkgs manual for more info.
        '';
        # which is at ../../../doc/multiple-output.xml
      };

      man.enable = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Whether to install manual pages and the <command>man</command> command.
          This also includes "man" outputs.
        '';
      };

      info.enable = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Whether to install info pages and the <command>info</command> command.
          This also includes "info" outputs.
        '';
      };

      doc.enable = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Whether to install documentation distributed in packages' <literal>/share/doc</literal>.
          Usually plain text and/or HTML.
          This also includes "doc" outputs.
        '';
      };

      dev.enable = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Whether to install documentation targeted at developers.
          <itemizedlist>
          <listitem><para>This includes man pages targeted at developers if <option>man.enable</option> is
                    set (this also includes "devman" outputs).</para></listitem>
          <listitem><para>This includes info pages targeted at developers if <option>info.enable</option>
                    is set (this also includes "devinfo" outputs).</para></listitem>
          <listitem><para>This includes other pages targeted at developers if <option>doc.enable</option>
                    is set (this also includes "devdoc" outputs).</para></listitem>
          </itemizedlist>
        '';
      };

    };

  };

  config = mkIf cfg.enable (mkMerge [

    (mkIf cfg.man.enable {
      environment.systemPackages = [ pkgs.man-db ];
      environment.pathsToLink = [ "/share/man" ];
      environment.extraOutputsToInstall = [ "man" ] ++ optional cfg.dev.enable "devman";
    })

    (mkIf cfg.info.enable {
      environment.systemPackages = [ pkgs.texinfoInteractive ];
      environment.pathsToLink = [ "/share/info" ];
      environment.extraOutputsToInstall = [ "info" ] ++ optional cfg.dev.enable "devinfo";
      environment.extraSetup = ''
        if [ -w $out/share/info ]; then
          shopt -s nullglob
          for i in $out/share/info/*.info $out/share/info/*.info.gz; do
              ${pkgs.texinfo}/bin/install-info $i $out/share/info/dir
          done
        fi
      '';
    })

    (mkIf cfg.doc.enable {
      # TODO(@oxij): put it here and remove from profiles?
      # environment.systemPackages = [ pkgs.w3m ]; # w3m-nox?
      environment.pathsToLink = [ "/share/doc" ];
      environment.extraOutputsToInstall = [ "doc" ] ++ optional cfg.dev.enable "devdoc";
    })

  ]);

}