# -*- coding: utf-8 -*-
from struct import pack, unpack
from socket import socket, AF_INET, SOCK_DGRAM

from zk import const

class ZK(object):

    __data_recv = None

    def __init__(self, ip, port=4370, timeout=5):
        self.address = (ip, port)
        self.__address = (ip, port)
        self.__sock = socket(AF_INET, SOCK_DGRAM)
        self.__sock.settimeout(timeout)

    def __create_header(self, command, chksum=0, session_id=0, reply_id=65534,  command_string=''):
        '''
        Puts a the parts that make up a packet together and packs them into a byte string
        '''
        buf = pack('HHHH', command, chksum, session_id, reply_id) + command_string        
        buf = unpack('8B'+'%sB' % len(command_string), buf)
        chksum = unpack('H', self.__create_checksum(buf))[0]
        reply_id += 1
        if reply_id >= const.USHRT_MAX:
            reply_id -= const.USHRT_MAX

        buf = pack('HHHH', command, chksum, session_id, reply_id)
        return buf + command_string

    def __create_checksum(self, p):
        '''
        Calculates the chksum of the packet to be sent to the time clock
        Copied from zkemsdk.c
        '''
        l = len(p)
        chksum = 0
        while l > 1:
            chksum += unpack('H', pack('BB', p[0], p[1]))[0]
            p = p[2:]
            if chksum > const.USHRT_MAX:
                chksum -= const.USHRT_MAX
            l -= 2
        if l:
            chksum = chksum + p[-1]
            
        while chksum > const.USHRT_MAX:
            chksum -= const.USHRT_MAX
        
        chksum = ~chksum
        
        while chksum < 0:
            chksum += const.USHRT_MAX

        return pack('H', chksum)

    @property
    def __response(self):
        '''
        Checks a returned packet to see if it returned `CMD_ACK_OK` indicating success
        '''
        return unpack('HHHH', self.__data_recv[:8])[0]

    @property
    def __sesion_id(self):
        return unpack('HHHH', self.__data_recv[:8])[2]

    @property
    def __reply_id(self):
        return unpack('HHHH', self.__data_recv[:8])[3]

    def connect(self):
        '''
        connect to device
        '''

        command = const.CMD_CONNECT
        try:
            buf = self.__create_header(command=command)
            self.__sock.sendto(buf, self.address)
            self.__data_recv, addr = self.__sock.recvfrom(1024)

            if self.__response == const.CMD_ACK_OK:
                return (True, self.__response)
            else:
                return (False, self.__response)
        except Exception, e:
            return (False, e)

    def disconnect(self):
        '''
        diconnect from connected device
        '''

        command = const.CMD_EXIT
        try:
            buf = self.__create_header(command=command, session_id=self.__sesion_id, reply_id=self.__reply_id)
            self.__sock.sendto(buf, self.__address)
            self.__data_recv, addr = self.__sock.recvfrom(1024)
            if self.__response == const.CMD_ACK_OK:
                return (True, self.__response)
            else:
                return (False, self.__response)
        except Exception, e:
            return (False, e)