#include <string.h>

/* binary constraint (between X and Y) defined through the disallowed pairs */

int fd_nogoods_propagate(fd_constraint this, fd_int revise)
{
  fd_int other;
  int rx, ox;	// variables' indexes within the constraint
  int value;
  int changed = 0;
  int i;

  rx = revise == VAR(this, 0) ? 0 : 1;
  ox = 1 - rx;

  other = VAR(this, ox);

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

  for (i = 0; i < this->nconstants; i += 2)
    if (this->constants[i + ox] == value)
      changed |= _fd_var_del_val(this->constants[i + rx], revise);

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

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

  return FD_OK;
}

fd_constraint fd_nogoods(fd_int x, fd_int y, int *nogoods, int nnogoods)
{

  fd_constraint c = _fd_constraint_new(2, 2 * nnogoods);

  if (c)
    {
      c->variables[0] = FD_INT2C_VAR(x); c->variables[1] = FD_INT2C_VAR(y);

#ifdef CONSTRAINT_CLASS

      c->kind = FD_CONSTR_NOGOODS;

#else /* CONSTRAINT_CLASS */
      c->propagator = fd_nogoods_propagate;
#endif /* CONSTRAINT_CLASS */

      memcpy(c->constants, nogoods, 2 * nnogoods * sizeof(int));

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

      _fd_add_constraint(c);
    }