#include <alloca.h>
#include <assert.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <ffi.h>

void rt_3addiii(int *res, int a, int b)
{
    *res = a + b;
}

void rt_3subiii(int *res, int a, int b)
{
    *res = a - b;
}

void rt_2eqbii(bool *res, int a, int b)
{
    *res = a == b;
}

void rt_2if(bool test, ...)
{
  va_list args;
  va_start(args, test);

  if (!test)
  {
    int num_skip = va_arg(args, int);

    for (int i = 0; i < num_skip; i++)
    {
      (void) va_arg(args, ffi_type*);
      (void) va_arg(args, void*);
    }
    va_arg(args, void(*)());
  }

  int num_args = va_arg(args, int);

  ffi_cif cif;
  ffi_arg ret;
  ffi_type **types = alloca(sizeof(ffi_type*) * num_args);
  void **values = alloca(sizeof(void(*)()) * num_args);

  for (int i = 0; i < num_args; i++)
  {
    types[i] = va_arg(args, ffi_type*);
    values[i] = va_arg(args, void*);
  }
  void (*fun)() = va_arg(args, void*);

  ffi_status result = ffi_prep_cif(&cif, FFI_DEFAULT_ABI, num_args, &ffi_type_void, types);
  assert(result == FFI_OK);
  ffi_call(&cif, fun, &ret, values);
}

int zero = 0;
int one = 1;

void ack(int *res, int m, int n);

void ack_ret2(int *res, int m)
{
  int temp;
  rt_3subiii(&temp, m, one);
  ack(res, temp, one);
}

void ack_rest2(int *res, int m, int n)
{
  int temp1, temp2, temp3;
  rt_3subiii(&temp1, n, one);
  ack(&temp2, m, temp1);
  rt_3subiii(&temp3, m, one);
  ack(res, temp3, temp2);
}

void ack_ret1(int *res, int n)
{
  rt_3addiii(res, n, one);
}

void ack_rest1(int *res, int m, int n)
{
  bool temp;
  rt_2eqbii(&temp, n, zero);
  rt_2if(temp,
         2, &ffi_type_pointer, &res, &ffi_type_sint32, &m, &ack_ret2,
         3, &ffi_type_pointer, &res, &ffi_type_sint32, &m, &ffi_type_sint32, &n, &ack_rest2
  );
}

void ack(int *res, int m, int n)
{
  bool temp;
  rt_2eqbii(&temp, m, zero);
  rt_2if(temp,
         2, &ffi_type_pointer, &res, &ffi_type_sint32, &n, &ack_ret1,
         3, &ffi_type_pointer, &res, &ffi_type_sint32, &m, &ffi_type_sint32, &n, &ack_rest1
  );
}

int wrap_ack(int m, int n)
{
  int res;
  ack(&res, m, n);
  return res;
}

int main(int argc, const char *argv[])
{
  for (int i = 0; i < 10; ++i)
  {
    printf("ack(3, 7) = %i\n", wrap_ack(3, 7));
  }
}