Refactor CommentTree collapsing a little

This is being done to be able to support some other collapsing behavior
starting to come in (for example, as an effect from comment tags).
However, it's starting to get pretty ugly at this point. I should
probably try to implement a wrapper class for Comments that are inside a
CommentTree so that I can move methods like this into that class instead
of needing them to be staticmethods on the CommentTree class itself.

tildes/tildes/models/comment/comment_tree.py

@@ -195,41 +195,46 @@ class CommentTree:
             comment.collapsed_state = "uncollapsed"
 
             # fetch its direct parent and uncollapse it as well
-            parent_comment: Optional[Comment] = None
             if comment.parent_comment_id:
                 parent_comment = self.comments_by_id[comment.parent_comment_id]
                 parent_comment.collapsed_state = "uncollapsed"
 
-            # then follow parents to the root, individually collapsing them all
-            while parent_comment:
-                if not parent_comment.collapsed_state:
-                    parent_comment.collapsed_state = "individual"
+    @staticmethod
+    def _has_uncollapsed_descendant(comment: Comment) -> bool:
+        """Recursively check if the comment has an uncollapsed descendant."""
+        for reply in comment.replies:
+            if reply.collapsed_state == "uncollapsed":
+                return True
 
-                if parent_comment.parent_comment_id:
-                    parent_comment = self.comments_by_id[
-                        parent_comment.parent_comment_id
-                    ]
-                else:
-                    parent_comment = None
+            if CommentTree._has_uncollapsed_descendant(reply):
+                return True
 
-        self._finalize_collapsing()
+        return False
 
-    def _finalize_collapsing(self) -> None:
-        """Finish collapsing that was done partially by a different method."""
-        # if all the comments would end up collapsed, leave them all uncollapsed
-        if all([comment.collapsed_state is None for comment in self.comments]):
+    @staticmethod
+    def _recursively_collapse(comment: Comment) -> None:
+        """Recursively collapse a comment and its replies as much as possible."""
+        # stop processing the branch as soon as we hit an uncollapsed comment
+        if comment.collapsed_state == "uncollapsed":
+            return
+
+        # if it doesn't have any uncollapsed descendants, collapse the whole branch
+        # and stop looking any deeper into it
+        if not CommentTree._has_uncollapsed_descendant(comment):
+            comment.collapsed_state = "full"
             return
 
-        # go over each top-level comment and go into each branch depth-first. Any
-        # comment that still has its state as None can be fully collapsed (and we can
-        # stop looking down that branch)
-        def recursively_collapse(comment: Comment) -> None:
-            if not comment.collapsed_state:
-                comment.collapsed_state = "full"
-                return
+        # otherwise (does have uncollapsed descendant), collapse this comment
+        # individually and recurse into all branches underneath it
+        comment.collapsed_state = "individual"
+        for reply in comment.replies:
+            CommentTree._recursively_collapse(reply)
 
-            for reply in comment.replies:
-                recursively_collapse(reply)
+    def finalize_collapsing_maximized(self) -> None:
+        """Finish collapsing comments, collapsing as much as possible."""
+        # if no comments have their state defined, leave them all uncollapsed
+        if all([comment.collapsed_state is None for comment in self.comments]):
+            return
 
         for comment in self.tree:
-            recursively_collapse(comment)
+            self._recursively_collapse(comment)

tildes/tildes/views/topic.py

@@ -288,6 +288,7 @@ def get_topic(request: Request, comment_order: CommentSortOption) -> dict:
         # (and doesn't have that behavior disabled)
         if topic.last_visit_time and request.user.collapse_old_comments:
             tree.collapse_old_comments(topic.last_visit_time)
+            tree.finalize_collapsing_maximized()
 
     return {
         "topic": topic,