/*
* Copyright (c) 2008, mibo@student.math.hr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*     * Redistributions of source code must retain the above copyright
*       notice, this list of conditions and the following disclaimer.
*
* THIS SOFTWARE IS PROVIDED BY mibo@student.math.hr ''AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL mibo@student.math.hr BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*
Compile:
gcc -o privitak privitak.c
*/

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <string.h>

#define M 256
#define SWAP(A, B)(A ^= B ^= A ^= B)

unsigned char S[M], K[M];

void inicijaliziraj(unsigned char k[], short n){
  register short i, j;

  for(i = 0; i < M; i++)
    S[i] = (unsigned char)i;
  for(i = 0; i < M; i++)
    K[i] = k[i % n];
  for(i = 0, j = 0; i < M; i++){
    j = (j + S[i] + K[i]) % M;
    SWAP(S[i], S[j]);
  }
}

unsigned char daj(void){
  static short i = 0, j = 0;

  i = (i + 1)    % M;
  j = (j + S[i]) % M;
  SWAP(S[i], S[j]);

  return S[((S[i] + S[j]) % M)];
}

void iznimka(char *s){
   printf("Iznimka: %s\n:-(\n", s);
   scanf("%%");
   exit(-1);
}

void zaboravi(void){
   short i;
   for(i = 0; i < M; i++)
      S[i] = K[i] = 0;
}

void poziv(void){
   printf("Poziv programa: \n");
   printf("'privitak p program.exe attachment.txt' za pakiranje datoteke program.exe u datoteku attachment.txt");
   printf("\nili\n");
   printf("'privitak r attachment.txt program.exe' za raspakiravanje datoteke attachment.txt u datoteku program.exe");
   printf("\n");
   exit(0);
}

int main(int argc, char *argv[]){
   unsigned char k[M] = {0};
   FILE *u, *i;
   int j;
   unsigned int z;
   
   srand(time(NULL));
   
   if(argc != 4)
      poziv();
   
   if(strcmp(argv[1], "p") != 0 && strcmp(argv[1], "r") != 0) iznimka("Ne prepoznajem prvi parametar.");
   
   if(strcmp(argv[1], "p") == 0){
      if((u = fopen(argv[2], "rb")) == NULL) iznimka("Ne mogu otvoriti datoteku.");
      if((i = fopen(argv[3], "wt")) == NULL) iznimka("Ne mogu otvoriti datoteku za pisanje.");
      
      for(j = 0; j < M; j++)
         fprintf(i, "%.2X ", k[j] = rand() % M);
      
      inicijaliziraj(k, M);
      
      for(j = 0; j < 2008; j++)
         daj(); /* :-) */
         
      while(!feof(u)){
         if((z = fgetc(u)) == EOF) break;
         fprintf(i, "%.2X ", ((unsigned char)z) ^ daj());
      }
         
      fclose(u); fclose(i);
   }
   else{    
      if((u = fopen(argv[2], "rt")) == NULL) iznimka("Ne mogu otvoriti datoteku.");
      if((i = fopen(argv[3], "wb")) == NULL) iznimka("Ne mogu otvoriti datoteku za pisanje.");
      
      for(j = 0; j < M; j++){
         if(fscanf(u, "%X ", &z) != 1)
         k[j] = (unsigned char)z;
      }

      inicijaliziraj(k, M);
      
      for(j = 0; j < 2008; j++)
         daj(); /* :-) */
         
      while(!feof(u)){
         if(fscanf(u, "%X ", &z) != 1)
            break;
         fputc((unsigned char)z ^ daj(), i);
      }
      
      fclose(u); fclose(i);
   }
   
   zaboravi();
   
   return 0;
}