#! /usr/bin/env python3

# Yandere Lewd Bot, an image posting bot for Pleroma
# Copyright (C) 2022 Anon <yanderefedi@proton.me>
# 
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

import sys
import base64
import os
import getpass
from cryptography.fernet import Fernet, InvalidToken
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC

from collections import OrderedDict


class PasswordMismatch(Exception):
	pass


# Salts
def generate_salt():
	return os.urandom(16)


# Return string from bytes
def salt_encode(b):
	return base64.urlsafe_b64encode(b).decode()


# Return bytes from string
def salt_decode(s):
	return base64.urlsafe_b64decode(s.encode())


# Ordered Dictionaries
def change_encoding_dict(settings_server, encoding_type):
	return OrderedDict([(k, encoding_type(v)) for k, v in settings_server.items()])


# Return bytes from string
def encode_dict(settings_server):
	return change_encoding_dict(settings_server, str.encode)


# Return string from bytes
def decode_dict(settings_server):
	return change_encoding_dict(settings_server, bytes.decode)


# password: Bytes
# salt: Bytes
def derive_key(password, salt):
	kdf = PBKDF2HMAC(
		algorithm=hashes.SHA256(),
		length=32,
		salt=salt,
		iterations=100000,
		backend=default_backend()
		)
	r_key = base64.urlsafe_b64encode(kdf.derive(password))
	return r_key


# Encryption functions
# message: Bytes
# key: Bytes
def encrypt(message, key):
	f = Fernet(key)
	token = f.encrypt(message)
	return token


# token: Bytes
# key: Bytes
def decrypt(token, key):
	f = Fernet(key)
	message = f.decrypt(token)
	return message


# password: 			bytes()
# salt: 				bytes()
# settings_server: 		dict() -> Byte values
# encryption_function:	encrypt(message, key) : decrypt(token, key):
# Returns settings_server_decrypted dictionary with Byte() values. Will need to use
# ChangeEncodingDict to make them strings (recommended cfg file friendly)
def __settings_server(password, salt, settings_server, encryption_function):
	key = derive_key(password, salt)
	settings_server_decrypted = OrderedDict()
	for setting in settings_server:
		settings_server_decrypted[setting] = encryption_function(settings_server[setting], key)
	return settings_server_decrypted


# Returns (salt, settings_server)
def _settings_server_encrypt(settings_server):
	salt = generate_salt()
	password = getpass.getpass("Enter password: ")
	password2 = getpass.getpass("Retype Password: ")

	if password != password2:
		raise PasswordMismatch

	settings_server_encrypted = __settings_server(password.encode(), salt, encode_dict(settings_server), encrypt)

	return salt, settings_server_encrypted


# Returns (settings_server)
def _settings_server_decrypt(settings_server, settings_encrypt):
	settings_server_encoded = encode_dict(settings_server)
	if settings_encrypt["encrypt"]:
		salt = salt_decode(settings_encrypt["salt"])
		password = getpass.getpass("Enter password: ")
		return __settings_server(password.encode(), salt, settings_server_encoded, decrypt)
	else:
		return settings_server_encoded


# Wrapper function that will catch exceptions and exit
def settings_server_new(function, **kwargs):
	try:
		return function(**kwargs)

	# If the user cancels the login
	except KeyboardInterrupt:
		print("\nQuitting...")

	# If the user passwords do not match (encrypt)
	except PasswordMismatch:
		print("Passwords do not match...")

	# Incorrect password entered (decrypt)
	except InvalidToken:
		print("Password or Token Incorrect...")

	# Probably the salt value got modified
	except base64.binascii.Error:
		print("Salt is invalid...")

	# Some other kind of fuck up
	except Exception as e:
		print("Unknown exception occurred...")
		print(e)

	# Exit if an exception was thrown
	sys.exit(1)


# Glue functions that package **kwargs automatically
def settings_server_encrypt(settings_server):
	kwargs = {"settings_server": settings_server}
	return settings_server_new(_settings_server_encrypt, **kwargs)


def settings_server_decrypt(settings_server, settings_encrypt):
	kwargs = {
			"settings_server": settings_server,
			"settings_encrypt": settings_encrypt
			}
	return settings_server_new(_settings_server_decrypt, **kwargs)


# The _cfg functions should return a regular string
# These are the functions that should interface with the bot a return a plain string
# settings_server ordered dictionary
def settings_server_encrypt_cfg(settings_server):
	salt, settings_server = settings_server_encrypt(settings_server)
	return salt_encode(salt), decode_dict(settings_server)


def settings_server_decrypt_cfg(settings_server, settings_encrypt):
	settings_server = settings_server_decrypt(settings_server, settings_encrypt)
	return decode_dict(settings_server)


def main():
	import argparse
	from pprint import pformat

	default_cfg = "cfg"

	parser = argparse.ArgumentParser(
									description="A class to encrypt server credentials",
									epilog="There are no additional parameters.",
									add_help=True	)
	parser.add_argument("--encrypt", help="Generate encrypted authentication.", action="store_true")
	parser.add_argument("--decrypt", help="Decrypt encrypted authentication", action="store_true")
	parser.add_argument("--recrypt", help="Recrypt encrypted authentication", action="store_true")
	parser.add_argument("-c", "--cfg", help="Specify config file.", default=default_cfg)

	arguments = parser.parse_args()

	if arguments.recrypt:
		arguments.encrypt = True
		arguments.decrypt = True

	if arguments.encrypt or arguments.decrypt:
		import importlib
		cfg = importlib.import_module(arguments.cfg)
		settings_server = cfg.settings_server
		settings_encrypt = None

		if arguments.decrypt and arguments.encrypt:
			print("Re-encrypting")

		if arguments.decrypt:		# arguments.decrypt
			print("Decrypt...")
			settings_server = settings_server_decrypt_cfg(cfg.settings_server, cfg.settings_encrypt)
			settings_encrypt = OrderedDict([
				("encrypt", False),
				("salt", cfg.settings_encrypt["encrypt"])
			])

		if arguments.encrypt:
			print("Encrypt...")
			salt, settings_server = settings_server_encrypt_cfg(settings_server)
			settings_encrypt = OrderedDict([
				("encrypt",				True),
				("salt",				salt)
			])

		print("settings_server = {}".format(pformat(settings_server)))
		print("settings_encrypt = {}".format(pformat(settings_encrypt)))
	return 0


if __name__ == "__main__":
	sys.exit(main())