# -*- coding: utf-8 -*-
"""
# HOTP/TOTP support
# Copyright (c) 2019-2024 Michael Büsch <m@bues.ch>
# Licensed under the GNU/GPL version 2 or later.
"""

import time
from base64 import b32decode
import binascii
import hmac
import hashlib

__all__ = [
	"OtpError",
	"hotp",
	"totp",
]

class OtpError(Exception):
	"""HOTP/TOTP exception.
	"""

def hotp(key, counter, nrDigits=6, hmacHash="SHA1"):
	"""HOTP - An HMAC-Based One-Time Password Algorithm.
	key: The HOTP key. Either raw bytes or a base32 encoded string.
	counter: The HOTP counter integer.
	nrDigits: The number of digits to return. Can be 1 to 8.
	hmacHash: The name string of the hashing algorithm.
	Returns the calculated HOTP token string.
	"""
	if isinstance(key, str):
		try:
			key = b32decode(key.encode("UTF-8"), casefold=True)
		except (binascii.Error, UnicodeError):
			raise OtpError("Invalid key.")
	if not (0 <= counter <= (2 ** 64) - 1):
		raise OtpError("Invalid counter.")
	if not (1 <= nrDigits <= 8):
		raise OtpError("Invalid number of digits.")
	try:
		hmacHash = hmacHash.replace("-", "")
		hmacHash = hmacHash.replace("_", "")
		hmacHash = hmacHash.replace(" ", "")
		hmacHash = hmacHash.upper().strip()
		hmacHash = {
			"SHA1"   : hashlib.sha1,
			"SHA256" : hashlib.sha256,
			"SHA512" : hashlib.sha512,
		}[hmacHash]
	except KeyError:
		raise OtpError("Invalid HMAC hash type.")

	counter = counter.to_bytes(length=8, byteorder="big", signed=False)
	h = bytearray(hmac.new(key, counter, hmacHash).digest())
	offset = h[19] & 0xF
	h[offset] &= 0x7F
	hSlice = int.from_bytes(h[offset:offset+4], byteorder="big", signed=False)
	otp = hSlice % (10 ** nrDigits)
	fmt = "%0" + str(nrDigits) + "d"
	return fmt % otp

def totp(key, nrDigits=6, hmacHash="SHA1", t=None):
	"""TOTP - Time-Based One-Time Password Algorithm.
	nrDigits: The number of digits to return. Can be 1 to 8.
	hmacHash: The name string of the hashing algorithm.
	t: Optional; the time in seconds. Uses time.time(), if not given.
	Returns the calculated TOTP token string.
	"""
	if t is None:
		t = time.time()
	t = (int(round(t)) // 30) - 1
	return hotp(key, t, nrDigits, hmacHash)