/* This function provides a generic Python package builder.  It is
   intended to work with packages that use `setuptools'
   (http://pypi.python.org/pypi/setuptools/), which represents a large
   number of Python packages nowadays.  */

{ python, setuptools, wrapPython, lib, site, offlineDistutils, unzip }:

{ name, namePrefix ? "python-"

, buildInputs ? []

, # List of packages that should be added to the PYTHONPATH
  # environment variable in programs built by this function.  Packages
  # in the standard `propagatedBuildInputs' variable are also added.
  # The difference is that `pythonPath' is not propagated to the user
  # environment.  This is preferrable for programs because it doesn't
  # pollute the user environment.
  pythonPath ? []

  # distutils registers dependencies in .pth (good) but also creates
  # console_scripts for dependencies in bin/ (bad). easy_install
  # creates no scripts for dependencies (good) but does not register
  # them in pth neither (bad) - the combination gives us a pth with
  # dependencies and scripts only for the package we are currently
  # installing.
, installCommand ?
    ''
      # install the current package with easy_install.pth including dependencies
      python setup.py install --prefix="$out"

      # plain distutils knows no dependencies
      eapth="$out"/lib/${python.libPrefix}/site-packages/easy-install.pth
      if [ -e "$eapth" ]; then
          # remove console_scripts again, because they were created for deps, too
          rm -Rf "$out"/bin

          # run easy_install to generate scripts for the current package,
          # it won't reinstall
          easy_install --prefix="$out" .

          # move colliding easy_install.pth to specifically named one
          mv "$eapth" $(dirname "$eapth")/${name}.pth
      fi

      # These cause collisions and our output is not a site anyway
      # If you need a site, install python-site
      rm -f "$out/lib/${python.libPrefix}/site-packages/"site.py*

      # If setuptools is a dependency, it is included in $(name}.pth
      rm -f "$out/lib/${python.libPrefix}/site-packages/setuptools.pth"
    ''
    
, buildPhase ? "true"

, doCheck ? true

, checkPhase ?
    ''
      runHook preCheck
      python setup.py test
      runHook postCheck
    ''

, postInstall ? ""

, ... } @ attrs:

# Keep extra attributes from ATTR, e.g., `patchPhase', etc.
python.stdenv.mkDerivation (attrs // {
  inherit doCheck buildPhase checkPhase;

  name = namePrefix + name;

  buildInputs = [ python wrapPython setuptools unzip ] ++ buildInputs ++ pythonPath;

  preConfigure = ''
    # do not allow distutils to make downloads, whatever install command is used
    export PYTHONPATH="${setuptools}/lib/${python.libPrefix}:$PYTHONPATH"
    export PYTHONPATH="${offlineDistutils}/lib/${python.libPrefix}:$PYTHONPATH"

    # enable pth files for dependencies
    export PYTHONPATH="${site}/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
  '';

  # XXX: I think setuptools is not needed here
  pythonPath = [ setuptools site ] ++ pythonPath;

  # XXX: Should we run `easy_install --always-unzip'?  It doesn't seem
  # to have a noticeable impact on small scripts.
  installPhase = ''
    mkdir -p "$out/lib/${python.libPrefix}/site-packages"

    echo "installing \`${name}' with \`easy_install'..."
    export PYTHONPATH="$out/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
    ${installCommand}

    ${postInstall}
  '';

  postFixup =
    ''
      wrapPythonPrograms
    
      # If a user installs a Python package, she probably also wants its
      # dependencies in the user environment (since Python modules don't
      # have something like an RPATH, so the only way to find the
      # dependencies is to have them in the PYTHONPATH variable).
      #
      # XXX: this is not needed for things to work (pth pulls in deps)
      # but would be nice to have anyway - However, python deps end up
      # in propagated-build-native-inputs
      if test -e $out/nix-support/propagated-build-inputs; then
          ln -s $out/nix-support/propagated-build-inputs $out/nix-support/propagated-user-env-packages
      fi
    '';
})