"""
Models for the forums application.
"""
import datetime

from django.db import models
from django.db.models import Q
from django.contrib.auth.models import User, Group
from django.core.cache import cache

from core.markup import site_markup
from oembed.models import Oembed


class Category(models.Model):
    """
    Forums belong to a category, whose access may be assigned to groups.
    """
    name = models.CharField(max_length=80)
    slug = models.SlugField(max_length=80)
    position = models.IntegerField(blank=True, default=0)
    groups = models.ManyToManyField(Group, blank=True, null=True,
        help_text="If groups are assigned to this category, only members" \
                    " of those groups can view this category.")

    class Meta:
        ordering = ('position', )
        verbose_name_plural = 'Categories'

    def __unicode__(self):
        return self.name


class ForumManager(models.Manager):
    """
    The manager for the Forum model. Provides a centralized place to
    put commonly used and useful queries.
    """

    def forums_for_user(self, user):
        """
        Returns a queryset containing the forums that the given user can
        "see" due to authenticated status, superuser status and group membership.
        """
        qs = self._for_user(user)
        return qs.select_related('category', 'last_post', 'last_post__user')

    def forum_ids_for_user(self, user):
        """Returns a list of forum IDs that the given user can "see"."""
        qs = self._for_user(user)
        return qs.values_list('id', flat=True)

    def public_forums(self):
        """Returns a queryset containing the public forums."""
        return self.filter(category__groups__isnull=True)

    def public_forum_ids(self):
        """
        Returns a list of ids for the public forums; the list is cached for
        performance.
        """
        public_forums = cache.get('public_forum_ids')
        if public_forums is None:
            public_forums = list(self.filter(
                category__groups__isnull=True).values_list('id', flat=True))
            cache.set('public_forum_ids', public_forums, 3600)
        return public_forums

    def _for_user(self, user):
        """Common code for the xxx_for_user() methods."""
        if user.is_superuser:
            qs = self.all()
        else:
            user_groups = user.groups.all() if user.is_authenticated() else []
            qs = self.filter(Q(category__groups__isnull=True) |
                    Q(category__groups__in=user_groups))
        return qs


class Forum(models.Model):
    """
    A forum is a collection of topics.
    """
    category = models.ForeignKey(Category, related_name='forums')
    name = models.CharField(max_length=80)
    slug = models.SlugField(max_length=80)
    description = models.TextField(blank=True, default='')
    position = models.IntegerField(blank=True, default=0)
    moderators = models.ManyToManyField(Group, blank=True, null=True)

    # denormalized fields to reduce database hits
    topic_count = models.IntegerField(blank=True, default=0)
    post_count = models.IntegerField(blank=True, default=0)
    last_post = models.OneToOneField('Post', blank=True, null=True,
        related_name='parent_forum')

    objects = ForumManager()

    class Meta:
        ordering = ('position', )

    def __unicode__(self):
        return self.name

    @models.permalink
    def get_absolute_url(self):
        return ('forums-forum_index', [self.slug])

    def topic_count_update(self):
        """Call to notify the forum that its topic count has been updated."""
        self.topic_count = Topic.objects.filter(forum=self).count()

    def post_count_update(self):
        """Call to notify the forum that its post count has been updated."""
        my_posts = Post.objects.filter(topic__forum=self)
        self.post_count = my_posts.count()
        if self.post_count > 0:
            self.last_post = my_posts[self.post_count - 1]
        else:
            self.last_post = None

    def sync(self):
        """
        Call to notify the forum that it needs to recompute its
        denormalized fields.
        """
        self.topic_count_update()
        self.post_count_update()

    def last_post_pre_delete(self, deleting_topic=False):
        """
        Call this function prior to deleting the last post in the forum.
        A new last post will be found, if one exists.
        This is to avoid the Django cascading delete issue.
        If deleting_topic is True, then the whole topic the last post is
        part of is being deleted, so we can't pick a new last post from that
        topic.
        """
        try:
            qs = Post.objects.filter(topic__forum=self)
            if deleting_topic:
                qs = qs.exclude(topic=self.last_post.topic)
            else:
                qs = qs.exclude(pk=self.last_post.pk)

            self.last_post = qs.latest()

        except Post.DoesNotExist:
            self.last_post = None

    def catchup(self, user, flv=None):
        """
        Call to mark this forum all caught up for the given user (i.e. mark all topics
        read for this user).
        """
        TopicLastVisit.objects.filter(user=user, topic__forum=self).delete()
        if flv is None:
            try:
                flv = ForumLastVisit.objects.get(user=user, forum=self)
            except ForumLastVisit.DoesNotExist:
                flv = ForumLastVisit(user=user, forum=self)

        now = datetime.datetime.now()
        flv.begin_date = now
        flv.end_date = now
        flv.save()


class Topic(models.Model):
    """
    A topic is a thread of discussion, consisting of a series of posts.
    """
    forum = models.ForeignKey(Forum, related_name='topics')
    name = models.CharField(max_length=255)
    creation_date = models.DateTimeField(db_index=True)
    user = models.ForeignKey(User)
    view_count = models.IntegerField(blank=True, default=0)
    sticky = models.BooleanField(blank=True, default=False)
    locked = models.BooleanField(blank=True, default=False)
    subscribers = models.ManyToManyField(User, related_name='subscriptions',
            verbose_name='subscribers', blank=True)
    bookmarkers = models.ManyToManyField(User, related_name='favorite_topics',
            verbose_name='bookmarkers', blank=True)

    # denormalized fields to reduce database hits
    post_count = models.IntegerField(blank=True, default=0)
    update_date = models.DateTimeField(db_index=True)
    last_post = models.OneToOneField('Post', blank=True, null=True,
        related_name='parent_topic')

    class Meta:
        ordering = ('-sticky', '-update_date', )

    def __unicode__(self):
        return self.name

    @models.permalink
    def get_absolute_url(self):
        return ('forums-topic_index', [self.pk])

    def post_count_update(self):
        """
        Call this function to notify the topic instance that its post count
        has changed.
        """
        my_posts = Post.objects.filter(topic=self)
        self.post_count = my_posts.count()
        if self.post_count > 0:
            self.last_post = my_posts[self.post_count - 1]
            self.update_date = self.last_post.creation_date
        else:
            self.last_post = None
            self.update_date = self.creation_date

    def reply_count(self):
        """
        Returns the number of replies to a topic. The first post
        doesn't count as a reply.
        """
        if self.post_count > 1:
            return self.post_count - 1
        return 0

    def save(self, *args, **kwargs):
        if not self.id:
            now = datetime.datetime.now()
            self.creation_date = now
            self.update_date = now

        super(Topic, self).save(*args, **kwargs)

    def last_post_pre_delete(self):
        """
        Call this function prior to deleting the last post in the topic.
        A new last post will be found, if one exists.
        This is to avoid the Django cascading delete issue.
        """
        try:
            self.last_post = \
                Post.objects.filter(topic=self).exclude(pk=self.last_post.pk).latest()
        except Post.DoesNotExist:
            self.last_post = None

    def search_title(self):
        if self.post_count == 1:
            post_text = "(1 post)"
        else:
            post_text = "(%d posts)" % self.post_count

        return u"%s by %s; %s" % (self.name, self.user.username, post_text)

    def search_summary(self):
        return u''


class Post(models.Model):
    """
    A post is an instance of a user's single contribution to a topic.
    """
    topic = models.ForeignKey(Topic, related_name='posts')
    user = models.ForeignKey(User, related_name='posts')
    creation_date = models.DateTimeField(db_index=True)
    update_date = models.DateTimeField(db_index=True)
    body = models.TextField()
    html = models.TextField()
    user_ip = models.IPAddressField(blank=True, default='', null=True)
    attachments = models.ManyToManyField(Oembed, through='Attachment')

    class Meta:
        ordering = ('creation_date', )
        get_latest_by = 'creation_date'
        verbose_name = 'forum post'
        verbose_name_plural = 'forum posts'

    @models.permalink
    def get_absolute_url(self):
        return ('forums-goto_post', [self.pk])

    def summary(self):
        LIMIT = 50
        if len(self.body) < LIMIT:
            return self.body
        return self.body[:LIMIT] + '...'

    def __unicode__(self):
        return self.summary()

    def save(self, *args, **kwargs):
        if not self.id:
            self.creation_date = datetime.datetime.now()
            self.update_date = self.creation_date

        self.html = site_markup(self.body)
        super(Post, self).save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        first_post_id = self.topic.posts.all()[0].id
        super(Post, self).delete(*args, **kwargs)
        if self.id == first_post_id:
            self.topic.delete()

    def has_been_edited(self):
        return self.update_date > self.creation_date

    def touch(self):
        """Call this function to indicate the post has been edited."""
        self.update_date = datetime.datetime.now()

    def search_title(self):
        return u"%s by %s" % (self.topic.name, self.user.username)

    def search_summary(self):
        return self.body


class FlaggedPost(models.Model):
    """This model represents a user flagging a post as inappropriate."""
    user = models.ForeignKey(User)
    post = models.ForeignKey(Post)
    flag_date = models.DateTimeField(auto_now_add=True)

    def __unicode__(self):
        return u'Post ID %s flagged by %s' % (self.post.id, self.user.username)

    class Meta:
        ordering = ('flag_date', )

    def get_post_url(self):
        return '<a href="%s">Post</a>' % self.post.get_absolute_url()
    get_post_url.allow_tags = True


class ForumLastVisit(models.Model):
    """
    This model records the last time a user visited a forum.
    It is used to compute if a user has unread topics in a forum.
    We keep track of a window of time, delimited by begin_date and end_date.
    Topics updated within this window are tracked, and may have TopicLastVisit
    objects.
    Marking a forum as all read sets the begin_date equal to the end_date.
    """
    user = models.ForeignKey(User)
    forum = models.ForeignKey(Forum)
    begin_date = models.DateTimeField()
    end_date = models.DateTimeField()

    class Meta:
        unique_together = ('user', 'forum')
        ordering = ('-end_date', )

    def __unicode__(self):
        return u'Forum: %d User: %d Date: %s' % (self.forum.id, self.user.id,
                self.end_date.strftime('%Y-%m-%d %H:%M:%S'))

    def is_caught_up(self):
        return self.begin_date == self.end_date


class TopicLastVisit(models.Model):
    """
    This model records the last time a user read a topic.
    Objects of this class exist for the window specified in the
    corresponding ForumLastVisit object.
    """
    user = models.ForeignKey(User)
    topic = models.ForeignKey(Topic)
    last_visit = models.DateTimeField(db_index=True)

    class Meta:
        unique_together = ('user', 'topic')
        ordering = ('-last_visit', )

    def __unicode__(self):
        return u'Topic: %d User: %d Date: %s' % (self.topic.id, self.user.id,
                self.last_visit.strftime('%Y-%m-%d %H:%M:%S'))

    def save(self, *args, **kwargs):
        if self.last_visit is None:
            self.touch()
        super(TopicLastVisit, self).save(*args, **kwargs)

    def touch(self):
        self.last_visit = datetime.datetime.now()


class Attachment(models.Model):
    """
    This model is a "through" table for the M2M relationship between forum
    posts and Oembed objects.
    """
    post = models.ForeignKey(Post)
    embed = models.ForeignKey(Oembed)
    order = models.IntegerField()

    class Meta:
        ordering = ('order', )

    def __unicode__(self):
        return u'Post %d, %s' % (self.post.pk, self.embed.title)