#include <stdio.h>
#include <stdlib.h>
#if (defined(WIN32) || defined(_WINDOWS)) && !defined(__CYGWIN__)
#define WIN
#define CLEAR() system("cls")
#include <windows.h>
#else
#define CLEAR() system("clear")
#include <termios.h> 
#include <sys/ioctl.h>
#include <unistd.h>
#endif
 
 
void Read_File(char *c, int max, FILE * ptr); //prototype
 
 
 
int getMaxX(void)
{
        #ifdef WIN
        CONSOLE_SCREEN_BUFFER_INFO csbi;
        if (GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi))
                return (int) csbi.dwSize.X;
        else
            return 0;
        #else
        struct winsize size;
        if (ioctl(STDIN_FILENO,TIOCGWINSZ, (char*) &size)<0) 
                return 0;
        else
                return size.ws_col;
        #endif
}
 
 
 
int main(int argc, char *argv[])
{
 
  int i, max;
  char * c;
  FILE *cfptr;
  cfptr = fopen(*(argv +1), "r");
  max = getMaxX();
  if(max == 0)
  {
  	printf("Error while tryong to determine the width of the window.\n");
  }	
  else if (cfptr == NULL)
  {
  	printf(" Error while opening the file\n");
  }
  else
  {
  	c = (char *) malloc(max*sizeof(char));
  	printf("File opened succesfully. Contents:\n\n");
  	Read_File(c, max, cfptr);
  }
 fclose(cfptr);
 
 return 0;
}
 
 
void Read_File(char *c, int max, FILE * ptr)
{
  int i;
  int a=0;
  char user;
  long int * size= (long int *) malloc(sizeof(long int));
  size[0] = 0;
  do
  {
            printf("\nPress N to continue. P to go backward\n");
            user = getchar();
            getchar();
 
            if((user == 'N') || (user == 'n'))
            {
 				CLEAR();
                for (i = 0; (i < 20 )&& fgets (c, max, ptr) != NULL; i++ )
                       printf("%s", c);
                fflush(stdout);
 				a++;
 				if((a+1)>sizeof(a)/sizeof(int))
 				size = (long int*) realloc(size, sizeof(long int)*(a+1));
                size[a]= ftell(ptr);

             }
            else if((user == 'P') || (user == 'p'))
            {
                 if (a > 1)
                 {
                 	 a -= 2;
                 	 CLEAR();
                     fseek(ptr, size[a], SEEK_SET);
                     for (i = 0; (i < 20) && fgets (c, max, ptr) != NULL; i++)
                     	printf("%s", c);
                     fflush(stdout);
                     a++;
                 }
              }
              else if((user == 'q') || (user == 'Q'))
              	exit(0);
    }while(!feof(ptr));
}