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."

  auto_delete = db.BooleanProperty(required=True, default=False)
  "If true, a tag instance should be deleted when tagged_count reaches zero."

  @classmethod
  def __key_name(cls, tag_name):
    return cls.__name__ + '_' + tag_name
    
  def remove_tagged(self, key):
    def remove_tagged_txn():
      if key in self.tagged:
        self.tagged.remove(key)
        self.tagged_count -= 1
        if not self.tagged_count and self.auto_delete:
          self.delete()
        else:
          self.put()
    db.run_in_transaction(remove_tagged_txn)
    self.__class__.expire_cached_tags()

  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)
    self.__class__.expire_cached_tags()
    
  def clear_tagged(self):
    def clear_tagged_txn():
      if self.auto_delete:
        self.delete()
      else:
        self.tagged = []
        self.tagged_count = 0
        self.put()
    db.run_in_transaction(clear_tagged_txn)
    self.__class__.expire_cached_tags()
        
  @classmethod
  def get_by_name(cls, tag_name):
    return cls.get_by_key_name(cls.__key_name(tag_name))
    
  @classmethod
  def get_tags_for_key(cls, key):
    "Set the tags for the datastore object represented by key."
    tags = db.Query(cls).filter('tagged =', key).fetch(1000)
    return tags
    
  @classmethod
  def get_or_create(cls, tag_name):
    "Get the Tag object that has the tag value given by tag_value."
    tag_key_name = cls.__key_name(tag_name)
    existing_tag = cls.get_by_key_name(tag_key_name)
    if existing_tag is None:
      # The tag does not yet exist, so create it.
      def create_tag_txn():
        new_tag = cls(key_name=tag_key_name, tag=tag_name)
        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."""
    tag_list = db.Query(cls).filter('tagged_count >', 0).order(
        "-tagged_count").fetch(limit)
            
    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

    cache_name = cls.__name__ + '_tags_by_name'
    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"

      tags = db.Query(cls).order(order_by).fetch(limit)
      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

    tags = memcache.get(cls.__name__ + '_popular_tags')
    if tags is None:
      tags = cls.get_tags_by_frequency(limit)
      memcache.add(cls.__name__ + '_popular_tags', tags, 3600)

    return tags

  @classmethod
  def expire_cached_tags(cls):
    from google.appengine.api import memcache

    memcache.delete(cls.__name__ + '_popular_tags')
    memcache.delete(cls.__name__ + '_tags_by_name_asc')
    memcache.delete(cls.__name__ + '_tags_by_name_desc')

  def __str__(self):
    """Returns the string representation of the entity's tag name.
    """

    return self.tag

def tag_property(tag_name):
  """Decorator that creates and returns a tag property to be used 
  in Google AppEngine model.

  Args:
    tag_name: name of the tag to be created.
  """

  def get_tags(self):
    """"Get a list of Tag objects for all Tags that apply to the
    specified entity.
    """

    if self._tags[tag_name] is None or len(self._tags[tag_name]) == 0:
      self._tags[tag_name] = self._tag_model[
          tag_name].get_tags_for_key(self.key())
    return self._tags[tag_name]

  def set_tags(self, seed):
    """Set a list of Tag objects for all Tags that apply to 
    the specified entity.
    """

    import types
    if type(seed['tags']) is types.UnicodeType:
      # Convert unicode to a plain string
      seed['tags'] = str(seed['tags'])
    if type(seed['tags']) is types.StringType:
      # Tags is a string, split it on tag_seperator into a list
      seed['tags'] = string.split(seed['tags'], self.tag_separator)
    if type(seed['tags']) is types.ListType:
      get_tags(self)
      # 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[tag_name][:]:
        if each_tag not in seed['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[tag_name].remove(each_tag)
      # Secondly, we will check to see if any tags have been added.
      for each_tag in seed['tags']:
        each_tag = string.strip(each_tag)
        if len(each_tag) > 0 and each_tag not in self._tags[tag_name]:
          # 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 = self._tag_model[tag_name].get_or_create(
              seed['scope'], each_tag)
          tag.add_tagged(self.key())
          self._tags[tag_name].append(tag)
    else:
      raise Exception, "tags must be either a unicode, a string or a list"

  return property(get_tags, set_tags)


class Taggable(object):
  """A mixin class that is used for making GAE Model classes taggable.

  This is an extended version of Taggable-mixin which allows for 
  multiple tag properties in the same AppEngine Model class.
  """
    
  def __init__(self, **kwargs):
    """The constructor class for Taggable, that creates a dictionary of tags.

    The difference from the original taggable in terms of interface is
    that, tag class is not used as the default tag model, since we don't
    have a default tag property created in this class now.

    Args:
      kwargs: keywords containing the name of the tags and arguments
          containing tag model to be used.
    """

    self._tags = {}
    self._tag_model = {}

    for tag_name in kwargs:
      self._tags[tag_name] = None
      self._tag_model[tag_name] = kwargs[tag_name]

    self.tag_separator = ", "

  def tags_string(self, tag_name, ret_list=False):
    """Create a formatted string version of this entity's tags.
    
    Args:
      tag_name: the name of the tag which must be formatted
      ret_list: if False sends a string, otherwise sends a Python list
    """

    tag_list = [each_tag.tag for each_tag in tag_name]

    if ret_list:
      return tag_list
    else:
      return self.tag_separator.join(tag_list)
