def valid_channel_name(name):
	"""Channel names can only contain lowercase letters,
	numbers, hyphens, and underscores, and must be 21 characters or less.

	Some sample conversions from Slack to determine some heuristics:
		1..................20abc def => 1_20abc-def
		1..................20abc..def => 1_20abc_def

	Heuristics:
		1. Encode input into ASCII
		2. Replace non-alphanumeric groups of charaters by a single _
		3. Replace all spaces by dashes
		4. Truncate the resulting sring into first 21 characters
	"""
	result = unicodedata.normalize('NFD', name).encode('ascii', 'ignore')
	result = re.sub("[^a-zA-Z\d\s-]+", '_', result)
	result = result.replace(' ', '-')
	result = result[:21].lower()
	return result