from datetime import datetime

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.utils.translation import ugettext_lazy as _
from django.db.models.fields import FieldDoesNotExist
from django.core.exceptions import ImproperlyConfigured

from model_utils.managers import manager_from, InheritanceCastMixin, \
    QueryManager
from model_utils.fields import AutoCreatedField, AutoLastModifiedField, \
    StatusField, MonitorField

class InheritanceCastModel(models.Model):
    """
    An abstract base class that provides a ``real_type`` FK to ContentType.

    For use in trees of inherited models, to be able to downcast
    parent instances to their child types.

    """
    real_type = models.ForeignKey(ContentType, editable=False, null=True)

    objects = manager_from(InheritanceCastMixin)

    def save(self, *args, **kwargs):
        if not self.id:
            self.real_type = self._get_real_type()
        super(InheritanceCastModel, self).save(*args, **kwargs)

    def _get_real_type(self):
        return ContentType.objects.get_for_model(type(self))

    def cast(self):
        return self.real_type.get_object_for_this_type(pk=self.pk)

    class Meta:
        abstract = True


class TimeStampedModel(models.Model):
    """
    An abstract base class model that provides self-updating
    ``created`` and ``modified`` fields.

    """
    created = AutoCreatedField(_('created'))
    modified = AutoLastModifiedField(_('modified'))

    class Meta:
        abstract = True


class TimeFramedModel(models.Model):
    """
    An abstract base class model that provides ``start``
    and ``end`` fields to record a timeframe.

    """
    start = models.DateTimeField(_('start'), null=True, blank=True)
    end = models.DateTimeField(_('end'), null=True, blank=True)

    class Meta:
        abstract = True

class StatusModel(models.Model):
    """
    An abstract base class model with a ``status`` field that
    automatically uses a ``STATUS`` class attribute of choices, a
    ``status_changed`` date-time field that records when ``status``
    was last modified, and an automatically-added manager for each
    status that returns objects with that status only.

    """
    status = StatusField(_('status'))
    status_changed = MonitorField(_('status changed'), monitor='status')

    class Meta:
        abstract = True

def add_status_query_managers(sender, **kwargs):
    """
    Add a Querymanager for each status item dynamically.

    """
    if not issubclass(sender, StatusModel):
        return
    for value, name in getattr(sender, 'STATUS', ()):
        try:
            sender._meta.get_field(name)
            raise ImproperlyConfigured("StatusModel: Model '%s' has a field "
                                       "named '%s' which conflicts with a "
                                       "status of the same name."
                                       % (sender.__name__, name))
        except FieldDoesNotExist:
            pass
        sender.add_to_class(value, QueryManager(status=value))

def add_timeframed_query_manager(sender, **kwargs):
    """
    Add a QueryManager for a specific timeframe.

    """
    if not issubclass(sender, TimeFramedModel):
        return
    try:
        sender._meta.get_field('timeframed')
        raise ImproperlyConfigured("Model '%s' has a field named "
                                   "'timeframed' which conflicts with "
                                   "the TimeFramedModel manager." 
                                   % sender.__name__)
    except FieldDoesNotExist:
        pass
    sender.add_to_class('timeframed', QueryManager(
        (models.Q(start__lte=datetime.now) | models.Q(start__isnull=True)) &
        (models.Q(end__gte=datetime.now) | models.Q(end__isnull=True))
    ))


models.signals.class_prepared.connect(add_status_query_managers)
models.signals.class_prepared.connect(add_timeframed_query_manager)