# Copyright (c) 2017-present, Gregory Szorc

# All rights reserved.

#

# This software may be modified and distributed under the terms

# of the BSD license. See the LICENSE file for details.

"""Python interface to the Zstandard (zstd) compression library."""

from __future__ import absolute_import, unicode_literals

# This module serves 2 roles:

#

# 1) Export the C or CFFI "backend" through a central module.

# 2) Implement additional functionality built on top of C or CFFI backend.

import os

import platform

# Some Python implementations don't support C extensions. That's why we have

# a CFFI implementation in the first place. The code here import one of our

# "backends" then re-exports the symbols from this module. For convenience,

# we support falling back to the CFFI backend if the C extension can't be

# imported. But for performance reasons, we only do this on unknown Python

# implementation. Notably, for CPython we require the C extension by default.

# Because someone will inevitably want special behavior, the behavior is

# configurable via an environment variable. A potentially better way to handle

# this is to import a special ``__importpolicy__`` module or something

# defining a variable and `setup.py` could write the file with whatever

# policy was specified at build time. Until someone needs it, we go with

# the hacky but simple environment variable approach.

_module_policy = os.environ.get('PYTHON_ZSTANDARD_IMPORT_POLICY', 'default')

if _module_policy == 'default':

    if platform.python_implementation() in ('CPython',):

        from zstd import *

        backend = 'cext'

    elif platform.python_implementation() in ('PyPy',):

        from zstd_cffi import *

        backend = 'cffi'

    else:

        try:

            from zstd import *

            backend = 'cext'

        except ImportError:

            from zstd_cffi import *

            backend = 'cffi'

elif _module_policy == 'cffi_fallback':

    try:

        from zstd import *

        backend = 'cext'

    except ImportError:

        from zstd_cffi import *

        backend = 'cffi'

elif _module_policy == 'cext':

    from zstd import *

    backend = 'cext'

elif _module_policy == 'cffi':

    from zstd_cffi import *

    backend = 'cffi'

else:

    raise ImportError('unknown module import policy: %s; use default, cffi_fallback, '

                      'cext, or cffi' % _module_policy)