completion

private static async Task<CompletionResult> GetCompletionData(ScriptEditorControl parent, CancellationToken cancellationToken = default(CancellationToken))
{
    if (!parent.ContainsScript)
        return null;

    var doc = parent.GetScriptDocument();
    var model = await doc.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
    var syntax = await doc.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);

    var text = parent.GetScriptView().CurrentText;
    var position = parent.txtEditor.SelectionStart;
    var token = syntax.FindToken(position);
    var completionSpan = token.Span;

    if (position < completionSpan.Start)
        completionSpan = new TextSpan(position, 0);

    if (completionSpan.Length > 0 && position == completionSpan.End && !IsCompletionWordCharacter(text[position - 1]))
        completionSpan = new TextSpan(position, 0);

    var filterText = text.ToString(TextSpan.FromBounds(completionSpan.Start, position));

    var data = Recommender.GetRecommendedSymbolsAtPosition(model, completionSpan.Start, parent.GetScriptWorkspace(), null, cancellationToken)
        .Where(symbol => symbol.Name.IndexOf(filterText, StringComparison.InvariantCultureIgnoreCase) >= 0)
        .GroupBy(x => new SymbolGroupKey(x))
        .OrderByDescending(x => x.Key.Name.StartsWith(filterText, StringComparison.InvariantCultureIgnoreCase))
        .ThenBy(x => x.Key.Name)
        .ToImmutableArray();

    if (data.Length == 0)
        return null;

    return new CompletionResult(completionSpan, data);
}