some poor initial progress on command trees

src/console/Program.cs

@@ -1,12 +1,154 @@
 using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using CommandLine;
+using CommandLine.Text;
 
 namespace Shamir
 {
+    public class CdnOperations : ICommandSet
+    {
+        [Verb("ls", HelpText = "List files on the CDN")]
+        public class CdnLsOptions
+        {
+        }
+
+        [Verb("add", HelpText = "Upload a file to the CDN")]
+        public class CdnAddOptions
+        {
+        }
+
+        [Verb("mv", HelpText = "Move a file to the CDN")]
+        public class CdnMvOptions
+        {
+        }
+
+        public static IEnumerable<Type> VerbOptionTypes
+        {
+            get
+            {
+                yield return typeof(CdnLsOptions);
+                yield return typeof(CdnAddOptions);
+                yield return typeof(CdnMvOptions);
+            }
+        }
+
+        public ICommand? FindCommand(ReadOnlySpan<string> args)
+        {
+            if (args.Length == 0) return null;
+
+            var parserResult = Parser.Default.ParseArguments<CdnLsOptions, CdnAddOptions, CdnMvOptions>(args.ToArray());
+            return parserResult.MapResult<CdnLsOptions, CdnAddOptions, CdnMvOptions, ICommand>(
+                options => new CdnLsCommand(options),
+                options => new CdnAddCommand(options),
+                options => new CdnMvCommand(options),
+                errors => new HelpTextCommand(parserResult)
+            );
+        }
+
+        public class CdnLsCommand : ICommand
+        {
+            public CdnLsCommand(CdnLsOptions options)
+            {
+            }
+
+            public ValueTask<int> ExecuteAsync()
+            {
+                Console.WriteLine($"Executing: cdn-ls");
+                return ValueTask.FromResult(0);
+            }
+        }
+
+        public class CdnAddCommand : ICommand
+        {
+            public CdnAddCommand(CdnAddOptions options)
+            {
+            }
+            
+            public ValueTask<int> ExecuteAsync()
+            {
+                Console.WriteLine($"Executing: cdn-add");
+                return ValueTask.FromResult(0);
+            }
+        }
+
+        public class CdnMvCommand : ICommand
+        {
+            public CdnMvCommand(CdnMvOptions options)
+            {
+            }
+            
+            public ValueTask<int> ExecuteAsync()
+            {
+                Console.WriteLine($"Executing: cdn-mv");
+                return ValueTask.FromResult(0);
+            }
+        }
+
+        public class HelpTextCommand : ICommand
+        {
+            public HelpTextCommand(ParserResult<object> result)
+            {
+                this.result = result ?? throw new ArgumentNullException(nameof(result));
+                Debug.Assert(result.Tag == ParserResultType.NotParsed);
+            }
+
+            readonly ParserResult<object> result;
+
+            public ValueTask<int> ExecuteAsync()
+            {
+                var helpText = HelpText.AutoBuild(result);
+                Console.Error.WriteLine(helpText);
+                return ValueTask.FromResult(1);
+            }
+        }
+    }
+
+    public interface ICommand
+    {
+        ValueTask<int> ExecuteAsync();
+    }
+
+    public interface ICommandSet
+    {
+        ICommand? FindCommand(ReadOnlySpan<string> args);
+        static IEnumerable<Type> VerbOptionTypes { get; }
+    }
+
+    public class CommandTree : ICommandSet
+    {
+        IEnumerable<Type> VerbOptionTypes { get; }
+        public ICommand? FindCommand(ReadOnlySpan<string> args)
+        {
+            if (args.Length == 0) return null;
+
+            return args[0] switch {
+                "cdn" => new CdnOperations().FindCommand(args[1..]),
+                _ => null,
+            };
+        }
+    }
+
     class Program
     {
-        static void Main(string[] args)
+        public static async Task<int> Main(string[] args)
         {
-            Console.WriteLine("Hello World!");
+            var tree = new CommandTree();
+            var command = tree.FindCommand(args);
+            if (command is null)
+            {
+                PrintHelpText(tree);
+                return 1;
+            }
+
+            return await command.ExecuteAsync();
+        }
+        
+        static void PrintHelpText(ICommandSet tree)
+        {
+
         }
     }
 }