/* Build with: cc -Os -o nrj nrj.c */
#include <stdlib.h>
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <sys/select.h>
#ifndef NRJBITS
#define NRJBITS 16
#endif
#ifndef NRJWORD
#define NRJWORD unsigned short
#endif
#define NRJSIZE (1 << NRJBITS)
#define NRJWSIZE sizeof(NRJWORD)

int kbhit() {
  struct timeval tv = { 0L, 0L };
  fd_set fds;
  FD_ZERO(&fds);
  FD_SET(0, &fds);
  return select(1, &fds, NULL, NULL, &tv) > 0;
}

int getch() {
  int r;
  unsigned char c;
  if((r = read(0, &c, 1)) < 0) return r;
  else return c;
}

struct termios tty_opts_backup, tty_opts_raw;
void restore_term() {
  tcsetattr(STDIN_FILENO, TCSANOW, &tty_opts_backup);
}

void nrj_in(NRJWORD *ctxid, NRJWORD *val) {
  int x;
  if(*ctxid == (NRJWORD) 0) { /* for now, only emulate standard context id */
    *val = (NRJWORD) 0;
    if(kbhit()) {
      x = getch();
      if(x > -1)
        *val = (NRJWORD) x;
    }
  }
}

void nrj_out(NRJWORD *ctxid, NRJWORD *val) {
  if(*ctxid == (NRJWORD) 0) /* for now, only emulate standard context id */
    putchar((unsigned char) *val);
}

void nrj_load(NRJWORD* m, NRJWORD offset, char *fname) {
  FILE *prog = fopen(fname, "rb");
  if(prog) {
    fseek(prog, 0, SEEK_END);
    int flen = ftell(prog);
    fseek(prog, 0, SEEK_SET);
    fread(m+offset, NRJWSIZE, flen/NRJWSIZE, prog);
    fclose(prog);
    cfmakeraw(&tty_opts_raw);
    tcsetattr(STDIN_FILENO, TCSANOW, &tty_opts_raw);
  }
  else {
    printf("NRJ16: could not open the input file %s\r\n", fname);
    exit(1);
  }
}

void nrj_run(char *program) {
  NRJWORD maxaddr = (NRJWORD) (NRJSIZE - 1), mem[NRJSIZE], pc;
  mem[0] = mem[1] = mem[2] = (NRJWORD) 0;
  pc = (NRJWORD) 3;
  nrj_load(mem, pc, program);
  while(pc != maxaddr) {
    if(mem[0]) nrj_in(&mem[2], &mem[mem[0]]);
    mem[mem[pc]] = (~(mem[mem[pc]] | mem[mem[pc+1]])) & maxaddr;
    pc = mem[mem[pc+2]];
    mem[0] = (NRJWORD) 0;
    if(mem[1]) {
      nrj_out(&mem[2], &mem[mem[1]]);
      mem[1] = (NRJWORD) 0;
    }
  }
}

int main(int argc, char* argv[]) {
  tcgetattr(STDIN_FILENO, &tty_opts_backup);
  atexit(&restore_term);
  if(argc > 1)
    nrj_run(argv[1]);
  else {
    puts("NRJ16: no binary specified\r");
    return 1;
  }
  return 0;
}