from __future__ import unicode_literals

import itertools
import logging

from django.apps import apps
from django.core.exceptions import PermissionDenied
from django.utils.encoding import force_text, python_2_unicode_compatible
from django.utils.translation import ugettext_lazy as _

from .exceptions import InvalidNamespace

logger = logging.getLogger(__name__)


@python_2_unicode_compatible
class PermissionNamespace(object):
    _registry = {}

    @classmethod
    def all(cls):
        return cls._registry.values()

    @classmethod
    def get(cls, name):
        try:
            return cls._registry[name]
        except KeyError:
            raise InvalidNamespace(
                'Invalid namespace name. This is probably an obsolete '
                'permission namespace, execute the management command '
                '"purgepermissions" and try again.'
            )

    def __init__(self, name, label):
        self.name = name
        self.label = label
        self.permissions = []
        self.__class__._registry[name] = self

    def __str__(self):
        return force_text(self.label)

    def add_permission(self, name, label):
        permission = Permission(namespace=self, name=name, label=label)
        self.permissions.append(permission)
        return permission


@python_2_unicode_compatible
class Permission(object):
    _permissions = {}
    _stored_permissions_cache = {}

    @classmethod
    def all(cls, as_choices=False):
        if as_choices:
            results = []

            for namespace, permissions in itertools.groupby(cls.all(), lambda entry: entry.namespace):
                permission_options = [
                    (force_text(permission.uuid), permission) for permission in permissions
                ]
                results.append(
                    (namespace, permission_options)
                )

            return results
        else:
            # Return sorted permisions by namespace.name
            return sorted(
                cls._permissions.values(), key=lambda x: x.namespace.name
            )

    @classmethod
    def check_permissions(cls, requester, permissions):
        try:
            for permission in permissions:
                if permission.stored_permission.requester_has_this(requester):
                    return True
        except TypeError:
            # Not a list of permissions, just one
            if permissions.stored_permission.requester_has_this(requester):
                return True

        logger.debug('User "%s" does not have permissions "%s"',
                     requester,
                     permissions)
        raise PermissionDenied(_('Insufficient permissions.'))

    @classmethod
    def get(cls, pk, proxy_only=False):
        if proxy_only:
            return cls._permissions[pk]
        else:
            return cls._permissions[pk].stored_permission

    @classmethod
    def get_for_holder(cls, holder):
        StoredPermission = apps.get_model(
            app_label='permissions', model_name='StoredPermission'
        )

        return StoredPermission.get_for_holder(holder)

    @classmethod
    def invalidate_cache(cls):
        cls._stored_permissions_cache = {}

    @classmethod
    def refresh(cls):
        for permission in cls.all():
            permission.stored_permission

    def __init__(self, namespace, name, label):
        self.namespace = namespace
        self.name = name
        self.label = label
        self.pk = self.uuid
        self.__class__._permissions[self.uuid] = self

    def __repr__(self):
        return self.pk

    def __str__(self):
        return force_text(self.label)

    @property
    def stored_permission(self):
        StoredPermission = apps.get_model(
            app_label='permissions', model_name='StoredPermission'
        )

        try:
            return self.__class__._stored_permissions_cache[self.uuid]
        except KeyError:
            stored_permission, created = StoredPermission.objects.get_or_create(
                namespace=self.namespace.name,
                name=self.name,
            )
            stored_permission.volatile_permission = self
            self.__class__._stored_permissions_cache[
                self.uuid
            ] = stored_permission
            return stored_permission

    @property
    def uuid(self):
        return '%s.%s' % (self.namespace.name, self.name)