{ pkgs, options, version, revision }:

with pkgs;
with pkgs.lib;

let

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

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

  # Clean up declaration sites to not refer to the NixOS source tree.
  optionsList' = flip map optionsList (opt: opt // {
    declarations = map (fn: stripPrefix fn) opt.declarations;
  }
  // optionalAttrs (opt ? example) { example = substFunction opt.example; }
  // optionalAttrs (opt ? default) { default = substFunction opt.default; });

  prefix = toString ../../..;

  stripPrefix = fn:
    if substring 0 (stringLength prefix) fn == prefix then
      substring (stringLength prefix + 1) 1000 fn
    else
      fn;

  # Convert the list of options into an XML file and a JSON file.  The builtin
  # unsafeDiscardStringContext is used to prevent the realisation of the store
  # paths which are used in options definitions.
  optionsXML = builtins.toFile "options.xml" (builtins.unsafeDiscardStringContext (builtins.toXML optionsList'));
  optionsJSON = builtins.toFile "options.json" (builtins.unsafeDiscardStringContext (builtins.toJSON optionsList'));

  # Tools-friendly version of the list of NixOS options.
  options' = stdenv.mkDerivation {
    name = "options";

    buildCommand = ''
      # Export list of options in different format.
      dst=$out/share/doc/nixos
      mkdir -p $dst

      cp ${optionsJSON} $dst/options.json
      cp ${optionsXML} $dst/options.xml

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

    meta.description = "List of NixOS options in various formats.";
  };

  optionsDocBook = runCommand "options-db.xml" {} ''
    optionsXML=${options'}/doc/share/nixos/options.xml
    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
    ${libxslt}/bin/xsltproc \
      --stringparam revision '${revision}' \
      -o $out ${./options-to-docbook.xsl} $optionsXML
  '';

  sources = sourceFilesBySuffices ./. [".xml"];

  copySources =
    ''
      cp -prd $sources/* . # */
      chmod -R u+w .
      cp ${../../modules/services/databases/postgresql.xml} configuration/postgresql.xml
      ln -s ${optionsDocBook} options-db.xml
      echo "${version}" > version
    '';

in rec {

  # Tools-friendly version of the list of NixOS options.
  options = options';

  # Generate the NixOS manual.
  manual = stdenv.mkDerivation {
    name = "nixos-manual";

    inherit sources;

    buildInputs = [ libxml2 libxslt ];

    buildCommand = ''
      ${copySources}

      # Check the validity of the manual sources.
      xmllint --noout --nonet --xinclude --noxincludenode \
        --relaxng ${docbook5}/xml/rng/docbook/docbook.rng \
        manual.xml

      # Generate the HTML manual.
      dst=$out/share/doc/nixos
      mkdir -p $dst
      xsltproc \
        --param section.autolabel 1 \
        --param section.label.includes.component.label 1 \
        --stringparam html.stylesheet style.css \
        --param xref.with.number.and.title 1 \
        --param toc.section.depth 3 \
        --stringparam admon.style "" \
        --stringparam callout.graphics.extension .gif \
        --param chunk.section.depth 0 \
        --param chunk.first.sections 1 \
        --param use.id.as.filename 1 \
        --stringparam generate.toc "book toc chapter toc appendix toc" \
        --nonet --xinclude --output $dst/ \
        ${docbook5_xsl}/xml/xsl/docbook/xhtml/chunkfast.xsl ./manual.xml

      mkdir -p $dst/images/callouts
      cp ${docbook5_xsl}/xml/xsl/docbook/images/callouts/*.gif $dst/images/callouts/

      cp ${./style.css} $dst/style.css

      mkdir -p $out/nix-support
      echo "nix-build out $out" >> $out/nix-support/hydra-build-products
      echo "doc manual $dst manual.html" >> $out/nix-support/hydra-build-products
    ''; # */

    meta.description = "The NixOS manual in HTML format";
  };

  manualPDF = stdenv.mkDerivation {
    name = "nixos-manual-pdf";

    inherit sources;

    buildInputs = [ libxml2 libxslt dblatex tetex ];

    buildCommand = ''
      # TeX needs a writable font cache.
      export VARTEXFONTS=$TMPDIR/texfonts

      ${copySources}

      dst=$out/share/doc/nixos
      mkdir -p $dst
      xmllint --xinclude manual.xml | dblatex -o $dst/manual.pdf - \
        -P doc.collab.show=0 \
        -P latex.output.revhistory=0

      mkdir -p $out/nix-support
      echo "doc-pdf manual $dst/manual.pdf" >> $out/nix-support/hydra-build-products
    ''; # */
  };

  # Generate the NixOS manpages.
  manpages = stdenv.mkDerivation {
    name = "nixos-manpages";

    inherit sources;

    buildInputs = [ libxml2 libxslt ];

    buildCommand = ''
      ${copySources}

      # Check the validity of the manual sources.
      xmllint --noout --nonet --xinclude --noxincludenode \
        --relaxng ${docbook5}/xml/rng/docbook/docbook.rng \
        ./man-pages.xml

      # Generate manpages.
      mkdir -p $out/share/man
      xsltproc --nonet --xinclude \
        --param man.output.in.separate.dir 1 \
        --param man.output.base.dir "'$out/share/man/'" \
        --param man.endnotes.are.numbered 0 \
        ${docbook5_xsl}/xml/xsl/docbook/manpages/docbook.xsl \
        ./man-pages.xml
    '';
  };

}