# demandimport.py - global demand-loading of modules for Mercurial

#

# Copyright 2006, 2007 Matt Mackall <mpm@selenic.com>

#

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

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

'''

demandimport - automatic demandloading of modules

To enable this module, do:

  import demandimport; demandimport.enable()

Imports of the following forms will be demand-loaded:

  import a, b.c

  import a.b as c

  from a import b,c # a will be loaded immediately

These imports will not be delayed:

  from a import *

  b = __import__(a)

'''

import os, sys

from contextlib import contextmanager

_origimport = __import__

nothing = object()

try:

    # Python 3 doesn't have relative imports nor level -1.

    level = -1

    if sys.version_info[0] >= 3:

        level = 0

    _origimport(builtins.__name__, {}, {}, None, level)

except TypeError: # no level argument

    def _import(name, globals, locals, fromlist, level):

        "call _origimport with no level argument"

        return _origimport(name, globals, locals, fromlist)

else:

    _import = _origimport

def _hgextimport(importfunc, name, globals, *args):

    try:

        return importfunc(name, globals, *args)

    except ImportError:

        if not globals:

            raise

        # extensions are loaded with "hgext_" prefix

        hgextname = 'hgext_%s' % name

        nameroot = hgextname.split('.', 1)[0]

        contextroot = globals.get('__name__', '').split('.', 1)[0]

        if nameroot != contextroot:

            raise

        # retry to import with "hgext_" prefix

        return importfunc(hgextname, globals, *args)

class _demandmod(object):

    """module demand-loader and proxy"""

    def __init__(self, name, globals, locals, level=level):

        if '.' in name:

            head, rest = name.split('.', 1)

            after = [rest]

        else:

            head = name

            after = []

        object.__setattr__(self, "_data",

                           (head, globals, locals, after, level))

        object.__setattr__(self, "_module", None)

    def _extend(self, name):

        """add to the list of submodules to load"""

        self._data[3].append(name)

    def _load(self):

        if not self._module:

            head, globals, locals, after, level = self._data

            mod = _hgextimport(_import, head, globals, locals, None, level)

            # load submodules

            def subload(mod, p):

                h, t = p, None

                if '.' in p:

                    h, t = p.split('.', 1)

                if getattr(mod, h, nothing) is nothing:

                    setattr(mod, h, _demandmod(p, mod.__dict__, mod.__dict__))

                elif t:

                    subload(getattr(mod, h), t)

            for x in after:

                subload(mod, x)

            # are we in the locals dictionary still?

            if locals and locals.get(head) == self:

                locals[head] = mod

            object.__setattr__(self, "_module", mod)

    def __repr__(self):

        if self._module:

            return "<proxied module '%s'>" % self._data[0]

        return "<unloaded module '%s'>" % self._data[0]

    def __call__(self, *args, **kwargs):

        raise TypeError("%s object is not callable" % repr(self))

    def __getattribute__(self, attr):

        if attr in ('_data', '_extend', '_load', '_module'):

            return object.__getattribute__(self, attr)

        self._load()

        return getattr(self._module, attr)

    def __setattr__(self, attr, val):

        self._load()

        setattr(self._module, attr, val)

def _demandimport(name, globals=None, locals=None, fromlist=None, level=level):

    if not locals or name in ignore or fromlist == ('*',):

        # these cases we can't really delay

        return _hgextimport(_import, name, globals, locals, fromlist, level)

    elif not fromlist:

        # import a [as b]

        if '.' in name: # a.b

            base, rest = name.split('.', 1)

            # email.__init__ loading email.mime

            if globals and globals.get('__name__', None) == base:

                return _import(name, globals, locals, fromlist, level)

            # if a is already demand-loaded, add b to its submodule list

            if base in locals:

                if isinstance(locals[base], _demandmod):

                    locals[base]._extend(rest)

                return locals[base]

        return _demandmod(name, globals, locals, level)

    else:

        if level != -1:

            # from . import b,c,d or from .a import b,c,d

            return _origimport(name, globals, locals, fromlist, level)

        # from a import b,c,d

        mod = _hgextimport(_origimport, name, globals, locals)

        # recurse down the module chain

        for comp in name.split('.')[1:]:

            if getattr(mod, comp, nothing) is nothing:

                setattr(mod, comp, _demandmod(comp, mod.__dict__, mod.__dict__))

            mod = getattr(mod, comp)

        for x in fromlist:

            # set requested submodules for demand load

            if getattr(mod, x, nothing) is nothing:

                setattr(mod, x, _demandmod(x, mod.__dict__, locals))

        return mod

ignore = [

    '_hashlib',

    '_xmlplus',

    'fcntl',

    'win32com.gen_py',

    '_winreg', # 2.7 mimetypes needs immediate ImportError

    'pythoncom',

    # imported by tarfile, not available under Windows

    'pwd',

    'grp',

    # imported by profile, itself imported by hotshot.stats,

    # not available under Windows

    'resource',

    # this trips up many extension authors

    'gtk',

    # setuptools' pkg_resources.py expects "from __main__ import x" to

    # raise ImportError if x not defined

    '__main__',

    '_ssl', # conditional imports in the stdlib, issue1964

    'rfc822',

    'mimetools',

    # setuptools 8 expects this module to explode early when not on windows

    'distutils.msvc9compiler'

    ]

def isenabled():

    return builtins.__import__ == _demandimport

def enable():

    "enable global demand-loading of modules"

    if os.environ.get('HGDEMANDIMPORT') != 'disable':

        builtins.__import__ = _demandimport

def disable():

    "disable global demand-loading of modules"

    builtins.__import__ = _origimport

@contextmanager

def deactivated():

    "context manager for disabling demandimport in 'with' blocks"

    demandenabled = isenabled()

    if demandenabled:

        disable()

    try:

        yield

    finally:

        if demandenabled:

            enable()