Define the get_cover_url() method

recipes/fokus.recipe

@@ -2,6 +2,9 @@
 # vim:fileencoding=utf-8
 from datetime import datetime, timezone
 
+from mechanize import Request
+
+from calibre.ebooks.BeautifulSoup import BeautifulSoup
 from calibre.web.feeds.news import BasicNewsRecipe
 
 
@@ -67,6 +70,31 @@ class Fokus(BasicNewsRecipe):
         dict(name='div', class_='wp-block-core-paragraph'),
     ]
 
+    def get_cover_url(self) -> str:
+        # Create a `mechanize.Request` object.
+        req = Request(url=self.main_url, method='POST')
+
+        # Open the requested URL in the built-in browser of the `BasicNewsRecipe` parent class.
+        browser = self.get_browser()
+        response = browser.open(req)
+
+        # Parse the response into a BeautifulSoup soup.
+        soup = BeautifulSoup(response.get_data(), "html.parser")
+
+        # The cover image of the current edition is located in a <figure> tag with class 'Issue__thumbnail'.
+        try:
+            figure_tag = soup.find('figure', class_='Issue__thumbnail')
+            img_tag = figure_tag.find('img')
+            # Set the `img_tag` to `None` if it is falsy. This way, we can force an `AttributeError` if no cover URL
+            # can be found.
+            img_tag = img_tag if img_tag else None
+            cover_url = img_tag["src"]
+        except AttributeError:
+            self.log.error("Failed to identify the cover image URL. Does an 'Issue__thumbnail' figure still exist?")
+            return ''
+
+        return cover_url
+
     def get_browser(self):
         br = BasicNewsRecipe.get_browser(self)
         if self.username and self.password: