/* Generate JSON, XML and DocBook documentation for given NixOS options.

   Minimal example:

    { pkgs,  }:

    let
      eval = import (pkgs.path + "/nixos/lib/eval-config.nix") {
        baseModules = [
          ../module.nix
        ];
        modules = [];
      };
    in pkgs.nixosOptionsDoc {
      options = eval.options;
    }

*/
{ pkgs
, lib
, options
, transformOptions ? lib.id  # function for additional tranformations of the options
, revision ? "" # Specify revision for the options
}:

let
  # Replace functions by the string <function>
  substFunction = x:
    if builtins.isAttrs x then lib.mapAttrs (name: substFunction) x
    else if builtins.isList x then map substFunction x
    else if lib.isFunction x then "<function>"
    else x;

  optionsListDesc = lib.flip map optionsListVisible
   (opt: transformOptions opt
    // lib.optionalAttrs (opt ? example) { example = substFunction opt.example; }
    // lib.optionalAttrs (opt ? default) { default = substFunction opt.default; }
    // lib.optionalAttrs (opt ? type) { type = substFunction opt.type; }
    // lib.optionalAttrs (opt ? relatedPackages && opt.relatedPackages != []) { relatedPackages = genRelatedPackages opt.relatedPackages opt.name; }
   );

  # Generate DocBook documentation for a list of packages. This is
  # what `relatedPackages` option of `mkOption` from
  # ../../../lib/options.nix influences.
  #
  # Each element of `relatedPackages` can be either
  # - a string:  that will be interpreted as an attribute name from `pkgs`,
  # - a list:    that will be interpreted as an attribute path from `pkgs`,
  # - an attrset: that can specify `name`, `path`, `package`, `comment`
  #   (either of `name`, `path` is required, the rest are optional).
  genRelatedPackages = packages: optName:
    let
      unpack = p: if lib.isString p then { name = p; }
                  else if lib.isList p then { path = p; }
                  else p;
      describe = args:
        let
          title = args.title or null;
          name = args.name or (lib.concatStringsSep "." args.path);
          path = args.path or [ args.name ];
          package = args.package or (lib.attrByPath path (throw "Invalid package attribute path `${toString path}' found while evaluating `relatedPackages' of option `${optName}'") pkgs);
        in "<listitem>"
        + "<para><literal>${lib.optionalString (title != null) "${title} aka "}pkgs.${name} (${package.meta.name})</literal>"
        + lib.optionalString (!package.meta.available) " <emphasis>[UNAVAILABLE]</emphasis>"
        + ": ${package.meta.description or "???"}.</para>"
        + lib.optionalString (args ? comment) "\n<para>${args.comment}</para>"
        # Lots of `longDescription's break DocBook, so we just wrap them into <programlisting>
        + lib.optionalString (package.meta ? longDescription) "\n<programlisting>${package.meta.longDescription}</programlisting>"
        + "</listitem>";
    in "<itemizedlist>${lib.concatStringsSep "\n" (map (p: describe (unpack p)) packages)}</itemizedlist>";

  # Custom "less" that pushes up all the things ending in ".enable*"
  # and ".package*"
  optionLess = a: b:
    let
      ise = lib.hasPrefix "enable";
      isp = lib.hasPrefix "package";
      cmp = lib.splitByAndCompare ise lib.compare
                                 (lib.splitByAndCompare isp lib.compare lib.compare);
    in lib.compareLists cmp a.loc b.loc < 0;

  # Remove invisible and internal options.
  optionsListVisible = lib.filter (opt: opt.visible && !opt.internal) (lib.optionAttrSetToDocList options);

  # Customly sort option list for the man page.
  # Always ensure that the sort order matches sortXML.py!
  optionsList = lib.sort optionLess optionsListDesc;

  # Convert the list of options into an XML file.
  # This file is *not* sorted sorted to save on eval time, since the docbook XML
  # and the manpage depend on it and thus we evaluate this on every system rebuild.
  optionsXML = builtins.toFile "options.xml" (builtins.toXML optionsListDesc);

  optionsNix = builtins.listToAttrs (map (o: { name = o.name; value = removeAttrs o ["name" "visible" "internal"]; }) optionsList);

  # TODO: declarations: link to github
  singleAsciiDoc = name: value: ''
    == ${name}

    ${value.description}

    [discrete]
    === details

    Type:: ${value.type}
    ${ if lib.hasAttr "default" value
       then ''
        Default::
        +
        ----
        ${builtins.toJSON value.default}
        ----
      ''
      else "No Default:: {blank}"
    }
    ${ if value.readOnly
       then "Read Only:: {blank}"
      else ""
    }
    ${ if lib.hasAttr "example" value
       then ''
        Example::
        +
        ----
        ${builtins.toJSON value.example}
        ----
      ''
      else "No Example:: {blank}"
    }
  '';

  singleMDDoc = name: value: ''
    ## ${lib.escape [ "<" ">" ] name}
    ${value.description}

    ${lib.optionalString (value ? type) ''
      *_Type_*:
      ${value.type}
    ''}

    ${lib.optionalString (value ? default) ''
      *_Default_*
      ```
      ${builtins.toJSON value.default}
      ```
    ''}

    ${lib.optionalString (value ? example) ''
      *_Example_*
      ```
      ${builtins.toJSON value.example}
      ```
    ''}
  '';

in {
  inherit optionsNix;

  optionsAsciiDoc = lib.concatStringsSep "\n" (lib.mapAttrsToList singleAsciiDoc optionsNix);

  optionsMDDoc = lib.concatStringsSep "\n" (lib.mapAttrsToList singleMDDoc optionsNix);

  optionsJSON = pkgs.runCommand "options.json"
    { meta.description = "List of NixOS options in JSON format";
      buildInputs = [ pkgs.brotli ];
    }
    ''
      # Export list of options in different format.
      dst=$out/share/doc/nixos
      mkdir -p $dst

      cp ${builtins.toFile "options.json" (builtins.unsafeDiscardStringContext (builtins.toJSON optionsNix))} $dst/options.json

      brotli -9 < $dst/options.json > $dst/options.json.br

      mkdir -p $out/nix-support
      echo "file json $dst/options.json" >> $out/nix-support/hydra-build-products
      echo "file json-br $dst/options.json.br" >> $out/nix-support/hydra-build-products
    ''; # */

  optionsDocBook = pkgs.runCommand "options-docbook.xml" {} ''
    optionsXML=${optionsXML}
    if grep /nixpkgs/nixos/modules $optionsXML; then
      echo "The manual appears to depend on the location of Nixpkgs, which is bad"
      echo "since this prevents sharing via the NixOS channel.  This is typically"
      echo "caused by an option default that refers to a relative path (see above"
      echo "for hints about the offending path)."
      exit 1
    fi

    ${pkgs.python3Minimal}/bin/python ${./sortXML.py} $optionsXML sorted.xml
    ${pkgs.libxslt.bin}/bin/xsltproc \
      --stringparam revision '${revision}' \
      -o intermediate.xml ${./options-to-docbook.xsl} sorted.xml
    ${pkgs.libxslt.bin}/bin/xsltproc \
      -o "$out" ${./postprocess-option-descriptions.xsl} intermediate.xml
  '';
}