#!/usr/bin/env python3
import os, sys, logging, struct, psycopg2, bcrypt, random, atexit, time

# Database connection details. The credentials here need access to the Mastodon database, which "ejabberd" is unlikely
# to have on your system by default. You shoud grant SELECT privileges to ejabberd on the "accounts" and "users" tables,
# to play it safe, or include the Mastodon DB user credentials here (don't).
db_host="localhost"
db_port=5432
db_user="ejabberd"
db_pass=""
db_name="mastodon"

# This is the query that pulls the password hash for the given user. Mastodon doesn't store the domain for local accounts in
# the database, so we ignore the host component and try to match username where the domain is NULL.
db_query_getpass="select users.encrypted_password as password from accounts inner join users on accounts.id=users.account_id where accounts.username = %(user)s and accounts.domain is null"

########################################################################
#Setup
########################################################################

sys.stderr = open('/var/log/ejabberd/extauth_err.log', 'a')
logging.basicConfig(level=logging.INFO,
					format='%(asctime)s %(levelname)s %(message)s',
					filename='/var/log/ejabberd/extauth.log',
					filemode='a')

try:
	# Connect to the DB, set autocommit and readonly otherwise postgresql seems to have a 
	# tendency to keep things "idle in transaction" and table locks eventually grind
	# Mastodon to a halt. We don't make any changes anyway.
	database=psycopg2.connect(host = db_host, user = db_user, password = db_pass, database = db_name, port = db_port)
	database.set_session(readonly=True, autocommit=True)
	logging.debug(database.get_dsn_parameters())
except:
	logging.error("Unable to initialize database, check settings!")
	time.sleep(10)
	sys.exit(1)

@atexit.register
def close_db():
	cursor.close()
	database.close()

logging.info('auth-mastodon script started, waiting for ejabberd requests')

class EjabberdInputError(Exception):
	def __init__(self, value):
		self.value = value
	def __str__(self):
		return repr(self.value)


########################################################################
#Declarations
########################################################################

def ejabberd_in():
	logging.debug("trying to read 2 bytes from ejabberd:")

	input_length = sys.stdin.buffer.read(2)

	if len(input_length) is not 2:
		logging.debug("ejabberd sent us wrong things!")
		raise EjabberdInputError('Wrong input from ejabberd!')

	logging.debug('got 2 bytes via stdin: %s'%input_length)

	(size,) = struct.unpack('>h', input_length)
	logging.debug('size of data: %i'%size)

	income=sys.stdin.read(size)
	logging.debug("incoming data: %s"%income)

	return income


def ejabberd_out(bool):
	logging.debug("Ejabberd gets: %s" % bool)

	token = genanswer(bool)

	logging.debug("sent bytes: %#x %#x %#x %#x" % (token[0], token[1], token[2], token[3]))

	sys.stdout.buffer.write(token)
	sys.stdout.buffer.flush()


def genanswer(bool):
	answer = 0
	if bool:
		answer = 1
	token = struct.pack('>hh', 2, answer)
	return token


def get_password(user, host):
	# Right now we ignore the host component, as Mastodon doesn't store it for local accounts.
	# It may be required one day, so the code to handle passing it to the query is left in for now.
	cursor = database.cursor()
	cursor.execute(db_query_getpass, {"user": user, "host": host})
	data = cursor.fetchone()
	cursor.close()
	return data[0] if data != None else None


def isuser(user, host):
	return get_password(user, host) != None


def auth(user, host, password):
	db_password = get_password(user, host)
	if db_password == None:
		logging.debug("Wrong username: %s@%s" % (user, host))
		return False
	else:
		if bcrypt.checkpw(password.encode('utf8'), db_password.encode('utf8')):
			logging.debug("Validated %s against hash %s" % (user, db_password))
			return True
		else:
			logging.debug("Wrong password for user: %s@%s" % (user, host))
			return False


########################################################################
#Main Loop
########################################################################

exitcode=0

while True:
	logging.debug("start of infinite loop")

	try:
		ejab_request = ejabberd_in().split(':', 3)
	except EOFError:
		break
	except Exception as e:
		logging.exception("Exception occured while reading stdin")
		raise

	op_result = False
	try:
		# Only 'auth' and 'isuser' implemented, placeholders left to maybe 
		# expose other functions later but for now let's not even think about 
		# modifying the Mastodon DB
		if ejab_request[0] == "auth":
			op_result = auth(ejab_request[1], ejab_request[2], ejab_request[3])
		elif ejab_request[0] == "isuser":
			op_result = isuser(ejab_request[1], ejab_request[2])
		elif ejab_request[0] == "setpass":
			op_result = False
		elif ejab_request[0] == "tryregister":
			op_result = False
		elif ejab_request[0] == "removeuser":
			op_result = False
		elif ejab_request[0] == "removeuser3":
			op_result = False
	except Exception:
		logging.exception("Exception occured")

	ejabberd_out(op_result)
	logging.info("successful" if op_result else "unsuccessful")

logging.debug("end of infinite loop")
logging.info('extauth script terminating')
database.close()
sys.exit(exitcode)