#define BUF_SIZE 64
#define HEAP_SIZE 8192
static char heap[HEAP_SIZE];
static int  heap_top = 0;

void* kmalloc(int size) {
    void* ptr;
    if (heap_top + size > HEAP_SIZE) return 0;
    ptr = &heap[heap_top];
    heap_top += size;
    return ptr;
}
void print_char(char c);
char get_char(void);
int  check_key(void);
void set_cursor(void);
void set_cursor_pos(char row, char col);
int get_cursor_pos();
int str_eq(char* a, char* b) {
      int i = 0;
      while (a[i] && b[i]) {
          if (a[i] != b[i]) return 0;
          i++;
      }
      return a[i] == b[i];
  }
void print_string(char* str){
    int i = 0;
    while (str[i] != '\0'){
        print_char(str[i]);
        i++;
    }
}
void print_hex(unsigned int n) {
      char hex[] = "0x0000";
      int i;
      int nibble;
      for (i = 5; i >= 2; i--) {
          nibble = n & 0xF;
          hex[i] = nibble < 10 ? '0' + nibble : 'A' + nibble - 10;
          n >>= 4;
      }
      print_string(hex);
  }


 void read_line(char* buf) {
     int i = 0;
     char c;
     while (i < BUF_SIZE - 1) {
         c = get_char();
         if (c == '\r') break;        /* Enter */
         if (c == '\b' && i > 0) {   /* Backspace */
             i--;
             print_char('\b');
             print_char(' ');
             print_char('\b');
         } else {
             buf[i++] = c;
             print_char(c);           /* echo */
         }
     }
     buf[i] = '\0';
 }
 void kmain(void) {
      char buf[BUF_SIZE];
      set_cursor();
      print_string("senkOS> ");
      while (1) {
          read_line(buf);
          print_char('\n');
          if (str_eq(buf, "hello")) {
              print_string("world\n");
          } else {
              print_string("unknown command\n");
          }
          print_string("senkOS> ");
      }
  }