Video preview descriptions truncated to avoid API errors

rocketbot/cogs/videopreviewcog.py

 	blockquote_markdown,
 	format_bytes,
 	suppress_markdown_url_previews,
+	truncate_markdown,
 )
 
 
 			link_description += f", {format_bytes(best_format.get('filesize_approx'))}"
 		content = "Here's a preview of that video link."
 		if len(description) > 0:
+			description = truncate_markdown(description, 1000)
 			content += "\n\n" + blockquote_markdown(suppress_markdown_url_previews(description)) + "\n"
 		if link.spoiler:
 			content += f"\n||[{link_description}]({video_url})||"

rocketbot/utils.py

 	"""Finds URLs in markdown and encloses them in <...> to suppress the preview."""
 	return re.sub(r'(?<!<)(https?://\S+)(?!>)', '<\\1>', markdown)
 
+def truncate_markdown(markdown: str, max_length: int) -> str:
+	"""Truncates markdown in a way that attempts to minimize formatting disruption."""
+	if len(markdown) <= max_length:
+		return markdown
+	markdown = markdown[:max_length]
+
+	# Try to cut at a newline if it's in the latter 20% of the max length
+	last_newline_index = markdown.rfind('\n')
+	if last_newline_index >= 0 and last_newline_index < (max_length * 8 / 10):
+		return markdown[:last_newline_index] + "\n\u2026"
+
+	# Cut at the last space
+	last_space_index = markdown.rfind(' ')
+	if last_space_index >= 0:
+		return markdown[:last_space_index] + " \u2026"
+
+	# Last resort, do a blind substring
+	return markdown[:max_length - 1] + "\u2026"
+
 def format_bytes(size: int) -> str:
 	"""Formats s size in bytes to a human readable description (e.g. "3.2 KiB")"""
 	size = max(size, 0)