#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>

#define USAGE "./mycp <file1> <file2>"
#define BUFF 1024

int main(int argc, char **argv) {
   if (argc != 3) {
      fprintf(stderr, "Illegal usage, must specify two files.\n"
         "Usage: %s\n", USAGE);
      exit(-1);
   }

   if (strcmp(argv[1], argv[2]) == 0) {
      fprintf(stderr, "%s and %s are identical.", argv[1], argv[2]);
      exit(-1);
   }

   int from = -1;
   int to = -1;

   while ((from = open(argv[1], O_RDONLY)) == -1 && errno == EINTR);
   if (from == -1) {
	   fprintf(stderr, "Couldn't open from file, %s.\n", argv[1]);
	   exit(-1);
   }
   while ((to = open(argv[2], O_WRONLY | O_CREAT)) == -1 && errno == EINTR);
   if (to == -1) {
      fprintf(stderr, "Couldn't open to file, %s.\n", argv[2]);
      close(from);
      exit(-1);
   }

   char buf[BUFF];
   ssize_t bytesRead = 0, bytesWritten = 0;

   while (1) {
      bytesRead = read(from, buf, BUFF);
      if (bytesRead == -1 && bytesRead != EINTR) {
         fprintf(stderr, "Error reading from file %s.", argv[1]);
         close(from);
         close(to);
         exit(-1);
      } else if (bytesRead == 0) {
         break;
      }

      while ((bytesWritten = write(to, buf, bytesRead)) == -1 && errno == EINTR);

   }

   close(from);
   close(to);
   exit(0);
}