# -*- coding: utf-8 -*-
""" PolymorphicModel Meta Class
    Please see README.rst or DOCS.rst or http://bserve.webhop.org/wiki/django_polymorphic
"""

import sys
import inspect

from django.db import models
from django.db.models.base import ModelBase

from manager import PolymorphicManager
from query import PolymorphicQuerySet

# PolymorphicQuerySet Q objects (and filter()) support these additional key words.
# These are forbidden as field names (a descriptive exception is raised)
POLYMORPHIC_SPECIAL_Q_KWORDS = [ 'instance_of', 'not_instance_of']


###################################################################################
### PolymorphicModel meta class

class PolymorphicModelBase(ModelBase):
    """
    Manager inheritance is a pretty complex topic which may need
    more thought regarding how this should be handled for polymorphic
    models.

    In any case, we probably should propagate 'objects' and 'base_objects'
    from PolymorphicModel to every subclass. We also want to somehow
    inherit/propagate _default_manager as well, as it needs to be polymorphic.

    The current implementation below is an experiment to solve this
    problem with a very simplistic approach: We unconditionally
    inherit/propagate any and all managers (using _copy_to_model),
    as long as they are defined on polymorphic models
    (the others are left alone).

    Like Django ModelBase, we special-case _default_manager:
    if there are any user-defined managers, it is set to the first of these.

    We also require that _default_manager as well as any user defined
    polymorphic managers produce querysets that are derived from
    PolymorphicQuerySet.
    """

    def __new__(self, model_name, bases, attrs):
        #print; print '###', model_name, '- bases:', bases

        # create new model
        new_class = self.call_superclass_new_method(model_name, bases, attrs)

        # check if the model fields are all allowed
        self.validate_model_fields(new_class)

        # create list of all managers to be inherited from the base classes
        inherited_managers = new_class.get_inherited_managers(attrs)

        # add the managers to the new model
        for source_name, mgr_name, manager in inherited_managers:
            #print '** add inherited manager from model %s, manager %s, %s' % (source_name, mgr_name, manager.__class__.__name__)
            new_manager = manager._copy_to_model(new_class)
            new_class.add_to_class(mgr_name, new_manager)

        # get first user defined manager; if there is one, make it the _default_manager
        user_manager = self.get_first_user_defined_manager(model_name, attrs)
        if user_manager:
            def_mgr = user_manager._copy_to_model(new_class)
            #print '## add default manager', type(def_mgr)
            new_class.add_to_class('_default_manager', def_mgr)
            new_class._default_manager._inherited = False   # the default mgr was defined by the user, not inherited

        # validate resulting default manager
        self.validate_model_manager(new_class._default_manager, model_name, '_default_manager')

        # for __init__ function of this class (monkeypatching inheritance accessors)
        new_class.polymorphic_super_sub_accessors_replaced = False

        # determine the name of the primary key field and store it into the class variable
        # polymorphic_primary_key_name (it is needed by query.py)
        for f in new_class._meta.fields:
            if f.primary_key and type(f)!=models.OneToOneField:
                new_class.polymorphic_primary_key_name=f.name
                break

        return new_class

    def get_inherited_managers(self, attrs):
        """
        Return list of all managers to be inherited/propagated from the base classes;
        use correct mro, only use managers with _inherited==False (they are of no use),
        skip managers that are overwritten by the user with same-named class attributes (in attrs)
        """
        add_managers = []; add_managers_keys = set()
        for base in self.__mro__[1:]:
            if not issubclass(base, models.Model): continue
            if not getattr(base, 'polymorphic_model_marker', None): continue # leave managers of non-polym. models alone

            for key, manager in base.__dict__.items():
                if type(manager) == models.manager.ManagerDescriptor: manager = manager.manager
                if not isinstance(manager, models.Manager): continue
                if key in ['_base_manager']: continue       # let Django handle _base_manager
                if key in attrs: continue
                if key in add_managers_keys: continue       # manager with that name already added, skip
                if manager._inherited: continue             # inherited managers (on the bases) have no significance, they are just copies
                #print >>sys.stderr,'##',self.__name__, key
                if isinstance(manager, PolymorphicManager): # validate any inherited polymorphic managers
                    self.validate_model_manager(manager, self.__name__, key)
                add_managers.append((base.__name__, key, manager))
                add_managers_keys.add(key)
        return add_managers

    @classmethod
    def get_first_user_defined_manager(self, model_name, attrs):
        mgr_list = []
        for key, val in attrs.items():
            if not isinstance(val, models.Manager): continue
            mgr_list.append((val.creation_counter, key, val))
        # if there are user defined managers, use first one as _default_manager
        if mgr_list:                        #
            _, manager_name, manager = sorted(mgr_list)[0]
            #sys.stderr.write( '\n# first user defined manager for model "{model}":\n#  "{mgrname}": {mgr}\n#  manager model: {mgrmodel}\n\n'
            #    .format( model=model_name, mgrname=manager_name, mgr=manager, mgrmodel=manager.model ) )
            return manager
        return None

    @classmethod
    def call_superclass_new_method(self, model_name, bases, attrs):
        """call __new__ method of super class and return the newly created class.
        Also work around a limitation in Django's ModelBase."""
        # There seems to be a general limitation in Django's app_label handling
        # regarding abstract models (in ModelBase). See issue 1 on github - TODO: propose patch for Django
        # We run into this problem if polymorphic.py is located in a top-level directory
        # which is directly in the python path. To work around this we temporarily set
        # app_label here for PolymorphicModel.
        meta = attrs.get('Meta', None)
        model_module_name = attrs['__module__']
        do_app_label_workaround = (meta
                                    and model_module_name == 'polymorphic'
                                    and model_name == 'PolymorphicModel'
                                    and getattr(meta, 'app_label', None) is None )

        if do_app_label_workaround: meta.app_label = 'poly_dummy_app_label'
        new_class = super(PolymorphicModelBase, self).__new__(self, model_name, bases, attrs)
        if do_app_label_workaround: del(meta.app_label)
        return new_class

    def validate_model_fields(self):
        "check if all fields names are allowed (i.e. not in POLYMORPHIC_SPECIAL_Q_KWORDS)"
        for f in self._meta.fields:
            if f.name in POLYMORPHIC_SPECIAL_Q_KWORDS:
                e = 'PolymorphicModel: "%s" - field name "%s" is not allowed in polymorphic models'
                raise AssertionError(e % (self.__name__, f.name) )

    @classmethod
    def validate_model_manager(self, manager, model_name, manager_name):
        """check if the manager is derived from PolymorphicManager
        and its querysets from PolymorphicQuerySet - throw AssertionError if not"""

        if not issubclass(type(manager), PolymorphicManager):
            e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" manager is of type "' + type(manager).__name__
            e += '", but must be a subclass of PolymorphicManager'
            raise AssertionError(e)
        if not getattr(manager, 'queryset_class', None) or not issubclass(manager.queryset_class, PolymorphicQuerySet):
            e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" (PolymorphicManager) has been instantiated with a queryset class which is'
            e += ' not a subclass of PolymorphicQuerySet (which is required)'
            raise AssertionError(e)
        return manager


    # hack: a small patch to Django would be a better solution.
    # Django's management command 'dumpdata' relies on non-polymorphic
    # behaviour of the _default_manager. Therefore, we catch any access to _default_manager
    # here and return the non-polymorphic default manager instead if we are called from 'dumpdata.py'
    # (non-polymorphic default manager is 'base_objects' for polymorphic models).
    # This way we don't need to patch django.core.management.commands.dumpdata
    # for all supported Django versions.
    # TODO: investigate Django how this can be avoided
    _dumpdata_command_running = False
    if len(sys.argv)>1: _dumpdata_command_running = ( sys.argv[1] == 'dumpdata' )
    def __getattribute__(self, name):
        if name=='_default_manager':
            if self._dumpdata_command_running:
                frm = inspect.stack()[1] # frm[1] is caller file name, frm[3] is caller function name
                if 'django/core/management/commands/dumpdata.py' in frm[1]:
                    return self.base_objects
                #caller_mod_name = inspect.getmodule(frm[0]).__name__  # does not work with python 2.4
                #if caller_mod_name == 'django.core.management.commands.dumpdata':

        return super(PolymorphicModelBase, self).__getattribute__(name)