import logging
from django.db.models import Count, Sum
from django.utils import timezone
from django.core.cache import cache
from django.db import models
from boards import settings

__author__ = 'neko259'


logger = logging.getLogger(__name__)


CACHE_KEY_OPENING_POST = 'opening_post_id'


class ThreadManager(models.Manager):
    def process_oldest_threads(self):
        """
         Preserves maximum thread count. If there are too many threads,
         archive or delete the old ones.
         """

        threads = Thread.objects.filter(archived=False).order_by('-bump_time')
        thread_count = threads.count()

        if thread_count > settings.MAX_THREAD_COUNT:
            num_threads_to_delete = thread_count - settings.MAX_THREAD_COUNT
            old_threads = threads[thread_count - num_threads_to_delete:]

            for thread in old_threads:
                if settings.ARCHIVE_THREADS:
                    self._archive_thread(thread)
                else:
                    thread.delete()

            logger.info('Processed %d old threads' % num_threads_to_delete)

    def _archive_thread(self, thread):
        thread.archived = True
        thread.bumpable = False
        thread.last_edit_time = timezone.now()
        thread.save(update_fields=['archived', 'last_edit_time', 'bumpable'])


class Thread(models.Model):
    objects = ThreadManager()

    class Meta:
        app_label = 'boards'

    tags = models.ManyToManyField('Tag')
    bump_time = models.DateTimeField()
    last_edit_time = models.DateTimeField()
    replies = models.ManyToManyField('Post', symmetrical=False, null=True,
                                     blank=True, related_name='tre+')
    archived = models.BooleanField(default=False)
    bumpable = models.BooleanField(default=True)

    def get_tags(self):
        """
        Gets a sorted tag list.
        """

        return self.tags.order_by('name')

    def bump(self):
        """
        Bumps (moves to up) thread if possible.
        """

        if self.can_bump():
            self.bump_time = timezone.now()

            if self.get_reply_count() >= settings.MAX_POSTS_PER_THREAD:
                self.bumpable = False

            logger.info('Bumped thread %d' % self.id)

    def get_reply_count(self):
        return self.replies.count()

    def get_images_count(self):
        return self.replies.annotate(images_count=Count(
                'images')).aggregate(Sum('images_count'))['images_count__sum']

    def can_bump(self):
        """
        Checks if the thread can be bumped by replying to it.
        """

        return self.bumpable

    def get_last_replies(self):
        """
        Gets several last replies, not including opening post
        """

        if settings.LAST_REPLIES_COUNT > 0:
            reply_count = self.get_reply_count()

            if reply_count > 0:
                reply_count_to_show = min(settings.LAST_REPLIES_COUNT,
                                          reply_count - 1)
                replies = self.get_replies()
                last_replies = replies[reply_count - reply_count_to_show:]

                return last_replies

    def get_skipped_replies_count(self):
        """
        Gets number of posts between opening post and last replies.
        """
        reply_count = self.get_reply_count()
        last_replies_count = min(settings.LAST_REPLIES_COUNT,
                                 reply_count - 1)
        return reply_count - last_replies_count - 1

    def get_replies(self, view_fields_only=False):
        """
        Gets sorted thread posts
        """

        query = self.replies.order_by('pub_time').prefetch_related('images')
        if view_fields_only:
            query = query.defer('poster_user_agent')
        return query.all()

    def get_replies_with_images(self, view_fields_only=False):
        return self.get_replies(view_fields_only).annotate(images_count=Count(
            'images')).filter(images_count__gt=0)

    def add_tag(self, tag):
        """
        Connects thread to a tag and tag to a thread
        """

        self.tags.add(tag)

    def get_opening_post(self, only_id=False):
        """
        Gets the first post of the thread
        """

        query = self.replies.order_by('pub_time')
        if only_id:
            query = query.only('id')
        opening_post = query.first()

        return opening_post

    def get_opening_post_id(self):
        """
        Gets ID of the first thread post.
        """

        cache_key = CACHE_KEY_OPENING_POST + str(self.id)
        opening_post_id = cache.get(cache_key)
        if not opening_post_id:
            opening_post_id = self.get_opening_post(only_id=True).id
            cache.set(cache_key, opening_post_id)

        return opening_post_id

    def __unicode__(self):
        return str(self.id)

    def get_pub_time(self):
        """
        Gets opening post's pub time because thread does not have its own one.
        """

        return self.get_opening_post().pub_time

    def delete(self, using=None):
        if self.replies.exists():
            self.replies.all().delete()

        super(Thread, self).delete(using)

    def __str__(self):
        return 'T#{}/{}'.format(self.id, self.get_opening_post_id())