#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <fstream>
#include <cctype>
#include <cstring>
#include <sstream>
#include <string>
using namespace std;
string polynomial, seed, message;
int size = 0;

void printArray(short *arr){
    for(int i = 0; i < size; i++){
        cout<<arr[i];
    }
    cout<<endl;
}
void shiftArray(short *arr, int amount){
    if(amount > 0){
        for(int i = size - 1; i >= amount; i--){
            arr[i] = arr [i - amount];
        }
        for(int i = amount - 1; i >= 0; i--){
            arr[i] = 0;
        }
    }
    else if (amount < 0){
        for(int i = 0; i < size + amount; i++){
            arr[i] = arr[i - amount];
        }
        for(int i = size + amount; i < size; i++){
            arr[i] = 0;
        }
    }
}

short generateBit(short *arr){
    short bit = 0;
    for(int i = 0; i < size; i++){
        if(polynomial[i] == '1'){
            bit += arr[i];
        }
    }
    return bit % 2;
}

bool compareArrays(short *arr1, short*arr2){
    for(int i = 0; i < size; i++){
        if(arr1[i] != arr2[i])
            return false;
    }
    return true;
}
string encryptMessage(string basicString){
    polynomial = polynomial.substr(1,polynomial.length());
    size = polynomial.length();
    short *lfsr = new short [size];
    string outString="";
    for(int i = 0; i<size; i++){
        lfsr[i] = seed[i];
    }
  for(int i = 0; i < basicString.length();i++){
    short temp = generateBit(lfsr);
    short out = temp^basicString[i];
    outString+=out;
    shiftArray(lfsr, 1);
    lfsr[0] = out;
   }
   return outString;
}
string decryptMessage(string basicString){
    polynomial = polynomial.substr(1,polynomial.length());
    size = polynomial.length();
    short *lfsr = new short [size];
    string outString="";
     for(int i = 0; i<size; i++){
        lfsr[i] = seed[i];
    }
    for(int i = 0; i < basicString.length();i++){
    short temp = generateBit(lfsr);
    short out = temp^basicString[i];
    outString+=out;
    shiftArray(lfsr, 1);
    lfsr[0] = basicString[i];
   }
   return outString;
}

int main(int argc, char **argv){
    string inName;
    string outName;
    char c;
    int o;
    bool encrypt = false;
    bool decrypt = false;
    bool polynomialEntered = false;
    bool seedEntered = false;
    char* arr1;
        while ((o = getopt (argc, argv, "edp:s:i:o:")) != -1) {
        switch (o) {
            case 'e':
                encrypt = true;
                break;
            case 'd':
                decrypt = true;
                break;
            case 'p':
                polynomialEntered = true;
                arr1 = optarg;
                polynomial = string(arr1);
                break;
            case 's':
                seedEntered = true;
                arr1 = optarg;
                seed = string(arr1);
                break;
            case 'i':
                arr1 = optarg;
                inName = string(arr1);
                break;
            case 'o':
                arr1 = optarg;
                outName = string(arr1);
                break;
        }
    }
    ifstream input (inName, ios::binary);
    ofstream output (outName);
    ostringstream ss;
    ss << input.rdbuf();
    string dataFromFile = ss.str();
    if(!input || ! output){
        printf("Unable to open input or output file! \n");
        printf("Input file should be given using flag -i and output -o ");
        return 0;
    }

    if(!encrypt && !decrypt){
        printf("Use flag -e to encrypt and -d to decrypt\n");
        return 0;
    }
    if(!polynomialEntered || !seedEntered){
        printf("Please specify polynomial and seed.");
        cout<<polynomial<<" "<<seed;
        return 0;
    }
    if(polynomial.size()-1 != seed.size()){
        printf("Polynomial size and seed size must be equal.");
        return 0;
    }


  if(encrypt){
      output<<encryptMessage(dataFromFile);
    }
    if(decrypt){
      output<<decryptMessage(dataFromFile);
    }
}