import itertools

from django.contrib.contenttypes.fields import GenericRelation
from django.core.cache import cache
from django.core.exceptions import ObjectDoesNotExist
from django.core.validators import RegexValidator
from django.db import models
from django.db.models import CASCADE
from django.urls import reverse
from django.utils.functional import cached_property
from django.utils.translation import gettext_lazy as _
from mptt.fields import TreeForeignKey
from mptt.models import MPTTModel
from reversion.models import Version

from judge.models.contest import Contest
from judge.models.interface import BlogPost
from judge.models.problem import Problem
from judge.models.profile import Profile
from judge.utils.cachedict import CacheDict


__all__ = ['Comment', 'CommentLock', 'CommentVote', 'Notification']

comment_validator = RegexValidator(r'^[pcs]:[a-z0-9]+$|^b:\d+$',
                                   _(r'Page code must be ^[pcs]:[a-z0-9]+$|^b:\d+$'))


class VersionRelation(GenericRelation):
    def __init__(self):
        super(VersionRelation, self).__init__(Version, object_id_field='object_id')

    def get_extra_restriction(self, where_class, alias, remote_alias):
        cond = super(VersionRelation, self).get_extra_restriction(where_class, alias, remote_alias)
        field = self.remote_field.model._meta.get_field('db')
        lookup = field.get_lookup('exact')(field.get_col(remote_alias), 'default')
        cond.add(lookup, 'AND')
        return cond


class Comment(MPTTModel):
    author = models.ForeignKey(Profile, verbose_name=_('commenter'), on_delete=CASCADE)
    time = models.DateTimeField(verbose_name=_('posted time'), auto_now_add=True)
    page = models.CharField(max_length=30, verbose_name=_('associated page'), db_index=True,
                            validators=[comment_validator])
    score = models.IntegerField(verbose_name=_('votes'), default=0)
    body = models.TextField(verbose_name=_('body of comment'), max_length=8192)
    hidden = models.BooleanField(verbose_name=_('hide the comment'), default=0)
    parent = TreeForeignKey('self', verbose_name=_('parent'), null=True, blank=True, related_name='replies',
                            on_delete=CASCADE)
    versions = VersionRelation()

    class Meta:
        verbose_name = _('comment')
        verbose_name_plural = _('comments')

    class MPTTMeta:
        order_insertion_by = ['-time']

    @classmethod
    def most_recent(cls, user, n, batch=None):
        queryset = cls.objects.filter(hidden=False).select_related('author__user') \
            .defer('author__about', 'body').order_by('-id')

        problem_access = CacheDict(lambda code: Problem.objects.get(code=code).is_accessible_by(user))
        contest_access = CacheDict(lambda key: Contest.objects.get(key=key).is_accessible_by(user))
        blog_access = CacheDict(lambda id: BlogPost.objects.get(id=id).can_see(user))

        if user.is_superuser:
            return queryset[:n]
        if batch is None:
            batch = 2 * n
        output = []
        for i in itertools.count(0):
            slice = queryset[i * batch:i * batch + batch]
            if not slice:
                break
            for comment in slice:
                if comment.page.startswith('p:') or comment.page.startswith('s:'):
                    try:
                        if problem_access[comment.page[2:]]:
                            output.append(comment)
                    except Problem.DoesNotExist:
                        pass
                elif comment.page.startswith('c:'):
                    try:
                        if contest_access[comment.page[2:]]:
                            output.append(comment)
                    except Contest.DoesNotExist:
                        pass
                elif comment.page.startswith('b:'):
                    try:
                        if blog_access[comment.page[2:]]:
                            output.append(comment)
                    except BlogPost.DoesNotExist:
                        pass
                else:
                    output.append(comment)
                if len(output) >= n:
                    return output
        return output

    @cached_property
    def link(self):
        try:
            link = None
            if self.page.startswith('p:'):
                link = reverse('problem_detail', args=(self.page[2:],))
            elif self.page.startswith('c:'):
                link = reverse('contest_view', args=(self.page[2:],))
            elif self.page.startswith('b:'):
                key = 'blog_slug:%s' % self.page[2:]
                slug = cache.get(key)
                if slug is None:
                    try:
                        slug = BlogPost.objects.get(id=self.page[2:]).slug
                    except ObjectDoesNotExist:
                        slug = ''
                    cache.set(key, slug, 3600)
                link = reverse('blog_post', args=(self.page[2:], slug))
            elif self.page.startswith('s:'):
                link = reverse('problem_editorial', args=(self.page[2:],))
        except Exception:
            link = 'invalid'
        return link

    @classmethod
    def get_page_title(cls, page):
        try:
            if page.startswith('p:'):
                return Problem.objects.values_list('name', flat=True).get(code=page[2:])
            elif page.startswith('c:'):
                return Contest.objects.values_list('name', flat=True).get(key=page[2:])
            elif page.startswith('b:'):
                return BlogPost.objects.values_list('title', flat=True).get(id=page[2:])
            elif page.startswith('s:'):
                return _('Editorial for %s') % Problem.objects.values_list('name', flat=True).get(code=page[2:])
            return '<unknown>'
        except ObjectDoesNotExist:
            return '<deleted>'

    @cached_property
    def page_title(self):
        return self.get_page_title(self.page)

    def get_absolute_url(self):
        return '%s#comment-%d' % (self.link, self.id)

    def __str__(self):
        return '%(page)s by %(user)s' % {'page': self.page, 'user': self.author.user.username}

        # Only use this when queried with
        # .prefetch_related(Prefetch('votes', queryset=CommentVote.objects.filter(voter_id=profile_id)))
        # It's rather stupid to put a query specific property on the model, but the alternative requires
        # digging Django internals, and could not be guaranteed to work forever.
        # Hence it is left here for when the alternative breaks.
        # @property
        # def vote_score(self):
        #    queryset = self.votes.all()
        #    if not queryset:
        #        return 0
        #    return queryset[0].score


class CommentVote(models.Model):
    voter = models.ForeignKey(Profile, related_name='voted_comments', on_delete=CASCADE)
    comment = models.ForeignKey(Comment, related_name='votes', on_delete=CASCADE)
    score = models.IntegerField()

    class Meta:
        unique_together = ['voter', 'comment']
        verbose_name = _('comment vote')
        verbose_name_plural = _('comment votes')


class CommentLock(models.Model):
    page = models.CharField(max_length=30, verbose_name=_('associated page'), db_index=True,
                            validators=[comment_validator])

    class Meta:
        permissions = (
            ('override_comment_lock', _('Override comment lock')),
        )

    def __str__(self):
        return str(self.page)


class Notification(models.Model):
    owner = models.ForeignKey(Profile, verbose_name=_('owner'), related_name="notifications", on_delete=CASCADE)
    time = models.DateTimeField(verbose_name=_('posted time'), auto_now_add=True)
    comment = models.ForeignKey(Comment, verbose_name=_('comment'), on_delete=CASCADE)
    read = models.BooleanField(verbose_name=_('read'), default=False)
    category = models.CharField(verbose_name=_('category'), max_length=10)