Antlr4.Runtime.Atn.ArrayPredictionContext.AppendContext C# (CSharp) Method

        private static PredictionContext AppendContext(PredictionContext context, PredictionContext suffix, PredictionContext.IdentityHashMap visited)
        {
            if (suffix.IsEmpty)
            {
                if (IsEmptyLocal(suffix))
                {
                    if (context.HasEmpty)
                    {
                        return EmptyLocal;
                    }
                    throw new NotSupportedException("what to do here?");
                }
                return context;
            }
            if (suffix.Size != 1)
            {
                throw new NotSupportedException("Appending a tree suffix is not yet supported.");
            }
            PredictionContext result;
            if (!visited.TryGetValue(context, out result))
            {
                if (context.IsEmpty)
                {
                    result = suffix;
                }
                else
                {
                    int parentCount = context.Size;
                    if (context.HasEmpty)
                    {
                        parentCount--;
                    }
                    PredictionContext[] updatedParents = new PredictionContext[parentCount];
                    int[] updatedReturnStates = new int[parentCount];
                    for (int i = 0; i < parentCount; i++)
                    {
                        updatedReturnStates[i] = context.GetReturnState(i);
                    }
                    for (int i_1 = 0; i_1 < parentCount; i_1++)
                    {
                        updatedParents[i_1] = AppendContext(context.GetParent(i_1), suffix, visited);
                    }
                    if (updatedParents.Length == 1)
                    {
                        result = new SingletonPredictionContext(updatedParents[0], updatedReturnStates[0]);
                    }
                    else
                    {
                        System.Diagnostics.Debug.Assert(updatedParents.Length > 1);
                        result = new Antlr4.Runtime.Atn.ArrayPredictionContext(updatedParents, updatedReturnStates);
                    }
                    if (context.HasEmpty)
                    {
                        result = PredictionContext.Join(result, suffix);
                    }
                }
                visited[context] = result;
            }
            return result;
        }