+ s = force_unicode(s)
+ length = int(num)
+ if length <= 0:
+ return u''
+ html4_singlets = ('br', 'col', 'link', 'base', 'img', 'param', 'area', 'hr', 'input')
+ # Set up regular expressions
+ re_words = re.compile(r'&.*?;|<.*?>|(\w[\w-]*)', re.U)
+ re_tag = re.compile(r'<(/)?([^ ]+?)(?: (/)| .*?)?>')
+ # Count non-HTML words and keep note of open tags
+ pos = 0
+ end_text_pos = 0
+ words = 0
+ open_tags = []
+ while words <= length:
+ m = re_words.search(s, pos)
+ if not m:
+ # Checked through whole string
+ break
+ pos = m.end(0)
+ if m.group(1):
+ # It's an actual non-HTML word
+ words += 1
+ if words == length:
+ end_text_pos = pos
+ continue
+ # Check for tag
+ tag = re_tag.match(m.group(0))
+ if not tag or end_text_pos:
+ # Don't worry about non tags or tags after our truncate point
+ continue
+ closing_tag, tagname, self_closing = tag.groups()
+ tagname = tagname.lower() # Element names are always case-insensitive
+ if self_closing or tagname in html4_singlets:
+ pass
+ elif closing_tag:
+ # Check for match in open tags list
+ try:
+ i = open_tags.index(tagname)
+ except ValueError:
+ pass
+ else:
+ # SGML: An end tag closes, back to the matching start tag, all unclosed intervening start tags with omitted end tags
+ open_tags = open_tags[i+1:]
+ else:
+ # Add it to the start of the open tags list
+ open_tags.insert(0, tagname)
+ if words <= length:
+ # Don't try to close tags if we don't need to truncate
+ return s
+ out = s[:end_text_pos]
+ if end_text:
+ out += end_text
+ # Close any tags still open
+ for tag in open_tags:
+ out += '</%s>' % tag
+ # Return string
+ return out
+
+
+def customizations_hash(customizations):
+ customizations.sort()
+ return hash(tuple(customizations))
+
+
+def get_customized_pdf_path(book, customizations):
+ """
+ Returns a MEDIA_ROOT relative path for a customized pdf. The name will contain a hash of customization options.
+ """
+ h = customizations_hash(customizations)
+ return 'book/%s/%s-custom-%s.pdf' % (book.slug, book.slug, h)
+
+
+def clear_custom_pdf(book):
+ """
+ Returns a list of paths to generated customized pdf of a book
+ """
+ from waiter.utils import clear_cache
+ clear_cache('book/%s' % book.slug)
+
+
+class AppSettings(object):
+ """Allows specyfying custom settings for an app, with default values.
+
+ Just subclass, set some properties and instantiate with a prefix.
+ Getting a SETTING from an instance will check for prefix_SETTING
+ in project settings if set, else take the default. The value will be
+ then filtered through _more_SETTING method, if there is one.
+