/* X - Y ne k */

int fd_minus_ne_filter(fd_constraint this)
{
  fd_int x, y;
  int k;
  int value;

  x = VAR(this, 0);
  y = VAR(this, 1);
  k = this->constants[0];

  // only propagate if a variable domain is a singleton

  if (fd_var_single(x, &value) && _fd_var_del_val(value - k, y))
    {
      if (fd_domain_empty(y))
	return FD_NOSOLUTION;

      fd__constraint_set_entailed(this);

      _fd_revise_connected(this, y);
    }
  else if (fd_var_single(y, &value) && _fd_var_del_val(k + value, x))
    {
      if (fd_domain_empty(x))
	return FD_NOSOLUTION;

      fd__constraint_set_entailed(this);

      _fd_revise_connected(this, x);
    }

  return FD_OK;
}

int fd_minus_ne_propagate2(fd_constraint this, fd_int culprit)
{
  fd_int revise;
  int culprit_idx;
  int value;
  int changed = 0;

  // only propagate if culprit's domain is a singleton
  if (!fd_var_single(culprit, &value))
    return FD_OK;

  culprit_idx = culprit == VAR(this, 0) ? 0 : 1;
  revise = VAR(this, 1 - culprit_idx);

  if (culprit_idx == 0)
    changed = _fd_var_del_val(value - this->constants[0], revise);
  else
    changed = _fd_var_del_val(this->constants[0] + value, revise);

  if (changed)
    {
      if (fd_domain_empty(revise))
	return FD_NOSOLUTION;

      _fd_revise_connected(this, revise);
    }

  fd__constraint_set_entailed(this);

  return FD_OK;
}

int fd_minus_ne_propagate(fd_constraint this, fd_int revise)
{
  fd_int other;
  int other_idx;
  int value;
  int changed = 0;

  other_idx = revise == VAR(this, 0) ? 1 : 0;
  other = VAR(this, other_idx);

  // only propagate if other's domain is a singleton
  if (!fd_var_single(other, &value))
    return FD_OK;

  if (other_idx == 0)
    changed = _fd_var_del_val(value - this->constants[0], revise);
  else
    changed = _fd_var_del_val(this->constants[0] + value, revise);

  if (changed && fd_domain_empty(revise))
    return FD_NOSOLUTION;

  fd__constraint_set_entailed(this);

  // XXX: enqueue further updates here?
  if (changed)
    _fd_revise_connected(this, revise);

  return FD_OK;
}

fd_constraint fd_minus_ne(fd_int x, fd_int y, int k)
{
  fd_constraint c = _fd_constraint_new(2, 1);

  if (c)
    {
      c->variables[0] = FD_INT2C_VAR(x); c->variables[1] = FD_INT2C_VAR(y);
      c->constants[0] = k;
#ifdef CONSTRAINT_CLASS
      c->kind = FD_CONSTR_MINUS_NE;
#else /* CONSTRAINT_CLASS */
      c->propagator2 = fd_minus_ne_propagate2;
      c->propagator = fd_minus_ne_propagate;
#endif /* CONSTRAINT_CLASS */

      _fd_var_add_constraint(x, c);
      _fd_var_add_constraint(y, c);

      _fd_add_constraint(c);
    }

  return c;
}