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+"""
+A generic comment-moderation system which allows configuration of
+moderation options on a per-model basis.
+
+To use, do two things:
+
+1. Create or import a subclass of ``CommentModerator`` defining the
+   options you want.
+
+2. Import ``moderator`` from this module and register one or more
+   models, passing the models and the ``CommentModerator`` options
+   class you want to use.
+
+
+Example
+-------
+
+First, we define a simple model class which might represent entries in
+a Weblog::
+
+    from django.db import models
+
+    class Entry(models.Model):
+        title = models.CharField(max_length=250)
+        body = models.TextField()
+        pub_date = models.DateField()
+        enable_comments = models.BooleanField()
+
+Then we create a ``CommentModerator`` subclass specifying some
+moderation options::
+
+    from django_comments.moderation import CommentModerator, moderator
+
+    class EntryModerator(CommentModerator):
+        email_notification = True
+        enable_field = 'enable_comments'
+
+And finally register it for moderation::
+
+    moderator.register(Entry, EntryModerator)
+
+This sample class would apply two moderation steps to each new
+comment submitted on an Entry:
+
+* If the entry's ``enable_comments`` field is set to ``False``, the
+  comment will be rejected (immediately deleted).
+
+* If the comment is successfully posted, an email notification of the
+  comment will be sent to site staff.
+
+For a full list of built-in moderation options and other
+configurability, see the documentation for the ``CommentModerator``
+class.
+
+"""
+
+import datetime
+
+from django.conf import settings
+from django.contrib.sites.shortcuts import get_current_site
+from django.core.mail import send_mail
+from django.db.models.base import ModelBase
+from django.template import loader
+from django.utils import timezone
+from django.utils.translation import ugettext as _
+
+import django_comments
+from django_comments import signals
+
+
+class AlreadyModerated(Exception):
+    """
+    Raised when a model which is already registered for moderation is
+    attempting to be registered again.
+
+    """
+    pass
+
+
+class NotModerated(Exception):
+    """
+    Raised when a model which is not registered for moderation is
+    attempting to be unregistered.
+
+    """
+    pass
+
+
+class CommentModerator(object):
+    """
+    Encapsulates comment-moderation options for a given model.
+
+    This class is not designed to be used directly, since it doesn't
+    enable any of the available moderation options. Instead, subclass
+    it and override attributes to enable different options::
+
+    ``auto_close_field``
+        If this is set to the name of a ``DateField`` or
+        ``DateTimeField`` on the model for which comments are
+        being moderated, new comments for objects of that model
+        will be disallowed (immediately deleted) when a certain
+        number of days have passed after the date specified in
+        that field. Must be used in conjunction with
+        ``close_after``, which specifies the number of days past
+        which comments should be disallowed. Default value is
+        ``None``.
+
+    ``auto_moderate_field``
+        Like ``auto_close_field``, but instead of outright
+        deleting new comments when the requisite number of days
+        have elapsed, it will simply set the ``is_public`` field
+        of new comments to ``False`` before saving them. Must be
+        used in conjunction with ``moderate_after``, which
+        specifies the number of days past which comments should be
+        moderated. Default value is ``None``.
+
+    ``close_after``
+        If ``auto_close_field`` is used, this must specify the
+        number of days past the value of the field specified by
+        ``auto_close_field`` after which new comments for an
+        object should be disallowed. Default value is ``None``.
+
+    ``email_notification``
+        If ``True``, any new comment on an object of this model
+        which survives moderation will generate an email to site
+        staff. Default value is ``False``.
+
+    ``enable_field``
+        If this is set to the name of a ``BooleanField`` on the
+        model for which comments are being moderated, new comments
+        on objects of that model will be disallowed (immediately
+        deleted) whenever the value of that field is ``False`` on
+        the object the comment would be attached to. Default value
+        is ``None``.
+
+    ``moderate_after``
+        If ``auto_moderate_field`` is used, this must specify the number
+        of days past the value of the field specified by
+        ``auto_moderate_field`` after which new comments for an
+        object should be marked non-public. Default value is
+        ``None``.
+
+    Most common moderation needs can be covered by changing these
+    attributes, but further customization can be obtained by
+    subclassing and overriding the following methods. Each method will
+    be called with three arguments: ``comment``, which is the comment
+    being submitted, ``content_object``, which is the object the
+    comment will be attached to, and ``request``, which is the
+    ``HttpRequest`` in which the comment is being submitted::
+
+    ``allow``
+        Should return ``True`` if the comment should be allowed to
+        post on the content object, and ``False`` otherwise (in
+        which case the comment will be immediately deleted).
+
+    ``email``
+        If email notification of the new comment should be sent to
+        site staff or moderators, this method is responsible for
+        sending the email.
+
+    ``moderate``
+        Should return ``True`` if the comment should be moderated
+        (in which case its ``is_public`` field will be set to
+        ``False`` before saving), and ``False`` otherwise (in
+        which case the ``is_public`` field will not be changed).
+
+    Subclasses which want to introspect the model for which comments
+    are being moderated can do so through the attribute ``_model``,
+    which will be the model class.
+
+    """
+    auto_close_field = None
+    auto_moderate_field = None
+    close_after = None
+    email_notification = False
+    enable_field = None
+    moderate_after = None
+
+    def __init__(self, model):
+        self._model = model
+
+    def _get_delta(self, now, then):
+        """
+        Internal helper which will return a ``datetime.timedelta``
+        representing the time between ``now`` and ``then``. Assumes
+        ``now`` is a ``datetime.date`` or ``datetime.datetime`` later
+        than ``then``.
+
+        If ``now`` and ``then`` are not of the same type due to one of
+        them being a ``datetime.date`` and the other being a
+        ``datetime.datetime``, both will be coerced to
+        ``datetime.date`` before calculating the delta.
+
+        """
+        if now.__class__ is not then.__class__:
+            now = datetime.date(now.year, now.month, now.day)
+            then = datetime.date(then.year, then.month, then.day)
+        if now < then:
+            raise ValueError("Cannot determine moderation rules because date field is set to a value in the future")
+        return now - then
+
+    def allow(self, comment, content_object, request):
+        """
+        Determine whether a given comment is allowed to be posted on
+        a given object.
+
+        Return ``True`` if the comment should be allowed, ``False
+        otherwise.
+
+        """
+        if self.enable_field:
+            if not getattr(content_object, self.enable_field):
+                return False
+        if self.auto_close_field and self.close_after is not None:
+            close_after_date = getattr(content_object, self.auto_close_field)
+            if close_after_date is not None and self._get_delta(timezone.now(),
+                                                                close_after_date).days >= self.close_after:
+                return False
+        return True
+
+    def moderate(self, comment, content_object, request):
+        """
+        Determine whether a given comment on a given object should be
+        allowed to show up immediately, or should be marked non-public
+        and await approval.
+
+        Return ``True`` if the comment should be moderated (marked
+        non-public), ``False`` otherwise.
+
+        """
+        if self.auto_moderate_field and self.moderate_after is not None:
+            moderate_after_date = getattr(content_object, self.auto_moderate_field)
+            if moderate_after_date is not None and self._get_delta(timezone.now(),
+                                                                   moderate_after_date).days >= self.moderate_after:
+                return True
+        return False
+
+    def email(self, comment, content_object, request):
+        """
+        Send email notification of a new comment to site staff when email
+        notifications have been requested.
+
+        """
+        if not self.email_notification:
+            return
+        recipient_list = [manager_tuple[1] for manager_tuple in settings.MANAGERS]
+        t = loader.get_template('comments/comment_notification_email.txt')
+        c = {
+            'comment': comment,
+            'content_object': content_object,
+        }
+        subject = _('[%(site)s] New comment posted on "%(object)s"') % {
+            'site': get_current_site(request).name,
+            'object': content_object,
+        }
+        message = t.render(c)
+        send_mail(subject, message, settings.DEFAULT_FROM_EMAIL, recipient_list, fail_silently=True)
+
+
+class Moderator(object):
+    """
+    Handles moderation of a set of models.
+
+    An instance of this class will maintain a list of one or more
+    models registered for comment moderation, and their associated
+    moderation classes, and apply moderation to all incoming comments.
+
+    To register a model, obtain an instance of ``Moderator`` (this
+    module exports one as ``moderator``), and call its ``register``
+    method, passing the model class and a moderation class (which
+    should be a subclass of ``CommentModerator``). Note that both of
+    these should be the actual classes, not instances of the classes.
+
+    To cease moderation for a model, call the ``unregister`` method,
+    passing the model class.
+
+    For convenience, both ``register`` and ``unregister`` can also
+    accept a list of model classes in place of a single model; this
+    allows easier registration of multiple models with the same
+    ``CommentModerator`` class.
+
+    The actual moderation is applied in two phases: one prior to
+    saving a new comment, and the other immediately after saving. The
+    pre-save moderation may mark a comment as non-public or mark it to
+    be removed; the post-save moderation may delete a comment which
+    was disallowed (there is currently no way to prevent the comment
+    being saved once before removal) and, if the comment is still
+    around, will send any notification emails the comment generated.
+
+    """
+
+    def __init__(self):
+        self._registry = {}
+        self.connect()
+
+    def connect(self):
+        """
+        Hook up the moderation methods to pre- and post-save signals
+        from the comment models.
+
+        """
+        signals.comment_will_be_posted.connect(self.pre_save_moderation, sender=django_comments.get_model())
+        signals.comment_was_posted.connect(self.post_save_moderation, sender=django_comments.get_model())
+
+    def register(self, model_or_iterable, moderation_class):
+        """
+        Register a model or a list of models for comment moderation,
+        using a particular moderation class.
+
+        Raise ``AlreadyModerated`` if any of the models are already
+        registered.
+
+        """
+        if isinstance(model_or_iterable, ModelBase):
+            model_or_iterable = [model_or_iterable]
+        for model in model_or_iterable:
+            if model in self._registry:
+                raise AlreadyModerated("The model '%s' is already being moderated" % model._meta.model_name)
+            self._registry[model] = moderation_class(model)
+
+    def unregister(self, model_or_iterable):
+        """
+        Remove a model or a list of models from the list of models
+        whose comments will be moderated.
+
+        Raise ``NotModerated`` if any of the models are not currently
+        registered for moderation.
+
+        """
+        if isinstance(model_or_iterable, ModelBase):
+            model_or_iterable = [model_or_iterable]
+        for model in model_or_iterable:
+            if model not in self._registry:
+                raise NotModerated("The model '%s' is not currently being moderated" % model._meta.model_name)
+            del self._registry[model]
+
+    def pre_save_moderation(self, sender, comment, request, **kwargs):
+        """
+        Apply any necessary pre-save moderation steps to new
+        comments.
+
+        """
+        model = comment.content_type.model_class()
+        if model not in self._registry:
+            return
+        content_object = comment.content_object
+        moderation_class = self._registry[model]
+
+        # Comment will be disallowed outright (HTTP 403 response)
+        if not moderation_class.allow(comment, content_object, request):
+            return False
+
+        if moderation_class.moderate(comment, content_object, request):
+            comment.is_public = False
+
+    def post_save_moderation(self, sender, comment, request, **kwargs):
+        """
+        Apply any necessary post-save moderation steps to new
+        comments.
+
+        """
+        model = comment.content_type.model_class()
+        if model not in self._registry:
+            return
+        self._registry[model].email(comment, comment.content_object, request)
+
+# Import this instance in your own code to use in registering
+# your models for moderation.
+moderator = Moderator()