"""Tag service.

Manages tags applied to taggable entities.

Cf. ATOM specs  (+ for instance this discussion: http://edward.oconnor.cx/2007/02/representing-tags-in-atom)
Cf. ICOM 3.6.12 (Tag) et 3.6.13 (TagApplication.

Warning: the Activity Steams spec has a notion of tagging, but it's slightly
different than what we are used to in content management:
"Indicates that the actor has associated the object with the target.
For example, if the actor specifies that a particular user appears in a photo.
The object is the user and the target is the photo."

"""
from abilian.core.extensions import db
from abilian.core.entities import IdMixin

from sqlalchemy import Column, Integer, Unicode, ForeignKey, DateTime


class Tag(db.Model, IdMixin):
  """Persistent class representing a tag."""

  #: Unique, autogenerated id.
  id = Column(Integer, primary_key=True)

  #: The text associated to the tag
  term = Column(Unicode, nullable=False, unique=True)

  # Not sure we want the extra complexity, even though it's specified by Atom.
  #label = Column()

  # Also we might want: created_at, etc. Maybe a Tag should be an Entity?


class TagApplication(db.Model, IdMixin):
  """Persistent class representing a tag application on a taggable object.
  """

  #: Unique, autogenerated id.
  id = Column(Integer, primary_key=True)

  #: The actor that did the tagging.
  actor_id = Column(Integer, ForeignKey("user.id"))

  #: The entity (object) on which the tag has been applied.
  entity_id = Column(Integer)  # must point to a valid entity

  #: The time when the tag was applied.
  created_at = Column(DateTime, nullable=False)
