+            return rc.NOT_FOUND
+
+
+# add categorized tags fields for Book
+def _tags_getter(category):
+    @classmethod
+    def get_tags(cls, book):
+        return book.tags.filter(category=category)
+    return get_tags
+for plural, singular in category_singular.items():
+    setattr(BookDetails, plural, _tags_getter(singular))
+
+# add fields for files in Book
+def _file_getter(format):
+    field = "%s_file" % format
+    @classmethod
+    def get_file(cls, book):
+        f = getattr(book, field)
+        if f:
+            return MEDIA_BASE + f.url
+        else:
+            return ''
+    return get_file
+for format in Book.formats:
+    setattr(BookDetails, format, _file_getter(format))
+
+
+class TagDetails(object):
+    """Custom Tag fields."""
+
+    @classmethod
+    def href(cls, tag):
+        """ Returns URI in the API for the tag. """
+
+        return API_BASE + reverse("api_tag", args=[category_plural[tag.category], tag.slug])
+
+    @classmethod
+    def url(cls, tag):
+        """ Returns URL on the site. """
+
+        return WL_BASE + tag.get_absolute_url()
+
+
+class TagDetailHandler(BaseHandler, TagDetails):
+    """ Responsible for details of a single Tag object. """
+
+    fields = ['name', 'url', 'sort_key', 'description']
+
+    @piwik_track
+    def read(self, request, category, slug):
+        """ Returns details of a tag, identified by category and slug. """
+
+        try:
+            category_sng = category_singular[category]
+        except KeyError, e:
+            return rc.NOT_FOUND
+
+        try:
+            return Tag.objects.get(category=category_sng, slug=slug)
+        except Tag.DoesNotExist:
+            return rc.NOT_FOUND
+
+
+class TagsHandler(BaseHandler, TagDetails):
+    """ Main handler for Tag objects.
+
+    Responsible for lists of Tag objects
+    and fields used for representing Tags.
+
+    """
+    allowed_methods = ('GET',)
+    model = Tag
+    fields = ['name', 'href', 'url']
+
+    @piwik_track
+    def read(self, request, category):
+        """ Lists all tags in the category (eg. all themes). """
+
+        try:
+            category_sng = category_singular[category]
+        except KeyError, e:
+            return rc.NOT_FOUND
+
+        tags = Tag.objects.filter(category=category_sng).exclude(book_count=0)
+        if tags.exists():
+            return tags
+        else:
+            return rc.NOT_FOUND
+
+
+class FragmentDetails(object):
+    """Custom Fragment fields."""
+
+    @classmethod
+    def href(cls, fragment):
+        """ Returns URI in the API for the fragment. """
+
+        return API_BASE + reverse("api_fragment", 
+            args=[fragment.book.slug, fragment.anchor])
+
+    @classmethod
+    def url(cls, fragment):
+        """ Returns URL on the site for the fragment. """
+
+        return WL_BASE + fragment.get_absolute_url()
+
+    @classmethod
+    def themes(cls, fragment):
+        """ Returns a list of theme tags for the fragment. """
+
+        return fragment.tags.filter(category='theme')
+
+
+class FragmentDetailHandler(BaseHandler, FragmentDetails):
+    fields = ['book', 'anchor', 'text', 'url', 'themes']
+
+    @piwik_track
+    def read(self, request, book, anchor):
+        """ Returns details of a fragment, identified by book slug and anchor. """
+        try:
+            return Fragment.objects.get(book__slug=book, anchor=anchor)
+        except Fragment.DoesNotExist:
+            return rc.NOT_FOUND
+
+
+class FragmentsHandler(BaseHandler, FragmentDetails):
+    """ Main handler for Fragments.
+
+    Responsible for lists of Fragment objects
+    and fields used for representing Fragments.
+
+    """
+    model = Fragment
+    fields = ['book', 'url', 'anchor', 'href']
+    allowed_methods = ('GET',)
+
+    categories = set(['author', 'epoch', 'kind', 'genre', 'book', 'theme'])
+
+    @piwik_track
+    def read(self, request, tags):
+        """ Lists all fragments with given book, tags, themes.
+
+        :param tags: should be a path of categories and slugs, i.e.:
+             books/book-slug/authors/an-author/themes/a-theme/
+
+        """
+        try:
+            tags = read_tags(tags, allowed=self.categories)
+        except ValueError:
+            return rc.NOT_FOUND
+        fragments = Fragment.tagged.with_all(tags).select_related('book')
+        if fragments.exists():
+            return fragments
+        else:
+            return rc.NOT_FOUND
+
+
+
+# Changes handlers
+
+class CatalogueHandler(BaseHandler):
+
+    @staticmethod
+    def fields(request, name):
+        fields_str = request.GET.get(name) if request is not None else None
+        return fields_str.split(',') if fields_str is not None else None
+
+    @staticmethod
+    def until(t=None):
+        """ Returns time suitable for use as upper time boundary for check.
+
+            Used to avoid issues with time between setting the change stamp
+            and actually saving the model in database.
+            Cuts the microsecond part to avoid issues with DBs where time has
+            more precision.
+
+            :param datetime t: manually sets the upper boundary
+
+        """
+        # set to five minutes ago, to avoid concurrency issues
+        if t is None:
+            t = datetime.now() - timedelta(seconds=settings.API_WAIT)
+        # set to whole second in case DB supports something smaller
+        return t.replace(microsecond=0)
+
+    @staticmethod
+    def book_dict(book, fields=None):
+        all_fields = ['url', 'title', 'description',
+                      'gazeta_link', 'wiki_link',
+                      ] + Book.formats + BookMedia.formats + [
+                      'parent', 'parent_number',
+                      'tags',
+                      'license', 'license_description', 'source_name',
+                      'technical_editors', 'editors',
+                      'author', 'sort_key',
+                     ]
+        if fields:
+            fields = (f for f in fields if f in all_fields)
+        else:
+            fields = all_fields
+
+        extra_info = book.get_extra_info_value()
+
+        obj = {}
+        for field in fields:
+
+            if field in Book.formats:
+                f = getattr(book, field+'_file')
+                if f:
+                    obj[field] = {
+                        'url': f.url,
+                        'size': f.size,
+                    }
+
+            elif field in BookMedia.formats:
+                media = []
+                for m in book.media.filter(type=field):
+                    media.append({
+                        'url': m.file.url,
+                        'size': m.file.size,
+                    })
+                if media:
+                    obj[field] = media
+
+            elif field == 'url':
+                obj[field] = book.get_absolute_url()
+
+            elif field == 'tags':
+                obj[field] = [t.id for t in book.tags.exclude(category__in=('book', 'set'))]
+
+            elif field == 'author':
+                obj[field] = ", ".join(t.name for t in book.tags.filter(category='author'))
+
+            elif field == 'parent':
+                obj[field] = book.parent_id
+
+            elif field in ('license', 'license_description', 'source_name',
+                      'technical_editors', 'editors'):
+                f = extra_info.get(field)
+                if f:
+                    obj[field] = f
+
+            else:
+                f = getattr(book, field)
+                if f:
+                    obj[field] = f
+
+        obj['id'] = book.id
+        return obj
+
+    @classmethod
+    def book_changes(cls, request=None, since=0, until=None, fields=None):
+        since = datetime.fromtimestamp(int(since))
+        until = cls.until(until)
+
+        changes = {
+            'time_checked': timestamp(until)
+        }
+
+        if not fields:
+            fields = cls.fields(request, 'book_fields')
+
+        added = []
+        updated = []
+        deleted = []
+
+        last_change = since
+        for book in Book.objects.filter(changed_at__gte=since,
+                    changed_at__lt=until):
+            book_d = cls.book_dict(book, fields)
+            updated.append(book_d)
+        if updated:
+            changes['updated'] = updated
+
+        for book in Deleted.objects.filter(content_type=Book, 
+                    deleted_at__gte=since,
+                    deleted_at__lt=until,
+                    created_at__lt=since):
+            deleted.append(book.id)
+        if deleted:
+            changes['deleted'] = deleted
+
+        return changes
+
+    @staticmethod
+    def tag_dict(tag, fields=None):
+        all_fields = ('name', 'category', 'sort_key', 'description',
+                      'gazeta_link', 'wiki_link',
+                      'url', 'books',
+                     )