//#r "nuget: System.CommandLine, 2.0.0-beta1.20253.1"

using System;

using System.CommandLine;

using System.CommandLine.Binding;

using System.CommandLine.Invocation;

using System.ComponentModel;

using System.ComponentModel.DataAnnotations;

using System.Linq;

using System.Reflection;

​

public static class Program

{

    public static int Main(string[] args)

    {

        args = new string[] {

            "-Name", "Paul",

            "-Message", DateTime.Now+" > Hello {0}!", 

        };

        var command = new RootCommand();

        command.ConfigureFromClass<Hello>(hello =>

        {

            Console.WriteLine(hello.Speak());

        });

​

        return command.Invoke(args);

        //DotNetFiddle might display strange error:

        //    Fatal Error: Execution time limit was exceeded

        //    I'm not sure why but it is fine in Visual Studio :(

    }

​

    [Description("Say Hello")]

    public class Hello

    {

        [Description("Someone's name")]

        public string Name { get; set; }

​

        [Description("A simple message"), Required]

        public string Message { get; set; }

​

        public string Speak()

        {

            return string.Format(Message, Name);

        }

    }

​

    public static void ConfigureFromClass<T>(this Command command, Action<T> execute)

        where T : new()

    {

        var commandType = typeof(T);

        command.Description = commandType

            .GetCustomAttributes()

            .OfType<DescriptionAttribute>()

            .FirstOrDefault()

            ?.Description;

        var props = commandType.GetProperties();

        foreach (var prop in props)

        {

            var description = prop.GetAttribute<DescriptionAttribute>()?.Description;

            var required = prop.GetAttribute<RequiredAttribute>() != null;

            var option = new Option($"-{prop.Name}", description)

            {

                Required = required, 

            };

            option.Argument = new Argument{ArgumentType = prop.PropertyType, };

            command.AddOption(option);

        }

​

        command.Handler = CommandHandler.Create((InvocationContext context) =>

        {

            var modelBinder = new ModelBinder<T>();

            var cmd = new T();

            modelBinder.UpdateInstance(cmd, context.BindingContext);

            execute(cmd);

        });

    }

​

    public static T GetAttribute<T>(this PropertyInfo prop)

    {

        return prop.GetCustomAttributes().OfType<T>().FirstOrDefault();

    }

}