# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
# Licensed under the Apache License, Version 2.0 (see LICENSE).

import os
from contextlib import contextmanager

from pants.base.build_environment import get_pants_cachedir
from pants.util.contextutil import environment_as, temporary_dir
from pants.util.dirutil import safe_mkdir_for


@contextmanager
def setup_pexrc_with_pex_python_path(interpreter_paths):
    """A helper function for writing interpreter paths to a PEX_PYTHON_PATH variable in a .pexrc
    file.

    NB: Mutates HOME and XDG_CACHE_HOME to ensure a `~/.pexrc` that won't trample any existing file
    and will also be found.

    :param list interpreter_paths: a list of paths to interpreter binaries to include on
                                   PEX_PYTHON_PATH.
    """
    cache_dir = get_pants_cachedir()
    with temporary_dir() as home:
        xdg_cache_home = os.path.join(home, ".cache")
        with environment_as(HOME=home, XDG_CACHE_HOME=xdg_cache_home):
            target = os.path.join(xdg_cache_home, os.path.basename(cache_dir))
            safe_mkdir_for(target)
            os.symlink(cache_dir, target)

            with open(os.path.join(home, ".pexrc"), "w") as pexrc:
                pexrc.write(f"PEX_PYTHON_PATH={':'.join(interpreter_paths)}")

            yield