# 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."""

# 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 .cffi import *

        backend = "cffi"

    else:

        try:

            from zstd import *

            backend = "cext"

        except ImportError:

            from .cffi import *

            backend = "cffi"

elif _module_policy == "cffi_fallback":

    try:

        from zstd import *

        backend = "cext"

    except ImportError:

        from .cffi import *

        backend = "cffi"

elif _module_policy == "cext":

    from zstd import *

    backend = "cext"

elif _module_policy == "cffi":

    from .cffi import *

    backend = "cffi"

else:

    raise ImportError(

        "unknown module import policy: %s; use default, cffi_fallback, "

        "cext, or cffi" % _module_policy

    )

# Keep this in sync with python-zstandard.h.

__version__ = "0.13.0"