#include <fcntl.h>
#include <stdio.h>
#define MULTI 3
#define BITOUT "bitout.txt"
#define ASCIIOUT "asciiout.txt"

void encode(int fd, char codes[]);
void decode(int fd, char codes[]);

int main(int argc, char **argv)
{
  int fd;
  char *filename;
  char codes[] = "abcdefghij";


  if(argc < 3)
    {
      printf("wrong\n");
      exit(-1);
    }
  
  fd = open(argv[2], O_RDONLY, 0); 
  
  if(fd > 0)
    {
      printf("file opened\n");
    }
  else 
    {
      printf("invalid filename\n");
      exit(-1);
    }
  
  if(strcmp(argv[1], "encode") == 0)
    {
      encode(fd, codes);
    }
  else if(strcmp(argv[1], "decode") == 0)
    {
      decode(fd, codes);
    }
  else
    {
      printf("wrong\n");
    }
}




void encode(int fd, char codes[])
{
  int fdout;
  char letter;
  char prevletter;
  int test;
  int code;
  unsigned int similar=1;
  unsigned char writebyte= '\0';
  int bitindex = 6;
  int count=0;

  fdout = creat(BITOUT, 0600);
  
  fdout = open(BITOUT, O_WRONLY, 0); 
  
  printf("encode\n");
  
  test = read(fd, &prevletter, 1);
  
  while(test != 0)
    {
      test = read(fd, &letter, 1);
      
      if(letter == prevletter)
	{
	  similar++;
	}
      else
	{
	  if(similar > 1)
	    {
	      writebyte |= (MULTI << (bitindex));
	      bitindex -=2;
	      if(bitindex < 0)
		{
		  bitindex = 6;
		  write(fdout, &writebyte, 1);
		  writebyte = '\0';
		}
	      
	      if(bitindex > 0)
		{
		  writebyte |= (similar << (bitindex-2));
		  bitindex -=4;
		}
	      else 
		{
		  writebyte |= similar >> 2;
		  write(fdout, &writebyte, 1);
		  writebyte = '\0';
		  bitindex = 6;
		  writebyte |= code << (bitindex);
		  
		}


	      if(bitindex < 0)
		{
		bitindex = 6;
		write(fdout, &writebyte, 1);
		writebyte = '\0';
		}
	      similar = 1;
	    }
	  
	    
	  count = 0;
	  code = 0;
	  while(count < 11 && code == 0)
	    {
	      if(codes[count] == prevletter)
		code = count+1;
	      
	      count++;
	    }
	  
	  if(bitindex > 0)
	    {
	      writebyte |= code << (bitindex-2);
	      bitindex -=4;
	    }
	  else 
	    {
	      writebyte |= code >> 2;
	      write(fdout, &writebyte, 1);
	      writebyte = '\0';
	      bitindex = 6;
	      writebyte |= code << (bitindex);
	      bitindex -=2;
	    }
	  
	  if(bitindex < 0)
	    {
	      bitindex = 6;
	      write(fdout, &writebyte, 1);
	      writebyte = '\0';
	    }
	}
	
      prevletter = letter;
    }
  if(bitindex != 6)
    {
      writebyte |= 0;
      write(fdout, &writebyte, 1);
    }
  close(fdout);
  
}

void decode(int fd, char codes[])
{
  int fdout;
  unsigned char byte='\0';
  unsigned char prevbyte='\0';
  unsigned char temp;
  int test;
  int code;
  unsigned int similar=1;
  char writechar= '\0';
  int bitindex = 6;
  int i;
  
  fdout = creat(ASCIIOUT, 0600);
  fdout = open(ASCIIOUT, O_WRONLY, 0); 
  
  test = read(fd, &prevbyte, 1);
  test = read(fd, &byte, 1);

  while(test != 0)
    {
      if( ((prevbyte  >> bitindex)& MULTI )==  MULTI)
	{
	  bitindex -= 2;
	  if(bitindex < 0)
	    {
	      bitindex = 6;
	      prevbyte = byte;
	      test = read(fd, &byte, 1);
	    }
	  	  
	  if(bitindex < 2)
	    {
	      similar = ((prevbyte & 3) << 2) | (byte >> 6);
	    }
	  else
	    { 
	      temp = prevbyte << (6-bitindex);
	      similar = temp >> (4);
	    }
	  
	  bitindex += 8;
	  bitindex -= 4;
	  bitindex %= 8;
	  if(bitindex > 2)
	    {
	      prevbyte = byte;
	      test = read(fd, &byte, 1);
	    }

	}
      
      
      if(bitindex < 2)
	{
       	  
	code = ((prevbyte & 3) << 2) | (byte >> 6);
	}
      else 
	{
	  temp = prevbyte << (6 - bitindex);
	  code = temp >> (4);
      
	}
      bitindex += 8;
      bitindex -= 4;
      bitindex %= 8;
      if(bitindex > 2)
	{
	  prevbyte = byte;
	  test = read(fd, &byte, 1);
	}
      
      for(i=0; i<similar; i++)
	{
	  write(fdout, &codes[code-1], 1);
	}
    }
  close(fdout);
}