# policy.py - module policy logic for Mercurial.

#

# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import os

import sys

from .pycompat import getattr

# Rules for how modules can be loaded. Values are:

#

#    c - require C extensions

#    rust+c - require Rust and C extensions

#    rust+c-allow - allow Rust and C extensions with fallback to pure Python

#                   for each

#    allow - allow pure Python implementation when C loading fails

#    cffi - required cffi versions (implemented within pure module)

#    cffi-allow - allow pure Python implementation if cffi version is missing

#    py - only load pure Python modules

#

# By default, fall back to the pure modules so the in-place build can

# run without recompiling the C extensions. This will be overridden by

# __modulepolicy__ generated by setup.py.

policy = b'allow'

_packageprefs = {

    # policy: (versioned package, pure package)

    b'c': ('cext', None),

    b'allow': ('cext', 'pure'),

    b'cffi': ('cffi', None),

    b'cffi-allow': ('cffi', 'pure'),

    b'py': (None, 'pure'),

    # For now, rust policies impact importrust only

    b'rust+c': ('cext', None),

    b'rust+c-allow': ('cext', 'pure'),

}

try:

    from . import __modulepolicy__

    policy = __modulepolicy__.modulepolicy

except ImportError:

    pass

# PyPy doesn't load C extensions.

#

# The canonical way to do this is to test platform.python_implementation().

# But we don't import platform and don't bloat for it here.

if '__pypy__' in sys.builtin_module_names:

    policy = b'cffi'

# Environment variable can always force settings.

if sys.version_info[0] >= 3:

    if 'HGMODULEPOLICY' in os.environ:

        policy = os.environ['HGMODULEPOLICY'].encode('utf-8')

else:

    policy = os.environ.get('HGMODULEPOLICY', policy)

def _importfrom(pkgname, modname):

    # from .<pkgname> import <modname> (where . is looked through this module)

    fakelocals = {}

    pkg = __import__(pkgname, globals(), fakelocals, [modname], level=1)

    try:

        fakelocals[modname] = mod = getattr(pkg, modname)

    except AttributeError:

        raise ImportError('cannot import name %s' % modname)

    # force import; fakelocals[modname] may be replaced with the real module

    getattr(mod, '__doc__', None)

    return fakelocals[modname]

# keep in sync with "version" in C modules

_cextversions = {

    ('cext', 'base85'): 1,

    ('cext', 'bdiff'): 3,

    ('cext', 'mpatch'): 1,

    ('cext', 'osutil'): 4,

}

# map import request to other package or module

_modredirects = {

    ('cext', 'charencode'): ('cext', 'parsers'),

    ('cffi', 'base85'): ('pure', 'base85'),

    ('cffi', 'charencode'): ('pure', 'charencode'),

    ('cffi', 'parsers'): ('pure', 'parsers'),

}

def _checkmod(pkgname, modname, mod):

    expected = _cextversions.get((pkgname, modname))

    actual = getattr(mod, 'version', None)

    if actual != expected:

        raise ImportError(

            'cannot import module %s.%s '

            '(expected version: %d, actual: %r)'

            % (pkgname, modname, expected, actual)

        )

def importmod(modname):

    """Import module according to policy and check API version"""

    try:

        verpkg, purepkg = _packageprefs[policy]

    except KeyError:

        raise ImportError('invalid HGMODULEPOLICY %r' % policy)

    assert verpkg or purepkg

    if verpkg:

        pn, mn = _modredirects.get((verpkg, modname), (verpkg, modname))

        try:

            mod = _importfrom(pn, mn)

            if pn == verpkg:

                _checkmod(pn, mn, mod)

            return mod

        except ImportError:

            if not purepkg:

                raise

    pn, mn = _modredirects.get((purepkg, modname), (purepkg, modname))

    return _importfrom(pn, mn)

def _isrustpermissive():

    """Assuming the policy is a Rust one, tell if it's permissive."""

    return policy.endswith(b'-allow')

def importrust(modname, member=None, default=None):

    """Import Rust module according to policy and availability.

    If policy isn't a Rust one, this returns `default`.

    If either the module or its member is not available, this returns `default`

    if policy is permissive and raises `ImportError` if not.

    """

    if not policy.startswith(b'rust'):

        return default

    try:

        mod = _importfrom('rustext', modname)

    except ImportError:

        if _isrustpermissive():

            return default

        raise

    if member is None:

        return mod

    try:

        return getattr(mod, member)

    except AttributeError:

        if _isrustpermissive():

            return default

        raise ImportError("Cannot import name %s" % member)