Antlr4.Tool.Grammar.GetStateToGrammarRegionMap C# (CSharp) Method

        public static IDictionary<int, Interval> GetStateToGrammarRegionMap(GrammarRootAST ast, IntervalSet grammarTokenTypes)
        {
            IDictionary<int, Interval> stateToGrammarRegionMap = new Dictionary<int, Interval>();
            if (ast == null)
                return stateToGrammarRegionMap;

            IList<GrammarAST> nodes = ast.GetNodesWithType(grammarTokenTypes);
            foreach (GrammarAST n in nodes)
            {
                if (n.atnState != null)
                {
                    Interval tokenRegion = Interval.Of(n.TokenStartIndex, n.TokenStopIndex);
                    Antlr.Runtime.Tree.ITree ruleNode = null;
                    // RULEs, BLOCKs of transformed recursive rules point to original token interval
                    switch (n.Type)
                    {
                    case ANTLRParser.RULE:
                        ruleNode = n;
                        break;
                    case ANTLRParser.BLOCK:
                    case ANTLRParser.CLOSURE:
                        ruleNode = n.GetAncestor(ANTLRParser.RULE);
                        break;
                    }
                    if (ruleNode is RuleAST)
                    {
                        string ruleName = ((RuleAST)ruleNode).GetRuleName();
                        Rule r = ast.g.GetRule(ruleName);
                        if (r is LeftRecursiveRule)
                        {
                            RuleAST originalAST = ((LeftRecursiveRule)r).GetOriginalAST();
                            tokenRegion = Interval.Of(originalAST.TokenStartIndex, originalAST.TokenStopIndex);
                        }
                    }
                    stateToGrammarRegionMap[n.atnState.stateNumber] = tokenRegion;
                }
            }
            return stateToGrammarRegionMap;
        }