protected override IEnumerable <ParseStep> ParseSpecific(IRegexEngine engine, State initialState, StringBuilder matchedText)
{
// At this point, we know we'll match. Attempt to match everything else, until we hit max, a non-match, or the end of the string.
// We need to save states as we go, in case we're asked to backtrack.
var savedStates = new Stack <SavedState>();
int matchedQuantity = Min;
for (; Max == null || matchedQuantity < Max; matchedQuantity++)
{
// If the last state we saved was at the end of the string, there's no point in going any further...
if (savedStates.Count > 0 && savedStates.Peek().State.Index >= engine.Input.Length)
{
// Should we ever get here???
savedStates.Pop();
break;
}
if (engine.State.Index < engine.Input.Length)
{
// We're not at the end of the string, so save state before attempting a match - since we're greedy, we leave breadcrumbs before doing anything.
savedStates.Push(new SavedState(engine.State, matchedText.ToString()));
yield return(ParseStep.StateSaved(this, engine.State, string.Format("Saving state - index {0}", engine.State.Index)));
}
else
{
// It looks like we're at the end of the string - which means we're done. Time to report as such.
yield return(ParseStep.EndOfString(this, engine.State));
yield return(ParseStep.Pass(this, matchedText.ToString(), initialState, engine.State));
yield return(ParseStep.Break(this));
break;
}
var endOfMatch = false;
// TODO: I think that we're going to need to use an enumerator here so we can initiate backtracking in our child and its descendants.
foreach (var result in Child.Parse(engine))
{
if (result.Type == ParseStepType.Break && ReferenceEquals(Child, result.Node))
{
break;
}
yield return(result);
if (ReferenceEquals(Child, result.Node))
{
if (result.Type == ParseStepType.Pass)
{
matchedText.Append(result.MatchedText);
}
else if (result.Type == ParseStepType.Fail)
{
endOfMatch = true;
foreach (var backtrackStep in Backtrack(engine, initialState, savedStates))
{
yield return(backtrackStep);
}
break;
}
}
}
if (endOfMatch)
{
break;
}
}
if (matchedQuantity >= Max)
{
// We've reached the maximum allowed quantity of repetitions, time to break;
yield return(ParseStep.Pass(this, matchedText.ToString(), initialState, engine.State));
yield return(ParseStep.Break(this));
}
// If we get here, it means that we're backtracking
while (savedStates.Count > 0)
{
foreach (var backtrackStep in Backtrack(engine, initialState, savedStates))
{
yield return(backtrackStep);
}
}
// If we get here, we ran out of saved states to backtrack to - report failure.
yield return(ParseStep.Fail(this, initialState, engine.State, "No backtrack is available"));
if (engine.State.Index != initialState.Index)
{
yield return(ParseStep.ResetIndex(this, initialState, engine.State));
engine.State = initialState;
}
yield return(ParseStep.Break(this));
}
internal override IEnumerable <ParseStep> Parse(IRegexEngine engine)
{
yield return(ParseStep.BeginParse(this, engine.State));
var initialState = engine.State;
var choiceIndex = 0;
foreach (var choice in Choices)
{
var matchedText = "";
var choicePassed = false;
foreach (var result in choice.Parse(engine))
{
if (ReferenceEquals(choice, result.Node) && result.Type == ParseStepType.Break)
{
break;
}
yield return(result);
if (ReferenceEquals(choice, result.Node))
{
if (result.Type == ParseStepType.Pass)
{
matchedText = result.MatchedText;
choicePassed = true;
if (choiceIndex < Choices.Count - 1)
{
// Only save state if we're not the last choice...
yield return(ParseStep.StateSaved(this, initialState, string.Format("Saving state - index {0}", engine.State.Index)));
}
}
}
}
if (choicePassed)
{
yield return(ParseStep.Pass(this, matchedText, initialState, engine.State));
yield return(ParseStep.Break(this)); // TODO: lazy quantifiers might act in a similar manner as alternation here...
yield return(ParseStep.Backtrack(this, initialState, engine.State));
}
else
{
if (engine.State.Index != initialState.Index)
{
yield return(ParseStep.ResetIndex(this, initialState, engine.State));
engine.State = initialState;
}
}
choiceIndex++;
}
yield return(ParseStep.Fail(this, initialState, engine.State));
yield return(ParseStep.Break(this));
}