Display published date on link topics if old

Uses the "published" time from the Embedly data to display the date that
a link was published if it was more than 3 days before the link topic
was submitted.

tildes/tildes/lib/datetime.py

@@ -79,6 +79,11 @@ def utc_now() -> datetime:
     return datetime.now(timezone.utc)
 
 
+def utc_from_timestamp(timestamp: int) -> datetime:
+    """Return timezone-aware datetime from a UTC timestamp."""
+    return datetime.fromtimestamp(timestamp, timezone.utc)
+
+
 def descriptive_timedelta(target: datetime, abbreviate: bool = False) -> str:
     """Return a descriptive string for how long ago a datetime was.
 

tildes/tildes/models/topic/topic.py

@@ -27,7 +27,7 @@ from titlecase import titlecase
 
 from tildes.enums import TopicType
 from tildes.lib.database import ArrayOfLtree
-from tildes.lib.datetime import utc_now
+from tildes.lib.datetime import utc_from_timestamp, utc_now
 from tildes.lib.id import id_to_id36
 from tildes.lib.markdown import convert_markdown_to_safe_html
 from tildes.lib.string import convert_to_url_slug
@@ -363,6 +363,7 @@ class Topic(DatabaseModel):
     @property
     def content_metadata_for_display(self) -> str:
         """Return a string of the content's metadata, suitable for display."""
+        # pylint: disable=too-many-branches
         metadata_strings = []
 
         if self.is_text_type:
@@ -375,6 +376,13 @@ class Topic(DatabaseModel):
         elif self.is_link_type:
             metadata_strings.append(f"{self.link_domain}")
 
+            # display the published date if it's more than 3 days before the topic
+            published_timestamp = self.get_content_metadata("published")
+            if published_timestamp:
+                published = utc_from_timestamp(published_timestamp)
+                if self.created_time - published > timedelta(days=3):
+                    metadata_strings.append(published.strftime("%b %-d %Y"))
+
         return ", ".join(metadata_strings)
 
     @property