import base64
import hashlib

import entry

class KnownHostsSyntaxError(Exception): pass

class HashedHostError(Exception): pass

def process_line(line):
	"""process_line(str) → [Entry]
	Given a string containing one line of .ssh/known_hosts file, create
	a list of Entries based on it."""
	assert type(line) == str

	# Remove trailing newlines
	if line[-1] == '\n': line = line[:-1]

	# Just skip over empty lines
	if line == '': return []

	# Each line has host(s), algorithm, public key, and possibly one
	# more optional field
	fields = line.split(' ')
	if len(fields) != 3 and len(fields) != 4:
		raise KnownHostsSyntaxError('Weird number of fields on a line (%i)' % len(fields))

	hosts, algorithm, public_key = fields[0:3]

	# Generate public key fingerprint
	# The key is stored base64 encoded, so decode it first
	try:
		public_key_binary = base64.b64decode(public_key, validate = True)
	except (ValueError, base64.binascii.Error) as err:
		raise KnownHostsSyntaxError('Malformed public key: %s' % public_key) from err
	
	# Fingerprint is sha256 hash of the public key
	m = hashlib.sha256()
	m.update(public_key_binary)
	fingerprint = m.digest()

	# There can be several hosts separated with a comma
	entries = []
	for host in hosts.split(','):
		# A host can't be empty
		if len(host) == 0:
			raise KnownHostsSyntaxError('An empty host')

		# If the host begins with '|' it's hashed
		# We cannot deal with those
		if host[0] == '|':
			raise HashedHostError('Cannot deal with hashed hosts')

		# If the host behins with '[' it's a nonstandard port
		# The format will be [domain]:port
		# Extractt both
		# Otherwise, default to port 22
		if host[0] == '[':
			host_and_port = host[1:].split(']:')
			if len(host_and_port) != 2:
				raise KnownHostsSyntaxError('Unrecognized host format: ' + host)

			domain = host_and_port[0]
			try:
				port = int(host_and_port[1])
			except ValueError:
				raise KnownHostsSyntaxError('Malformed port: %i' % port)

		else:
			domain = host
			port = 22

		# Default to no comment
		entries.append(entry.create_entry(domain, port, fingerprint, ''))

	return entries