Converts a type/enum name to a string as sentence case.

TypeNameToString.cs

using System;
using System.Text;

public static class TypeNameToString
{
    public static string TypeNameToString(this string text)
    {
        var builder = new StringBuilder();
        var typeName = text;
        int index = -1;

        while (++index < typeName.Length)
        {
            char nextChar = typeName[index];
            if (char.IsUpper(nextChar) && index != 0)
            {
                if (char.IsLower(typeName[index - 1]))
                {
                    if (typeName.Length > index + 1 &&
                        char.IsLower(typeName[index + 1]))
                    {
                        nextChar = char.ToLower(nextChar);
                    }
                    builder.Append(' ');
                }
                else if (typeName.Length > index + 1 &&
                         char.IsLower(typeName[index + 1]))
                {
                    builder.Append(' ');
                    nextChar = char.ToLower(nextChar);
                }
            }
            builder.Append(nextChar);
        }

        return builder.ToString();
    }

    public static string ToNiceString<TEnum>(this TEnum val)
        where TEnum : struct, IConvertible, IComparable, IFormattable
    {
        if (!typeof(TEnum).IsEnum)
        {
            throw new ArgumentException("TEnum must be an enum.");
        }

        return Enum.GetName(typeof(TEnum), val).TypeNameToString();
    }

    public static string ToNiceString(this Type type)
    {
        return type.Name.TypeNameToString();
    }
}