#------------------------------------------------------------------------------
# Copyright (c) 2007, Riverbank Computing Limited
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in enthought/LICENSE.txt and may be redistributed only
# under the conditions described in the aforementioned license.  The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
#------------------------------------------------------------------------------

# Standard library imports.
import os
import sys

# Enthought library imports.
from traits.etsconfig.api import ETSConfig


# This is set to the root part of the module path for the selected backend.
_toolkit_backend = None


def _init_toolkit():
    """ Initialise the current toolkit. """

    def import_toolkit(tk):
        try:
            # Try and import the toolkit's pyface backend init module.
            be = 'pyface.ui.%s.' % tk
            __import__(be + 'init')
        except:
            raise
        return be

    # Get the toolkit.
    if ETSConfig.toolkit:
        be = import_toolkit(ETSConfig.toolkit)
    else:
        # Toolkits to check for if none is explicitly specified.
        import warnings
        warnings.warn("Default toolkit will change to 'qt4' in PyFace 5.0",
                      DeprecationWarning)

        known_toolkits = ('wx', 'qt4', 'null')

        for tk in known_toolkits:
            try:
                be = import_toolkit(tk)

                # In case we have just decided on a toolkit, tell everybody else.
                ETSConfig.toolkit = tk
                break
            except (SystemExit, ImportError):
                import traceback
                print >>sys.stderr, ('Warning: Unable to import the %s backend '
                    'for pyface due to traceback: %s\n') % (tk,
                    traceback.format_exc().strip().replace('\n', '\n\t'))

        else:
            # Try to import the null toolkit but don't set the ETSConfig toolkit
            try:
                be = import_toolkit('null')
                print >>sys.stderr, ("Info: Unable to import any backend (%s) "
                    "for pyface; using the 'null' toolkit instead.\n") % ", ".join(known_toolkits)
            except:
                raise ImportError("Unable to import a pyface backend for any "
                    "of the %s toolkits" % ", ".join(known_toolkits))


    # Save the imported toolkit module.
    global _toolkit_backend
    _toolkit_backend = be


# Do this once then disappear.
_init_toolkit()
del _init_toolkit


def toolkit_object(name):
    """ Return the toolkit specific object with the given name.  The name
    consists of the relative module path and the object name separated by a
    colon.
    """

    mname, oname = name.split(':')
    be_mname = _toolkit_backend + mname

    class Unimplemented(object):
        """ This is returned if an object isn't implemented by the selected
        toolkit.  It raises an exception if it is ever instantiated.
        """

        def __init__(self, *args, **kwargs):
            raise NotImplementedError("the %s pyface backend doesn't implement %s" % (ETSConfig.toolkit, oname))

    be_obj = Unimplemented

    try:
        __import__(be_mname)

        try:
            be_obj = getattr(sys.modules[be_mname], oname)
        except AttributeError:
            pass
    except ImportError as exc:
        # is the error while trying to import be_mname or not?
        if not exc.message.endswith(mname):
            # something else went wrong - let the exception be raised
            raise

        # Ignore *ANY* errors unless a debug ENV variable is set.
        if 'ETS_DEBUG' in os.environ:

            # Attempt to only skip errors in importing the backend modules.
            # The idea here is that this only happens when the last entry in
            # the traceback's stack frame mentions the toolkit in question.
            import traceback
            frames = traceback.extract_tb(sys.exc_traceback)
            filename, lineno, function, text = frames[-1]
            if not _toolkit_backend in filename:
                raise

    return be_obj
