/// <summary>
/// Applies the operator backwards to the given target relative state. The result is a new relative state (or more relative states, if conditional effects are present).
/// </summary>
/// <param name="relativeState">Relative state for the application.</param>
/// <param name="operatorPreconditions">Operator preconditions.</param>
/// <returns>Preceding relative states.</returns>
public IEnumerable <IRelativeState> ApplyBackwards(IRelativeState relativeState, ISimpleConditions operatorPreconditions)
{
IRelativeState result = (IRelativeState)relativeState.Clone();
bool anyConditionalEffect = false;
foreach (var effect in this)
{
if (effect.GetConditions() == null)
{
result = effect.ApplyBackwards(result);
}
else
{
anyConditionalEffect = true;
}
}
foreach (var constraint in operatorPreconditions)
{
result.SetValue(constraint.GetVariable(), constraint.GetValue());
}
if (!anyConditionalEffect)
{
yield return(result);
}
else
{
List <IRelativeState> states = new List <IRelativeState> {
result
};
foreach (var effect in this)
{
if (effect.GetConditions() != null)
{
int statesCount = states.Count;
for (int i = 0; i < statesCount; ++i)
{
var newEffect = effect.ApplyBackwards(states[i]);
if (newEffect != null)
{
states.Add(newEffect);
}
}
}
}
foreach (var state in states)
{
yield return(state);
}
}
}
/// <summary>
/// Applies the effect backwards to the given relative state.
/// </summary>
/// <param name="relativeState">Relative state.</param>
public virtual IRelativeState ApplyBackwards(IRelativeState relativeState)
{
// we are fine here with the direct modification
relativeState.SetValue(Assignment.GetVariable(), RelativeState.WildCardValue);
return(relativeState);
}