import entry

class FileFormatError(Exception): pass

class VersionMismatch(Exception): pass

def check_header(f):
	"""check_header(file(rb))
	Throw an error if the header isn't good"""
	# Magic is b'WOT'
	magic = f.read(3)
	if magic != b'WOT':
		raise FileFormatError('Invalid magic')

	# Version 0 is the current one
	version = f.read(1)
	if version == b'':
		raise FileFormatError('Unexpected end of file')
	if version != b'\0':
		raise VersionMismatch('Version %i not supported' % version[0])

def read_entry(f):
	"""read_entry(file(rb)) → Entry / None
	Returns None if the end of file has been reached"""
	# u8[32]: salt
	salt = f.read(32)
	if len(salt) == 0:
		# End of file has been reached, return None to mark that
		return None
	elif len(salt) != 32:
		raise FileFormatError('Unexpected end of file')

	# u8[32]: hashed_host
	hashed_host = f.read(32)
	if len(hashed_host) != 32:
		raise FileFormatError('Unexpected end of file')

	# u8[32]: fingerprint
	fingerprint = f.read(32)
	if len(fingerprint) != 32:
		raise FileFormatError('Unexpected end of file')

	# u16le: comment_length
	length_bytes = f.read(2)
	if len(length_bytes) != 2:
		raise FileFormatError('Unexpected end of file')
	comment_length = length_bytes[0] | length_bytes[1] << 8

	# u8[comment_length]: comment
	comment = f.read(comment_length)
	if len(comment) != comment_length:
		raise FileFormatError('Unexpected end of file')

	return entry.Entry(salt, hashed_host, fingerprint, comment)

def read(f):
	"""read_file(file(rb)) → [Entry]"""
	check_header(f)

	entries = []
	while True:
		# Read until we reach the end of file
		entry = read_entry(f)
		if entry is None: break
		entries.append(entry)

	return entries