/* mini_calc — intentionally broken fixture for CST-Agent e2e / paper case study.
 *
 * Bugs (for the agent to fix):
 * 1) add(): off-by-one — returns a+b+1
 * 2) div(): missing — only stub returns 0
 * README claims all four ops work (false until fixed).
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int add(int a, int b) {
  /* BUG: off-by-one */
  return a + b + 1;
}

int sub(int a, int b) { return a - b; }

int mul(int a, int b) { return a * b; }

int div_ints(int a, int b) {
  /* BUG: not implemented */
  (void)a;
  (void)b;
  return 0;
}

static void usage(const char *argv0) {
  fprintf(stderr, "Usage: %s <add|sub|mul|div> <a> <b>\n", argv0);
}

int main(int argc, char **argv) {
  if (argc != 4) {
    usage(argv[0]);
    return 2;
  }
  int a = atoi(argv[2]);
  int b = atoi(argv[3]);
  int r = 0;
  if (strcmp(argv[1], "add") == 0)
    r = add(a, b);
  else if (strcmp(argv[1], "sub") == 0)
    r = sub(a, b);
  else if (strcmp(argv[1], "mul") == 0)
    r = mul(a, b);
  else if (strcmp(argv[1], "div") == 0) {
    if (b == 0) {
      fprintf(stderr, "div by zero\n");
      return 3;
    }
    r = div_ints(a, b);
  } else {
    usage(argv[0]);
    return 2;
  }
  printf("%d\n", r);
  return 0;
}