import socket
from time import sleep
import struct
import json
import shelve


def pack_data(data):
    encoded = data.encode()
    return struct.pack('I', len(encoded)) + encoded


def prepare_data(data):
    cmd, args = data.split(' ', maxsplit=1)

    if cmd == 'get':
        return json.dumps({'method': 'get', 'path': args})

    elif cmd == 'cp':
        paths = args.split()
        if len(paths) != 2:
            raise ValueError('Неверное количество путей в параметрах.')
        src, dest = args.split()
        if src not in db:
            return json.dumps({'method': 'get_cp', 'path': src})
        with open(dest, 'wb') as f:
            f.write(db[src])

    else:
        raise ValueError('Команда не распознана')


def parse_response(data):
    return json.loads(data.decode())


def get_response(connection):
    buffer = b''
    while len(buffer) < DATATYPE_SIZE:
        data = connection.recv(DATATYPE_SIZE - len(buffer))
        if not data:
            raise ConnectionError('Connection was closed')

        buffer += data

    size_packed, buffer = buffer[:DATATYPE_SIZE], buffer[DATATYPE_SIZE:]
    if not size_packed:
        raise ConnectionError('Connection was closed')

    (size,) = struct.unpack('I', size_packed)
    data = connection.recv(size - len(buffer))
    return parse_response(buffer + data)


def download_file(filesize, connection):
    data = b''
    count = 0
    while count < filesize:
        (size,) = struct.unpack('I', connection.recv(DATATYPE_SIZE))
        data += connection.recv(size)
        count += size

    return data


def handle_response(data, connection):
    if data['status'] == 0:
        print(f'Загружаем файл размером {data["size"]} байт...')
        file_data = download_file(data['size'], connection)
        db[data['path']] = file_data
        print('Загрузка завершена')

    elif data['status'] == 1:
        print(data['reason'])

    elif data['status'] == 2:
        print('Неизвестная ошибка:')
        print(data['reason'])


def try_connect():
    cnt = 0
    sock = socket.socket()
    while cnt < 10:
        try:
            cnt += 1
            sock.connect(ADDR)

        except ConnectionRefusedError:
            print('Не удалось подключиться к серверу. Следующая попытка через 3 секунды...')
            sleep(3)

        else:
            return sock

    else:
        print('Не удалось подключиться к серверу через 10 попыток.\nОстанавливаемся...')
        sock.close()
        return


HOST, PORT = ADDR = 'localhost', 6000
DATATYPE_SIZE = 4  # int

sock = try_connect()
if sock is None:
    quit()


db = shelve.open('backdoor.db')

while True:
    try:
        data = input('Введите команду:\n')
        data = prepare_data(data)
        if data is None:
            continue

    except KeyboardInterrupt:
        break

    except ValueError as err:
        print(err)

    else:
        packet = pack_data(data)
        sock.sendall(packet)
        response = get_response(sock)
        handle_response(response, sock)

sock.close()