# -*- coding: utf-8 -*-
#
# File: portato/backend/__init__.py
# This file is part of the Portato-Project, a graphical portage-frontend.
#
# Copyright (C) 2006-2009 René 'Necoro' Neumann
# This is free software.  You may redistribute copies of it under the terms of
# the GNU General Public License version 2.
# There is NO WARRANTY, to the extent permitted by law.
#
# Written by René 'Necoro' Neumann <necoro@necoro.net>

from __future__ import absolute_import

from ..helper import debug
from .system_interface import SystemInterface
from .exceptions import BlockedException, PackageNotFoundException, DependencyCalcError, InvalidSystemError

SYSTEM = "portage" # the name of the current system
_sys = None # the SystemInterface-instance

class _Package (object):
    """Wrapping class from which L{portato.backend.Package} inherits. This is used by the flags module to check
    whether an object is a package. It cannot use the normal Package class as this results in cyclic dependencies."""

    def __init__ (self):
        raise TypeError, "Calling __init__ on portato.backend._Package objects is not allowed."

class SystemWrapper (SystemInterface):
    """This is a wrapper to the different system interfaces, allowing the direct import via C{from portato.backend import system}.
    With this wrapper a change of the system is propagated to all imports."""
    
    def __getattribute__ (self, name):
        """Just pass all attribute accesses directly to _sys."""
        return getattr(_sys, name)

def set_system (new_sys):
    """Sets the current system to a new one.

    @param new_sys: the name of the system to take
    @type new_sys: string"""

    global SYSTEM
    if new_sys != SYSTEM:
        SYSTEM = new_sys
        load_system()

def load_system ():
    """Loads the current chosen system.

    @raises InvalidSystemError: if an inappropriate system is set"""
    
    global _sys

    if SYSTEM == "portage":
        debug("Setting Portage System")
        from .portage import PortageSystem
        _sys = PortageSystem ()
    else:
        raise InvalidSystemError, SYSTEM

system = SystemWrapper()

def is_package(what):
    return isinstance(what, _Package)

load_system()