import TLVutils
from time import time
from random import seed, randint
from ConstantDefinitions import *
from utils import inttostring, stringtoint

class ControlReferenceTemplate:
    def __init__(self,type,config=""):
        """
        Generates a new CRT
        @param type: Type of the CRT (HT, AT, KT, CCT, DST, CT-sym, CT-asym) 
        @param config: A string containing TLV encoded Security Environment parameters 
        """
        if type not in (TEMPLATE_AT, TEMPLATE_HT, TEMPLATE_KAT, TEMPLATE_CCT, TEMPLATE_DST, TEMPLATE_CT):
            raise ValueError, "Unknown control reference tag."
        else:
            self.type = type

        self.iv = None
        self.keyref = None
        self.key = None
        self.fileref = None
        self.DFref = None
        self.keylength = None
        self.algorithm = None
        self.usage_qualifier = None
        if config != "":
            self.parse_SE_config(config)
	    self.__config_string = config
        
    def parse_SE_config(self,config):
        structure = TLVutils.unpack(config)
        for object in structure:
            tag, length, value = object    
            if tag == 0x80:
                self.__set_algo(data)
            elif tag in (0x81,0x82,0x83,0x84):
                self.__set_key(tag,length,value)
            elif tag in range(0x85, 0x93):
                self.__set_iv(tag,length,value)
            elif tag == 0x95:
                self.usage_qualifier = data
            
    def __set_algo(self,data):
        if not ALGO_MAPPING.has_key(data):
            raise ValueError
        else:
            #TODO: Sanity checking
            self.algorithm = ALGO_MAPPING[data]
            self.__replace_tag(0x80,data)
    
    def __set_key(self,tag,length,value):
        if tag == 0x81:
            self.fileref = value
        elif tag == 0x82:
            self.DFref = value
        elif tag in (0x83,0x84):
            #Todo: Resolve reference
            self.keyref = value
    
    def __set_iv(self,tag,length,value):
        iv = None
        if tag == 0x85:
            iv = 0x00
        elif tag == 0x86:
            pass #What is initial chaining block?
        elif tag == 0x87 or tag == 0x93:
            if length != 0:
                iv = value
            else:
                iv = self.iv + 1
        elif tag == 0x91:
            if length != 0:
                iv = value
            else:
                seed(time())
                iv = hex(randint(0,255))
        elif tag == 0x92:
            if length != 0:
                iv = value
            else:
                iv = int(time())
        self.iv = iv
       
    def __replace_tag(self,tag,data):
        position = 0
        while self.__config_string[position:position+1] != tag and position < len(self.__config_string):    
            length = inttostring(self.__config_string[position+1:position+2])
            position += length + 3 
        if position < len(self.__config_string): #Replace Tag
            length = inttostring(self.__config_string[position+1:position+2])
            self.__config_string = self.__config_string[:position] + tag + inttostring(len(data)) + data + self.__config_string[position+2+length:]
        else: #Add new tag
            self.__config_string += tag + inttostring(len(data)) + data
    
    def to_string(self):
        """
        Return the content of the CRT, encoded as TLV data in a string
        """
        return self.__config_string
    
    def __str__(self):
        return self.__config_string