/// <summary>
/// Evaluates a feature flag for a given user.
/// </summary>
/// <param name="flag">the flag; must not be null</param>
/// <param name="user">the user</param>
/// <param name="eventFactory">an <see cref="EventFactory"/> instance that will be called to produce any necessary
/// prerequisite flag events</param>
/// <returns>an <see cref="EvalResult"/> containing the evaluation result as well as any events that were produced;
/// the PrerequisiteEvents list will always be non-null</returns>
public EvalResult Evaluate(FeatureFlag flag, User user, EventFactory eventFactory)
{
if (flag.Key == FlagKeyToTriggerErrorForTesting)
{
throw new Exception(ErrorMessageForTesting);
}
if (user == null || user.Key == null)
{
_logger.Warn("User or user key is null when evaluating flag: {0} returning null",
flag.Key);
return(new EvalResult(
new EvaluationDetail <LdValue>(LdValue.Null, null, EvaluationReason.ErrorReason(EvaluationErrorKind.UserNotSpecified)),
ImmutableList.Create <EvaluationEvent>()));
}
var scope = new EvalScope(this, flag, user, eventFactory);
return(scope.Evaluate());
}
// Checks prerequisites if any; returns null if successful, or an EvaluationReason if we have to
// short-circuit due to a prerequisite failure. May add events to _prereqEvents.
private EvaluationReason?CheckPrerequisites()
{
foreach (var prereq in _flag.Prerequisites)
{
var prereqOk = true;
var prereqFeatureFlag = _parent._featureFlagGetter(prereq.Key);
if (prereqFeatureFlag == null)
{
_parent._logger.Error("Could not retrieve prerequisite flag \"{0}\" when evaluating \"{1}\"",
prereq.Key, _flag.Key);
prereqOk = false;
}
else
{
var prereqScope = new EvalScope(_parent, prereqFeatureFlag, _user, _eventFactory);
var prereqEvalResult = prereqScope.Evaluate();
var prereqDetails = prereqEvalResult.Result;
// Note that if the prerequisite flag is off, we don't consider it a match no matter
// what its off variation was. But we still need to evaluate it in order to generate
// an event.
if (!prereqFeatureFlag.On || prereqDetails.VariationIndex == null || prereqDetails.VariationIndex.Value != prereq.Variation)
{
prereqOk = false;
}
foreach (var subPrereqEvent in prereqEvalResult.PrerequisiteEvents)
{
_prereqEvents.Add(subPrereqEvent);
}
_prereqEvents.Add(_eventFactory.NewPrerequisiteEvaluationEvent(prereqFeatureFlag, _user,
prereqDetails, _flag));
}
if (!prereqOk)
{
return(EvaluationReason.PrerequisiteFailedReason(prereq.Key));
}
}
return(null);
}
