use the LWN weekly publication date

Bulk conversion (unfortunately) is a frequent thing when catching up
after a holiday or crontab breakage. It is really annoying figuring out
the LWN weekly edition reading order if they all have the same title
based on the conversion date.

Falls back to the current date if the date cannot be parsed.

Uses dateutil.parser.parse() for thread-safety.

recipes/lwn_weekly.recipe

@@ -12,6 +12,7 @@ import re
 import sys
 
 from calibre.web.feeds.news import BasicNewsRecipe
+from calibre.utils.date import now as nowf
 
 
 class WeeklyLWN(BasicNewsRecipe):
@@ -82,6 +83,19 @@ class WeeklyLWN(BasicNewsRecipe):
 
         return url
 
+    def publication_date(self):
+        return self.pub_date
+
+    def parse_publication_date(self, soup):
+        from dateutil.parser import parse, ParserError
+        try:
+            date_match = re.match(r'.* +for +([^\[]*)', self.tag_to_string(soup.head.title.string))
+            # dateutil.parser.parse() is considered thread-safe
+            self.pub_date = parse(date_match[1])
+        except (TypeError, ParserError):
+            self.log.warning('Failed to parse publication date from title: %r, using current time' % soup.head.title.string)
+            self.pub_date = nowf()
+
     def parse_index(self):
         past_edition = self.recipe_specific_options.get('issue')
         if past_edition and isinstance(past_edition, str):
@@ -91,6 +105,7 @@ class WeeklyLWN(BasicNewsRecipe):
         else:
             index_url = self.print_version('/free/bigpage')
         soup = self.index_to_soup(index_url)
+        self.parse_publication_date(soup)
         curr = soup.body
 
         articles = {}