from collections import namedtuple

import hashing

# Entry(bytes[32], bytes[32], bytes[32], bytes[0…2¹⁶-1])
Entry = namedtuple('Entry', ['salt', 'hashed_host', 'fingerprint', 'comment'])

class UnacceptableComment(Exception): pass

def create_entry(domain, port, fingerprint, comment):
	"""create_entry(str, u16, bytes[32], str) → Entry
	Given unprocessed host, a binary fingerprint and a comment, creates
	and entry describing it"""
	assert type(domain) == str
	assert type(port) == int and 0 <= port <= (1<<16) - 1
	assert type(fingerprint) == bytes and len(fingerprint) == 32
	assert type(comment) == str

	# We want to have domain names reasonably normalized. This is why we
	# convert all internationalized domain names to punycode and
	# lowercase all domains.
	# The reason the lowercasing happens after the punycoding is because
	# that way we don't have to worry about Unicode case mapping: in
	# case of IDN the IDNA codec handles that for us, and in case of an
	# ASCII domain it passes through the IDNA unmodified
	processed_host = domain.encode('idna').lower()

	# If the port is not :22, we store [host]:port instead
	if port != 22:
		processed_host = b'[%s]%i' % (processed_host, port)

	# Hash the host and store the salt
	salt, hashed_host = hashing.hash_host(processed_host)

	# Comment must not include newlines
	if '\n' in comment:
		raise UnacceptableComment('Comment contains newlines')

	comment_encoded = comment.encode('utf-8')

	# Comment may be at max 2¹⁶-1 bytes long
	if len(comment_encoded) >= 1<<16:
		raise UnacceptableComment('Comment length of %i bytes is too long' % len(comment_encoded))

	return Entry(salt, hashed_host, fingerprint, comment_encoded)