# 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)

'''

from __future__ import absolute_import

import contextlib

import os

import sys

# __builtin__ in Python 2, builtins in Python 3.

try:

    import __builtin__ as builtins

except ImportError:

    import builtins

contextmanager = contextlib.contextmanager

_origimport = __import__

nothing = object()

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

level = -1

if sys.version_info[0] >= 3:

    level = 0

_import = _origimport

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

    try:

        return importfunc(name, globals, *args, **kwargs)

    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, **kwargs)

class _demandmod(object):

    """module demand-loader and proxy

    Specify 1 as 'level' argument at construction, to import module

    relatively.

    """

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

        if '.' in name:

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

            after = [rest]

        else:

            head = name

            after = []

        object.__setattr__(self, r"_data",

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

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

    def _extend(self, name):

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

        self._data[3].append(name)

    def _addref(self, name):

        """Record that the named module ``name`` imports this module.

        References to this proxy class having the name of this module will be

        replaced at module load time. We assume the symbol inside the importing

        module is identical to the "head" name of this module. We don't

        actually know if "as X" syntax is being used to change the symbol name

        because this information isn't exposed to __import__.

        """

        self._data[5].add(name)

    def _load(self):

        if not self._module:

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

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

            if mod is self:

                # In this case, _hgextimport() above should imply

                # _demandimport(). Otherwise, _hgextimport() never

                # returns _demandmod. This isn't intentional behavior,

                # in fact. (see also issue5304 for detail)

                #

                # If self._module is already bound at this point, self

                # should be already _load()-ed while _hgextimport().

                # Otherwise, there is no way to import actual module

                # as expected, because (re-)invoking _hgextimport()

                # should cause same result.

                # This is reason why _load() returns without any more

                # setup but assumes self to be already bound.

                mod = self._module

                assert mod and mod is not self, "%s, %s" % (self, mod)

                return

            # 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__,

                                               level=1))

                elif t:

                    subload(getattr(mod, h), t)

            for x in after:

                subload(mod, x)

            # Replace references to this proxy instance with the actual module.

                locals[head] = mod

            for modname in modrefs:

                modref = sys.modules.get(modname, None)

                    setattr(modref, head, mod)

            object.__setattr__(self, r"_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', '_addref'):

            return object.__getattribute__(self, attr)

        self._load()

        return getattr(self._module, attr)

    def __setattr__(self, attr, val):

        self._load()

        setattr(self._module, attr, val)

_pypy = '__pypy__' in sys.builtin_module_names

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

    if locals is None 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:

        # There is a fromlist.

        # from a import b,c,d

        # from . import b,c,d

        # from .a import b,c,d

        # level == -1: relative and absolute attempted (Python 2 only).

        # level >= 0: absolute only (Python 2 w/ absolute_import and Python 3).

        # The modern Mercurial convention is to use absolute_import everywhere,

        # so modern Mercurial code will have level >= 0.

        # The name of the module the import statement is located in.

        globalname = globals.get('__name__')

        def processfromitem(mod, attr):

            """Process an imported symbol in the import statement.

            If the symbol doesn't exist in the parent module, and if the

            parent module is a package, it must be a module. We set missing

            modules up as _demandmod instances.

            """

            symbol = getattr(mod, attr, nothing)

            nonpkg = getattr(mod, '__path__', nothing) is nothing

            if symbol is nothing:

                if nonpkg:

                    # do not try relative import, which would raise ValueError,

                    # and leave unknown attribute as the default __import__()

                    # would do. the missing attribute will be detected later

                    # while processing the import statement.

                    return

                mn = '%s.%s' % (mod.__name__, attr)

                if mn in ignore:

                    importfunc = _origimport

                else:

                    importfunc = _demandmod

                symbol = importfunc(attr, mod.__dict__, locals, level=1)

                setattr(mod, attr, symbol)

            # Record the importing module references this symbol so we can

            # replace the symbol with the actual module instance at load

            # time.

            if globalname and isinstance(symbol, _demandmod):

                symbol._addref(globalname)

        def chainmodules(rootmod, modname):

            # recurse down the module chain, and return the leaf module

            mod = rootmod

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

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

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

                                                  mod.__dict__, level=1))

                mod = getattr(mod, comp)

            return mod

        if level >= 0:

            if name:

                # "from a import b" or "from .a import b" style

                rootmod = _hgextimport(_origimport, name, globals, locals,

                                       level=level)

                mod = chainmodules(rootmod, name)

            elif _pypy:

                # PyPy's __import__ throws an exception if invoked

                # with an empty name and no fromlist.  Recreate the

                # desired behaviour by hand.

                mn = globalname

                mod = sys.modules[mn]

                if getattr(mod, '__path__', nothing) is nothing:

                    mn = mn.rsplit('.', 1)[0]

                    mod = sys.modules[mn]

                if level > 1:

                    mn = mn.rsplit('.', level - 1)[0]

                    mod = sys.modules[mn]

            else:

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

                                   level=level)

            for x in fromlist:

                processfromitem(mod, x)

            return mod

        # But, we still need to support lazy loading of standard library and 3rd

        # party modules. So handle level == -1.

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

        mod = chainmodules(mod, name)

        for x in fromlist:

            processfromitem(mod, x)

        return mod

ignore = []

def init(ignorelist):

    global ignore

    ignore = ignorelist

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()