from google.appengine.ext import db

import string

class Tag(db.Model):

    "Google AppEngine model for store of tags."

    tag = db.StringProperty(required=True)

    "The actual string value of the tag."

    added = db.DateTimeProperty(auto_now_add=True)

    "The date and time that the tag was first added to the datastore."

    tagged = db.ListProperty(db.Key)

    "A List of db.Key values for the datastore objects that have been tagged with this tag value."

    tagged_count = db.IntegerProperty(default=0)

    "The number of entities in tagged."

    def remove_tagged(self, key):

        def remove_tagged_txn():

            if key in self.tagged:

                self.tagged.remove(key)

                self.tagged_count -= 1

                self.put()

        db.run_in_transaction(remove_tagged_txn)

    def add_tagged(self, key):

        def add_tagged_txn():

            if key not in self.tagged:

                self.tagged.append(key)

                self.tagged_count += 1

                self.put()

        db.run_in_transaction(add_tagged_txn)

    def clear_tagged(self):

        def clear_tagged_txn():

            self.tagged = []

            self.tagged_count = 0

            self.put()

        db.run_in_transaction(clear_tagged_txn)

    @classmethod

    def get_by_name(cls, tag_name):

    @classmethod

    def get_tags_for_key(cls, key):

        "Set the tags for the datastore object represented by key."

        return tags

    @classmethod

    def get_or_create(cls, tag_name):

        "Get the Tag object that has the tag value given by tag_value."

        if existing_tag is None:

            # The tag does not yet exist, so create it.

            def create_tag_txn():

                new_tag.put()

                return new_tag

            existing_tag = db.run_in_transaction(create_tag_txn)

        return existing_tag

    @classmethod

    def get_tags_by_frequency(cls, limit=1000):

        """Return a list of Tags sorted by the number of objects to which they have been applied,

        most frequently-used first.  If limit is given, return only that many tags; otherwise,

        return all."""

        return tag_list

    @classmethod

    def get_tags_by_name(cls, limit=1000, ascending=True):

        """Return a list of Tags sorted alphabetically by the name of the tag.

        If a limit is given, return only that many tags; otherwise, return all.

        If ascending is True, sort from a-z; otherwise, sort from z-a."""

        from google.appengine.api import memcache

        if ascending:

            cache_name += '_asc'

        else:

            cache_name += '_desc'

        tags = memcache.get(cache_name)

        if tags is None or len(tags) < limit:

            order_by = "tag"

            if not ascending:

                order_by = "-tag"

            memcache.add(cache_name, tags, 3600)

        else:

            if len(tags) > limit:

                # Return only as many as requested.

                tags = tags[:limit]

        return tags

    @classmethod

    def popular_tags(cls, limit=5):

        from google.appengine.api import memcache

        if tags is None:

        return tags

    @classmethod

    def expire_cached_tags(cls):

        from google.appengine.api import memcache

class Taggable:

        Usage:

            class Post(db.Model, taggable.Taggable):

                body = db.TextProperty(required = True)

                title = db.StringProperty()

                added = db.DateTimeProperty(auto_now_add=True)

                edited = db.DateTimeProperty()

                def __init__(self, parent=None, key_name=None, app=None, **entity_values):

                    db.Model.__init__(self, parent, key_name, app, **entity_values)

                    taggable.Taggable.__init__(self)

    """

        self.__tags = None

        self.tag_separator = ","

        """The string that is used to separate individual tags in a string

        representation of a list of tags.  Used by tags_string() to join the tags

        into a string representation and tags setter to split a string into

        individual tags."""

    def __get_tags(self):

        "Get a List of Tag objects for all Tags that apply to this object."

        if self.__tags is None or len(self.__tags) == 0:

        return self.__tags

    def __set_tags(self, tags):

        import types

        if type(tags) is types.UnicodeType:

            # Convert unicode to a plain string

            tags = str(tags)

        if type(tags) is types.StringType:

            # Tags is a string, split it on tag_seperator into a list

            tags = string.split(tags, self.tag_separator)

        if type(tags) is types.ListType:

            self.__get_tags()

            # Firstly, we will check to see if any tags have been removed.

            # Iterate over a copy of __tags, as we may need to modify __tags

            for each_tag in self.__tags[:]:

                if each_tag not in tags:

                    # A tag that was previously assigned to this entity is

                    # missing in the list that is being assigned, so we

                    # disassocaite this entity and the tag.

                    each_tag.remove_tagged(self.key())

                    self.__tags.remove(each_tag)

            # Secondly, we will check to see if any tags have been added.

            for each_tag in tags:

                each_tag = string.strip(each_tag)

                if len(each_tag) > 0 and each_tag not in self.__tags:

                    # A tag that was not previously assigned to this entity

                    # is present in the list that is being assigned, so we

                    # associate this entity with the tag.

                    tag.add_tagged(self.key())

                    self.__tags.append(tag)

        else:

            raise Exception, "tags must be either a unicode, a string or a list"

    tags = property(__get_tags, __set_tags, None, None)

    def tags_string(self):

        "Create a formatted string version of this entity's tags"

        to_str = ""

        for each_tag in self.tags:

            to_str += each_tag.tag

            if each_tag != self.tags[-1]:

                to_str += self.tag_separator

        return to_str