"""
Models and managers for generic tagging.
"""
# Python 2.3 compatibility
try:
    set
except NameError:
    from sets import Set as set

from django.contrib.contenttypes import generic
from django.contrib.contenttypes.models import ContentType
from django.db import connection, models
from django.db.models.query import QuerySet
from django.utils.translation import ugettext_lazy as _

from tagging import settings
from tagging.utils import calculate_cloud, get_tag_list, get_queryset_and_model, parse_tag_input
from tagging.utils import LOGARITHMIC

qn = connection.ops.quote_name

############
# Managers #
############

class TagManager(models.Manager):
    def update_tags(self, obj, tag_names):
        """
        Update tags associated with an object.
        """
        ctype = ContentType.objects.get_for_model(obj)
        current_tags = list(self.filter(items__content_type__pk=ctype.pk,
                                        items__object_id=obj.pk))
        updated_tag_names = parse_tag_input(tag_names)
        if settings.FORCE_LOWERCASE_TAGS:
            updated_tag_names = [t.lower() for t in updated_tag_names]

        # Remove tags which no longer apply
        tags_for_removal = [tag for tag in current_tags \
                            if tag.name not in updated_tag_names]
        if len(tags_for_removal):
            TaggedItem._default_manager.filter(content_type__pk=ctype.pk,
                                               object_id=obj.pk,
                                               tag__in=tags_for_removal).delete()
        # Add new tags
        current_tag_names = [tag.name for tag in current_tags]
        for tag_name in updated_tag_names:
            if tag_name not in current_tag_names:
                tag, created = self.get_or_create(name=tag_name)
                TaggedItem._default_manager.create(tag=tag, object=obj)

    def add_tag(self, obj, tag_name):
        """
        Associates the given object with a tag.
        """
        tag_names = parse_tag_input(tag_name)
        if not len(tag_names):
            raise AttributeError(_('No tags were given: "%s".') % tag_name)
        if len(tag_names) > 1:
            raise AttributeError(_('Multiple tags were given: "%s".') % tag_name)
        tag_name = tag_names[0]
        if settings.FORCE_LOWERCASE_TAGS:
            tag_name = tag_name.lower()
        tag, created = self.get_or_create(name=tag_name)
        ctype = ContentType.objects.get_for_model(obj)
        TaggedItem._default_manager.get_or_create(
            tag=tag, content_type=ctype, object_id=obj.pk)

    def get_for_object(self, obj):
        """
        Create a queryset matching all tags associated with the given
        object.
        """
        ctype = ContentType.objects.get_for_model(obj)
        return self.filter(items__content_type__pk=ctype.pk,
                           items__object_id=obj.pk)

    def _get_usage(self, model, counts=False, min_count=None, extra_joins=None, extra_criteria=None, params=None):
        """
        Perform the custom SQL query for ``usage_for_model`` and
        ``usage_for_queryset``.
        """
        if min_count is not None: counts = True

        model_table = qn(model._meta.db_table)
        model_pk = '%s.%s' % (model_table, qn(model._meta.pk.column))
        query = """
        SELECT DISTINCT %(tag)s.id, %(tag)s.name%(count_sql)s
        FROM
            %(tag)s
            INNER JOIN %(tagged_item)s
                ON %(tag)s.id = %(tagged_item)s.tag_id
            INNER JOIN %(model)s
                ON %(tagged_item)s.object_id = %(model_pk)s
            %%s
        WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
            %%s
        GROUP BY %(tag)s.id, %(tag)s.name
        %%s
        ORDER BY %(tag)s.name ASC""" % {
            'tag': qn(self.model._meta.db_table),
            'count_sql': counts and (', COUNT(%s)' % model_pk) or '',
            'tagged_item': qn(TaggedItem._meta.db_table),
            'model': model_table,
            'model_pk': model_pk,
            'content_type_id': ContentType.objects.get_for_model(model).pk,
        }

        min_count_sql = ''
        if min_count is not None:
            min_count_sql = 'HAVING COUNT(%s) >= %%s' % model_pk
            params.append(min_count)

        cursor = connection.cursor()
        cursor.execute(query % (extra_joins, extra_criteria, min_count_sql), params)
        tags = []
        for row in cursor.fetchall():
            t = self.model(*row[:2])
            if counts:
                t.count = row[2]
            tags.append(t)
        return tags

    def usage_for_model(self, model, counts=False, min_count=None, filters=None):
        """
        Obtain a list of tags associated with instances of the given
        Model class.

        If ``counts`` is True, a ``count`` attribute will be added to
        each tag, indicating how many times it has been used against
        the Model class in question.

        If ``min_count`` is given, only tags which have a ``count``
        greater than or equal to ``min_count`` will be returned.
        Passing a value for ``min_count`` implies ``counts=True``.

        To limit the tags (and counts, if specified) returned to those
        used by a subset of the Model's instances, pass a dictionary
        of field lookups to be applied to the given Model as the
        ``filters`` argument.
        """
        if filters is None: filters = {}

        queryset = model._default_manager.filter()
        for f in filters.items():
            queryset.query.add_filter(f)
        usage = self.usage_for_queryset(queryset, counts, min_count)

        return usage

    def usage_for_queryset(self, queryset, counts=False, min_count=None):
        """
        Obtain a list of tags associated with instances of a model
        contained in the given queryset.

        If ``counts`` is True, a ``count`` attribute will be added to
        each tag, indicating how many times it has been used against
        the Model class in question.

        If ``min_count`` is given, only tags which have a ``count``
        greater than or equal to ``min_count`` will be returned.
        Passing a value for ``min_count`` implies ``counts=True``.
        """

        extra_joins = ' '.join(queryset.query.get_from_clause()[0][1:])
        where, params = queryset.query.where.as_sql()
        if where:
            extra_criteria = 'AND %s' % where
        else:
            extra_criteria = ''
        return self._get_usage(queryset.model, counts, min_count, extra_joins, extra_criteria, params)

    def related_for_model(self, tags, model, counts=False, min_count=None):
        """
        Obtain a list of tags related to a given list of tags - that
        is, other tags used by items which have all the given tags.

        If ``counts`` is True, a ``count`` attribute will be added to
        each tag, indicating the number of items which have it in
        addition to the given list of tags.

        If ``min_count`` is given, only tags which have a ``count``
        greater than or equal to ``min_count`` will be returned.
        Passing a value for ``min_count`` implies ``counts=True``.
        """
        if min_count is not None: counts = True
        tags = get_tag_list(tags)
        tag_count = len(tags)
        tagged_item_table = qn(TaggedItem._meta.db_table)
        query = """
        SELECT %(tag)s.id, %(tag)s.name%(count_sql)s
        FROM %(tagged_item)s INNER JOIN %(tag)s ON %(tagged_item)s.tag_id = %(tag)s.id
        WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
          AND %(tagged_item)s.object_id IN
          (
              SELECT %(tagged_item)s.object_id
              FROM %(tagged_item)s, %(tag)s
              WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
                AND %(tag)s.id = %(tagged_item)s.tag_id
                AND %(tag)s.id IN (%(tag_id_placeholders)s)
              GROUP BY %(tagged_item)s.object_id
              HAVING COUNT(%(tagged_item)s.object_id) = %(tag_count)s
          )
          AND %(tag)s.id NOT IN (%(tag_id_placeholders)s)
        GROUP BY %(tag)s.id, %(tag)s.name
        %(min_count_sql)s
        ORDER BY %(tag)s.name ASC""" % {
            'tag': qn(self.model._meta.db_table),
            'count_sql': counts and ', COUNT(%s.object_id)' % tagged_item_table or '',
            'tagged_item': tagged_item_table,
            'content_type_id': ContentType.objects.get_for_model(model).pk,
            'tag_id_placeholders': ','.join(['%s'] * tag_count),
            'tag_count': tag_count,
            'min_count_sql': min_count is not None and ('HAVING COUNT(%s.object_id) >= %%s' % tagged_item_table) or '',
        }

        params = [tag.pk for tag in tags] * 2
        if min_count is not None:
            params.append(min_count)

        cursor = connection.cursor()
        cursor.execute(query, params)
        related = []
        for row in cursor.fetchall():
            tag = self.model(*row[:2])
            if counts is True:
                tag.count = row[2]
            related.append(tag)
        return related

    def cloud_for_model(self, model, steps=4, distribution=LOGARITHMIC,
                        filters=None, min_count=None):
        """
        Obtain a list of tags associated with instances of the given
        Model, giving each tag a ``count`` attribute indicating how
        many times it has been used and a ``font_size`` attribute for
        use in displaying a tag cloud.

        ``steps`` defines the range of font sizes - ``font_size`` will
        be an integer between 1 and ``steps`` (inclusive).

        ``distribution`` defines the type of font size distribution
        algorithm which will be used - logarithmic or linear. It must
        be either ``tagging.utils.LOGARITHMIC`` or
        ``tagging.utils.LINEAR``.

        To limit the tags displayed in the cloud to those associated
        with a subset of the Model's instances, pass a dictionary of
        field lookups to be applied to the given Model as the
        ``filters`` argument.

        To limit the tags displayed in the cloud to those with a
        ``count`` greater than or equal to ``min_count``, pass a value
        for the ``min_count`` argument.
        """
        tags = list(self.usage_for_model(model, counts=True, filters=filters,
                                         min_count=min_count))
        return calculate_cloud(tags, steps, distribution)

class TaggedItemManager(models.Manager):
    """
    FIXME There's currently no way to get the ``GROUP BY`` and ``HAVING``
          SQL clauses required by many of this manager's methods into
          Django's ORM.

          For now, we manually execute a query to retrieve the PKs of
          objects we're interested in, then use the ORM's ``__in``
          lookup to return a ``QuerySet``.

          Now that the queryset-refactor branch is in the trunk, this can be
          tidied up significantly.
    """
    def get_by_model(self, queryset_or_model, tags):
        """
        Create a ``QuerySet`` containing instances of the specified
        model associated with a given tag or list of tags.
        """
        tags = get_tag_list(tags)
        tag_count = len(tags)
        if tag_count == 0:
            # No existing tags were given
            queryset, model = get_queryset_and_model(queryset_or_model)
            return model._default_manager.none()
        elif tag_count == 1:
            # Optimisation for single tag - fall through to the simpler
            # query below.
            tag = tags[0]
        else:
            return self.get_intersection_by_model(queryset_or_model, tags)

        queryset, model = get_queryset_and_model(queryset_or_model)
        content_type = ContentType.objects.get_for_model(model)
        opts = self.model._meta
        tagged_item_table = qn(opts.db_table)
        return queryset.extra(
            tables=[opts.db_table],
            where=[
                '%s.content_type_id = %%s' % tagged_item_table,
                '%s.tag_id = %%s' % tagged_item_table,
                '%s.%s = %s.object_id' % (qn(model._meta.db_table),
                                          qn(model._meta.pk.column),
                                          tagged_item_table)
            ],
            params=[content_type.pk, tag.pk],
        )

    def get_intersection_by_model(self, queryset_or_model, tags):
        """
        Create a ``QuerySet`` containing instances of the specified
        model associated with *all* of the given list of tags.
        """
        tags = get_tag_list(tags)
        tag_count = len(tags)
        queryset, model = get_queryset_and_model(queryset_or_model)

        if not tag_count:
            return model._default_manager.none()

        model_table = qn(model._meta.db_table)
        # This query selects the ids of all objects which have all the
        # given tags.
        query = """
        SELECT %(model_pk)s
        FROM %(model)s, %(tagged_item)s
        WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
          AND %(tagged_item)s.tag_id IN (%(tag_id_placeholders)s)
          AND %(model_pk)s = %(tagged_item)s.object_id
        GROUP BY %(model_pk)s
        HAVING COUNT(%(model_pk)s) = %(tag_count)s""" % {
            'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
            'model': model_table,
            'tagged_item': qn(self.model._meta.db_table),
            'content_type_id': ContentType.objects.get_for_model(model).pk,
            'tag_id_placeholders': ','.join(['%s'] * tag_count),
            'tag_count': tag_count,
        }

        cursor = connection.cursor()
        cursor.execute(query, [tag.pk for tag in tags])
        object_ids = [row[0] for row in cursor.fetchall()]
        if len(object_ids) > 0:
            return queryset.filter(pk__in=object_ids)
        else:
            return model._default_manager.none()

    def get_union_by_model(self, queryset_or_model, tags):
        """
        Create a ``QuerySet`` containing instances of the specified
        model associated with *any* of the given list of tags.
        """
        tags = get_tag_list(tags)
        tag_count = len(tags)
        queryset, model = get_queryset_and_model(queryset_or_model)

        if not tag_count:
            return model._default_manager.none()

        model_table = qn(model._meta.db_table)
        # This query selects the ids of all objects which have any of
        # the given tags.
        query = """
        SELECT %(model_pk)s
        FROM %(model)s, %(tagged_item)s
        WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
          AND %(tagged_item)s.tag_id IN (%(tag_id_placeholders)s)
          AND %(model_pk)s = %(tagged_item)s.object_id
        GROUP BY %(model_pk)s""" % {
            'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
            'model': model_table,
            'tagged_item': qn(self.model._meta.db_table),
            'content_type_id': ContentType.objects.get_for_model(model).pk,
            'tag_id_placeholders': ','.join(['%s'] * tag_count),
        }

        cursor = connection.cursor()
        cursor.execute(query, [tag.pk for tag in tags])
        object_ids = [row[0] for row in cursor.fetchall()]
        if len(object_ids) > 0:
            return queryset.filter(pk__in=object_ids)
        else:
            return model._default_manager.none()

    def get_related(self, obj, queryset_or_model, num=None):
        """
        Retrieve a list of instances of the specified model which share
        tags with the model instance ``obj``, ordered by the number of
        shared tags in descending order.

        If ``num`` is given, a maximum of ``num`` instances will be
        returned.
        """
        queryset, model = get_queryset_and_model(queryset_or_model)
        model_table = qn(model._meta.db_table)
        content_type = ContentType.objects.get_for_model(obj)
        related_content_type = ContentType.objects.get_for_model(model)
        query = """
        SELECT %(model_pk)s, COUNT(related_tagged_item.object_id) AS %(count)s
        FROM %(model)s, %(tagged_item)s, %(tag)s, %(tagged_item)s related_tagged_item
        WHERE %(tagged_item)s.object_id = %%s
          AND %(tagged_item)s.content_type_id = %(content_type_id)s
          AND %(tag)s.id = %(tagged_item)s.tag_id
          AND related_tagged_item.content_type_id = %(related_content_type_id)s
          AND related_tagged_item.tag_id = %(tagged_item)s.tag_id
          AND %(model_pk)s = related_tagged_item.object_id"""
        if content_type.pk == related_content_type.pk:
            # Exclude the given instance itself if determining related
            # instances for the same model.
            query += """
          AND related_tagged_item.object_id != %(tagged_item)s.object_id"""
        query += """
        GROUP BY %(model_pk)s
        ORDER BY %(count)s DESC
        %(limit_offset)s"""
        query = query % {
            'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
            'count': qn('count'),
            'model': model_table,
            'tagged_item': qn(self.model._meta.db_table),
            'tag': qn(self.model._meta.get_field('tag').rel.to._meta.db_table),
            'content_type_id': content_type.pk,
            'related_content_type_id': related_content_type.pk,
            # Hardcoding this for now just to get tests working again - this
            # should now be handled by the query object.
            'limit_offset': num is not None and 'LIMIT %s' or '',
        }

        cursor = connection.cursor()
        params = [obj.pk]
        if num is not None:
            params.append(num)
        cursor.execute(query, params)
        object_ids = [row[0] for row in cursor.fetchall()]
        if len(object_ids) > 0:
            # Use in_bulk here instead of an id__in lookup, because id__in would
            # clobber the ordering.
            object_dict = queryset.in_bulk(object_ids)
            return [object_dict[object_id] for object_id in object_ids \
                    if object_id in object_dict]
        else:
            return []

##########
# Models #
##########

class Tag(models.Model):
    """
    A tag.
    """
    name = models.CharField(_('name'), max_length=50, unique=True, db_index=True)

    objects = TagManager()

    class Meta:
        ordering = ('name',)
        verbose_name = _('tag')
        verbose_name_plural = _('tags')

    def __unicode__(self):
        return self.name

class TaggedItem(models.Model):
    """
    Holds the relationship between a tag and the item being tagged.
    """
    tag          = models.ForeignKey(Tag, verbose_name=_('tag'), related_name='items')
    content_type = models.ForeignKey(ContentType, verbose_name=_('content type'))
    object_id    = models.PositiveIntegerField(_('object id'), db_index=True)
    object       = generic.GenericForeignKey('content_type', 'object_id')

    objects = TaggedItemManager()

    class Meta:
        # Enforce unique tag association per object
        unique_together = (('tag', 'content_type', 'object_id'),)
        verbose_name = _('tagged item')
        verbose_name_plural = _('tagged items')

    def __unicode__(self):
        return u'%s [%s]' % (self.object, self.tag)
