from math import factorial as fact
from random import random

class Packet(object):

    def __init__(self, nDataBits, nOverheadBits, nRedundantBits):
        self.u = nDataBits
        self.o = nOverheadBits
        self.k = nDataBits + nOverheadBits
        self.n = nDataBits + nOverheadBits + nRedundantBits
        self.computeHammingBound()

    def send(self, bitErrorRate):
        '''
        Repeatedly attempts to send the packet until successful while simulating
        the specified bit error rate. Returns the efficiency of the packet.
        '''
        attempts = 0
        sent = False
        while not sent:
            attempts += 1
            errors = 0
            for i in xrange(self.n):
                if random() < bitErrorRate:
                    errors += 1
            sent = (errors <= self.t)
        return float(self.u)/(self.n*attempts)

    def computeHammingBound(self):
        limit = 2**(self.n-self.k)
        total = 0
        t = 0
        while total <= limit:
            print total,limit
            total += fact(self.n) / (fact(t)*fact(self.n-t))
            t += 1
        self.t = t-2

    def __repr__(self):
        return ("=PACKET=======\n"+
                 "Data bits: %d\n"%self.u+
                 "Overhead bits: %d\n"%self.o+
                 "Redundant bits: %d\n"%(self.n-self.k)+
                 "Hamming bound: %d\n"%self.t+
                 "==============")


if __name__ == '__main__':
    while True:
        nDataBits = input("Input user data size: ")
        nRedundantBits = input("Input redundant bits: ")
        bitErrorRate = input("Input bit error rate: ")
        packet = Packet(nDataBits, 100, nRedundantBits)
        print "Packet ready:"
        print packet
        raw_input("Press enter to simulate 1,000,000 transmissions with bit "+
                  "error rate of %f"%bitErrorRate)
        efficiency = 0.0
        N = 1000000
        for i in xrange(100):
            for _ in xrange(N/100):
                efficiency += packet.send(bitErrorRate)
            print "%d%% complete..."%i
        efficiency /= N
        print "1,000,000 packets transferred with %2.3f efficiency"%efficiency
        if raw_input("Again? y/n: ").lower() in ("n","no","x","q"):
            exit()