{fetchurl, writeScript, ruby, ncurses, sqlite, libxml2, libxslt, libffi, zlib,
  libuuid}:
gems:

let
  patchUsrBinEnv = writeScript "path-usr-bin-env" ''
    #!/bin/sh
    set -x
    echo "==================="
    find "$1" -type f -name "*.rb" | xargs sed -i "s@/usr/bin/env@$(type -p env)@g"
    find "$1" -type f -name "*.mk" | xargs sed -i "s@/usr/bin/env@$(type -p env)@g"
  '';
in
{
  sup = { buildInputs = [ gems.ncursesw ]; };
  sqlite3 = { propagatedBuildInputs = [ sqlite ]; };
  rails = { gemFlags = "--no-ri --no-rdoc"; };
  ncurses = { propagatedBuildInputs = [ ncurses ]; };
  ncursesw = { propagatedBuildInputs = [ ncurses ]; };
  nokogiri = {
    buildFlags=["--with-xml2-dir=${libxml2} --with-xml2-include=${libxml2}/include/libxml2"
                "--with-xslt-dir=${libxslt}" ];
  };

  ffi = {
    postUnpack = "onetuh";
    buildFlags=["--with-ffi-dir=${libffi}"];
    NIX_POST_EXTRACT_FILES_HOOK = patchUsrBinEnv;
  };

  xrefresh_server =
  let patch = fetchurl {
      url = "http://mawercer.de/~nix/xrefresh.diff.gz";
      sha256 = "1f7bnmn1pgkmkml0ms15m5lx880hq2sxy7vsddb3sbzm7n1yyicq";
    };
  in {
    propagatedBuildInputs = [ gems.rb_inotify ];

    # monitor implementation for Linux
    postInstall = ''
      cd $out/${ruby.gemPath}/gems/*
      zcat ${patch} | patch -p 1
    '';
  };

  xapian_full = {
    buildInputs = [ gems.rake zlib libuuid ];
    gemFlags = "--no-rdoc --no-ri";
  };
}