#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import argparse
import socket
import datetime
import random
import time
import crcmod.predefined


IDENT_NR = 0


def crc16_modbus(data: bytes) -> int:
    crc = crcmod.predefined.Crc('modbus')
    crc.update(data)
    return int(crc.hexdigest(), 16)


def handle_systec_it3000a(req: bytes) -> bytes:
    global IDENT_NR

    if not req.startswith(b'<') or not req.endswith(b'>'):
        return b'<31>\r\n'
    req = req[1:-1]

    if req in (b'OS01', b'OS02', b'OC01', b'OC02'):
        # set or clear outputs 1 or 2
        return b'<00>\r\n'
    elif len(req) > 3:
        return b'<32>\r\n'
    if req.startswith(b'RN'):
        incr = True
    elif req.startswith(b'RM'):
        incr = False
    else:
        return b'<32>\r\n'

    if incr:
        time.sleep(random.randint(0, 40) / 10.0)

    gew = random.randint(40, 4000)
    m = random.randint(1, 10)
    match m:
        case 1:
            return b'<12>\r\n'
        case 2:
            incr = False
            gew = 0

    if incr:
        IDENT_NR += 1
    now = datetime.datetime.now()
    data = f'0000{now:%d.%m.%y%H:%M}{IDENT_NR if incr else 0:4}1{gew:8}{0:8}{gew:8}kg   {1:3}'.encode('ascii')
    return b'<' + data + f'{crc16_modbus(data):8}'.encode('ascii') + b'>\r\n'


def log(msg: bytes) -> None:
    print(msg.decode('ascii'), end='', flush=True)


def main() -> None:
    s = socket.socket()
    s.bind(('0.0.0.0', 1234))
    s.listen()
    print('Ready for connections')

    while True:
        c, (addr, port) = s.accept()
        print(f'Accepting connection from [{addr}]:{port}')
        try:
            while True:
                req = c.recv(1024)
                log(req)
                res = handle_systec_it3000a(req)
                log(res)
                c.send(res)
        except:
            pass


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    args = parser.parse_args()
    main()