TreeDrawer.cs

public static class TreeDrawer
{
    /// <summary>
    /// Output a Tree to the console
    /// </summary>
    /// <remarks>
    /// Example Output:
    /// 
    /// NodeName
    /// ├─ NodeName
    /// ├─ NodeName
    /// │    ├─ NodeName
    /// │    ├─ NodeName
    /// │    │    ├─ NodeName
    /// │    │    └─ NodeName
    /// │    └─ NodeName
    /// └ NodeName
    /// </remarks>
    /// <typeparam name="T"></typeparam>
    /// <param name="rootNode">The root node of the tree</param>
    /// <param name="getNodeName">A func that gets the Name of the node</param>
    /// <param name="getNodeChildren">A func that gets the Children of the node. Must have an indexer.</param>
    /// <param name="outputFunc">A func to which we'll send characters as we go. For Console output, use <see cref="Console.Write(string)"/>. Newlines will be sent as \r\n.</param>
    public static void DrawTree<T>(T rootNode, Func<T, string> getNodeName, Func<T, IList<T>> getNodeChildren, Action<string> outputFunc)
    {
        DrawTreeNode(rootNode, getNodeName, getNodeChildren, outputFunc, 0, new HashSet<int>());
    }

    private static void DrawTreeNode<T>(T node, Func<T, string> getNodeName, Func<T, IList<T>> getNodeChildren, Action<string> outputFunc, int currentIndent, HashSet<int> columnsThatHaveEnded)
    {
        const string HBar = "│";
        const string NodeWithFutureSiblings = "├─ ";
        const string NodeWithoutFutureSiblings = "└─ ";
        const string ColumnSpacing = "    ";

        for (int i = 0; i < currentIndent - 1; i++)
        {
            outputFunc(columnsThatHaveEnded.Contains(i) ? " " : HBar);
            outputFunc(ColumnSpacing);
        }

        if (currentIndent > 0)
        {
            outputFunc(columnsThatHaveEnded.Contains(currentIndent - 1) ? NodeWithoutFutureSiblings : NodeWithFutureSiblings);
        }

        outputFunc(getNodeName(node));
        outputFunc("\r\n");

        var children = getNodeChildren(node);
        var cc = children?.Count;
        if (cc.HasValue && cc.Value > 0)
        {
            for (int ix = 0; ix < cc.Value; ix++)
            {
                var child = children[ix];

                if (ix == cc.Value - 1)
                {
                    columnsThatHaveEnded.Add(currentIndent);
                }

                DrawTreeNode(child, getNodeName, getNodeChildren, outputFunc, currentIndent + 1, columnsThatHaveEnded);
            }

            // Reset for the next sibling, since the HashSet is shared between siblings
            columnsThatHaveEnded.Remove(currentIndent);
        }
    }
}