//
// Options.cs
//
// Authors:
//  Jonathan Pryor <jpryor@novell.com>, <Jonathan.Pryor@microsoft.com>
//  Federico Di Gregorio <fog@initd.org>
//  Rolf Bjarne Kvinge <rolf@xamarin.com>
//
// Copyright (C) 2008 Novell (http://www.novell.com)
// Copyright (C) 2009 Federico Di Gregorio.
// Copyright (C) 2012 Xamarin Inc (http://www.xamarin.com)
// Copyright (C) 2017 Microsoft Corporation (http://www.microsoft.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

// Compile With:
//   mcs -debug+ -r:System.Core Options.cs -o:Mono.Options.dll -t:library
//   mcs -debug+ -d:LINQ -r:System.Core Options.cs -o:Mono.Options.dll -t:library
//
// The LINQ version just changes the implementation of
// OptionSet.Parse(IEnumerable<string>), and confers no semantic changes.

//
// A Getopt::Long-inspired option parsing library for C#.
//
// Mono.Options.OptionSet is built upon a key/value table, where the
// key is a option format string and the value is a delegate that is 
// invoked when the format string is matched.
//
// Option format strings:
//  Regex-like BNF Grammar: 
//    name: .+
//    type: [=:]
//    sep: ( [^{}]+ | '{' .+ '}' )?
//    aliases: ( name type sep ) ( '|' name type sep )*
// 
// Each '|'-delimited name is an alias for the associated action.  If the
// format string ends in a '=', it has a required value.  If the format
// string ends in a ':', it has an optional value.  If neither '=' or ':'
// is present, no value is supported.  `=' or `:' need only be defined on one
// alias, but if they are provided on more than one they must be consistent.
//
// Each alias portion may also end with a "key/value separator", which is used
// to split option values if the option accepts > 1 value.  If not specified,
// it defaults to '=' and ':'.  If specified, it can be any character except
// '{' and '}' OR the *string* between '{' and '}'.  If no separator should be
// used (i.e. the separate values should be distinct arguments), then "{}"
// should be used as the separator.
//
// Options are extracted either from the current option by looking for
// the option name followed by an '=' or ':', or is taken from the
// following option IFF:
//  - The current option does not contain a '=' or a ':'
//  - The current option requires a value (i.e. not a Option type of ':')
//
// The `name' used in the option format string does NOT include any leading
// option indicator, such as '-', '--', or '/'.  All three of these are
// permitted/required on any named option.
//
// Option bundling is permitted so long as:
//   - '-' is used to start the option group
//   - all of the bundled options are a single character
//   - at most one of the bundled options accepts a value, and the value
//     provided starts from the next character to the end of the string.
//
// This allows specifying '-a -b -c' as '-abc', and specifying '-D name=value'
// as '-Dname=value'.
//
// Option processing is disabled by specifying "--".  All options after "--"
// are returned by OptionSet.Parse() unchanged and unprocessed.
//
// Unprocessed options are returned from OptionSet.Parse().
//
// Examples:
//  int verbose = 0;
//  OptionSet p = new OptionSet ()
//    .Add ("v", v => ++verbose)
//    .Add ("name=|value=", v => Console.WriteLine (v));
//  p.Parse (new string[]{"-v", "--v", "/v", "-name=A", "/name", "B", "extra"});
//
// The above would parse the argument string array, and would invoke the
// lambda expression three times, setting `verbose' to 3 when complete.  
// It would also print out "A" and "B" to standard output.
// The returned array would contain the string "extra".
//
// C# 3.0 collection initializers are supported and encouraged:
//  var p = new OptionSet () {
//    { "h|?|help", v => ShowHelp () },
//  };
//
// System.ComponentModel.TypeConverter is also supported, allowing the use of
// custom data types in the callback type; TypeConverter.ConvertFromString()
// is used to convert the value option to an instance of the specified
// type:
//
//  var p = new OptionSet () {
//    { "foo=", (Foo f) => Console.WriteLine (f.ToString ()) },
//  };
//
// Random other tidbits:
//  - Boolean options (those w/o '=' or ':' in the option format string)
//    are explicitly enabled if they are followed with '+', and explicitly
//    disabled if they are followed with '-':
//      string a = null;
//      var p = new OptionSet () {
//        { "a", s => a = s },
//      };
//      p.Parse (new string[]{"-a"});   // sets v != null
//      p.Parse (new string[]{"-a+"});  // sets v != null
//      p.Parse (new string[]{"-a-"});  // sets v == null
//

//
// Mono.Options.CommandSet allows easily having separate commands and
// associated command options, allowing creation of a *suite* along the
// lines of **git**(1), **svn**(1), etc.
//
// CommandSet allows intermixing plain text strings for `--help` output,
// Option values -- as supported by OptionSet -- and Command instances,
// which have a name, optional help text, and an optional OptionSet.
//
//  var suite = new CommandSet ("suite-name") {
//    // Use strings and option values, as with OptionSet
//    "usage: suite-name COMMAND [OPTIONS]+",
//    { "v:", "verbosity", (int? v) => Verbosity = v.HasValue ? v.Value : Verbosity+1 },
//    // Commands may also be specified
//    new Command ("command-name", "command help") {
//      Options = new OptionSet {/*...*/},
//      Run     = args => { /*...*/},
//    },
//    new MyCommandSubclass (),
//  };
//  return suite.Run (new string[]{...});
//
// CommandSet provides a `help` command, and forwards `help COMMAND`
// to the registered Command instance by invoking Command.Invoke()
// with `--help` as an option.
//

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Globalization;
using System.IO;
#if PCL
using System.Reflection;
#else
using System.Runtime.Serialization;
using System.Security.Permissions;
#endif
using System.Text;
using System.Text.RegularExpressions;

#if LINQ
using System.Linq;
#endif

#if TEST
using NDesk.Options;
#endif

#if PCL
using MessageLocalizerConverter = System.Func<string, string>;
#else
using MessageLocalizerConverter = System.Converter<string, string>;
#endif

#if NDESK_OPTIONS
namespace NDesk.Options
#else
namespace Mono.Options
#endif
{
	static class StringCoda {

		public static IEnumerable<string> WrappedLines (string self, params int[] widths)
		{
			IEnumerable<int> w = widths;
			return WrappedLines (self, w);
		}

		public static IEnumerable<string> WrappedLines (string self, IEnumerable<int> widths)
		{
			if (widths == null)
				throw new ArgumentNullException ("widths");
			return CreateWrappedLinesIterator (self, widths);
		}

		private static IEnumerable<string> CreateWrappedLinesIterator (string self, IEnumerable<int> widths)
		{
			if (string.IsNullOrEmpty (self)) {
				yield return string.Empty;
				yield break;
			}
			using (IEnumerator<int> ewidths = widths.GetEnumerator ()) {
				bool? hw = null;
				int width = GetNextWidth (ewidths, int.MaxValue, ref hw);
				int start = 0, end;
				do {
					end = GetLineEnd (start, width, self);
					char c = self [end-1];
					if (char.IsWhiteSpace (c))
						--end;
					bool needContinuation = end != self.Length && !IsEolChar (c);
					string continuation = "";
					if (needContinuation) {
						--end;
						continuation = "-";
					}
					string line = self.Substring (start, end - start) + continuation;
					yield return line;
					start = end;
					if (char.IsWhiteSpace (c))
						++start;
					width = GetNextWidth (ewidths, width, ref hw);
				} while (start < self.Length);
			}
		}

		private static int GetNextWidth (IEnumerator<int> ewidths, int curWidth, ref bool? eValid)
		{
			if (!eValid.HasValue || (eValid.HasValue && eValid.Value)) {
				curWidth = (eValid = ewidths.MoveNext ()).Value ? ewidths.Current : curWidth;
				// '.' is any character, - is for a continuation
				const string minWidth = ".-";
				if (curWidth < minWidth.Length)
					throw new ArgumentOutOfRangeException ("widths",
							string.Format ("Element must be >= {0}, was {1}.", minWidth.Length, curWidth));
				return curWidth;
			}
			// no more elements, use the last element.
			return curWidth;
		}

		private static bool IsEolChar (char c)
		{
			return !char.IsLetterOrDigit (c);
		}

		private static int GetLineEnd (int start, int length, string description)
		{
			int end = System.Math.Min (start + length, description.Length);
			int sep = -1;
			for (int i = start; i < end; ++i) {
				if (description [i] == '\n')
					return i+1;
				if (IsEolChar (description [i]))
					sep = i+1;
			}
			if (sep == -1 || end == description.Length)
				return end;
			return sep;
		}
	}

	public class OptionValueCollection : IList, IList<string> {

		List<string> values = new List<string> ();
		OptionContext c;

		internal OptionValueCollection (OptionContext c)
		{
			this.c = c;
		}

		#region ICollection
		void ICollection.CopyTo (Array array, int index)  {(values as ICollection).CopyTo (array, index);}
		bool ICollection.IsSynchronized                   {get {return (values as ICollection).IsSynchronized;}}
		object ICollection.SyncRoot                       {get {return (values as ICollection).SyncRoot;}}
		#endregion

		#region ICollection<T>
		public void Add (string item)                       {values.Add (item);}
		public void Clear ()                                {values.Clear ();}
		public bool Contains (string item)                  {return values.Contains (item);}
		public void CopyTo (string[] array, int arrayIndex) {values.CopyTo (array, arrayIndex);}
		public bool Remove (string item)                    {return values.Remove (item);}
		public int Count                                    {get {return values.Count;}}
		public bool IsReadOnly                              {get {return false;}}
		#endregion

		#region IEnumerable
		IEnumerator IEnumerable.GetEnumerator () {return values.GetEnumerator ();}
		#endregion

		#region IEnumerable<T>
		public IEnumerator<string> GetEnumerator () {return values.GetEnumerator ();}
		#endregion

		#region IList
		int IList.Add (object value)                {return (values as IList).Add (value);}
		bool IList.Contains (object value)          {return (values as IList).Contains (value);}
		int IList.IndexOf (object value)            {return (values as IList).IndexOf (value);}
		void IList.Insert (int index, object value) {(values as IList).Insert (index, value);}
		void IList.Remove (object value)            {(values as IList).Remove (value);}
		void IList.RemoveAt (int index)             {(values as IList).RemoveAt (index);}
		bool IList.IsFixedSize                      {get {return false;}}
		object IList.this [int index]               {get {return this [index];} set {(values as IList)[index] = value;}}
		#endregion

		#region IList<T>
		public int IndexOf (string item)            {return values.IndexOf (item);}
		public void Insert (int index, string item) {values.Insert (index, item);}
		public void RemoveAt (int index)            {values.RemoveAt (index);}

		private void AssertValid (int index)
		{
			if (c.Option == null)
				throw new InvalidOperationException ("OptionContext.Option is null.");
			if (index >= c.Option.MaxValueCount)
				throw new ArgumentOutOfRangeException ("index");
			if (c.Option.OptionValueType == OptionValueType.Required &&
					index >= values.Count)
				throw new OptionException (string.Format (
							c.OptionSet.MessageLocalizer ("Missing required value for option '{0}'."), c.OptionName), 
						c.OptionName);
		}

		public string this [int index] {
			get {
				AssertValid (index);
				return index >= values.Count ? null : values [index];
			}
			set {
				values [index] = value;
			}
		}
		#endregion

		public List<string> ToList ()
		{
			return new List<string> (values);
		}

		public string[] ToArray ()
		{
			return values.ToArray ();
		}

		public override string ToString ()
		{
			return string.Join (", ", values.ToArray ());
		}
	}

	public class OptionContext {
		private Option                option;
		private string                name;
		private int                   index;
		private OptionSet             set;
		private OptionValueCollection c;

		public OptionContext (OptionSet set)
		{
			this.set = set;
			this.c   = new OptionValueCollection (this);
		}

		public Option Option {
			get {return option;}
			set {option = value;}
		}

		public string OptionName { 
			get {return name;}
			set {name = value;}
		}

		public int OptionIndex {
			get {return index;}
			set {index = value;}
		}

		public OptionSet OptionSet {
			get {return set;}
		}

		public OptionValueCollection OptionValues {
			get {return c;}
		}
	}

	public enum OptionValueType {
		None, 
		Optional,
		Required,
	}

	public abstract class Option {
		string prototype, description;
		string[] names;
		OptionValueType type;
		int count;
		string[] separators;
		bool hidden;

		protected Option (string prototype, string description)
			: this (prototype, description, 1, false)
		{
		}

		protected Option (string prototype, string description, int maxValueCount)
			: this (prototype, description, maxValueCount, false)
		{
		}

		protected Option (string prototype, string description, int maxValueCount, bool hidden)
		{
			if (prototype == null)
				throw new ArgumentNullException ("prototype");
			if (prototype.Length == 0)
				throw new ArgumentException ("Cannot be the empty string.", "prototype");
			if (maxValueCount < 0)
				throw new ArgumentOutOfRangeException ("maxValueCount");

			this.prototype   = prototype;
			this.description = description;
			this.count       = maxValueCount;
			this.names       = (this is OptionSet.Category)
				// append GetHashCode() so that "duplicate" categories have distinct
				// names, e.g. adding multiple "" categories should be valid.
				? new[]{prototype + this.GetHashCode ()}
				: prototype.Split ('|');

			if (this is OptionSet.Category || this is CommandOption)
				return;

			this.type        = ParsePrototype ();
			this.hidden      = hidden;

			if (this.count == 0 && type != OptionValueType.None)
				throw new ArgumentException (
						"Cannot provide maxValueCount of 0 for OptionValueType.Required or " +
							"OptionValueType.Optional.",
						"maxValueCount");
			if (this.type == OptionValueType.None && maxValueCount > 1)
				throw new ArgumentException (
						string.Format ("Cannot provide maxValueCount of {0} for OptionValueType.None.", maxValueCount),
						"maxValueCount");
			if (Array.IndexOf (names, "<>") >= 0 && 
					((names.Length == 1 && this.type != OptionValueType.None) ||
					 (names.Length > 1 && this.MaxValueCount > 1)))
				throw new ArgumentException (
						"The default option handler '<>' cannot require values.",
						"prototype");
		}

		public string           Prototype       {get {return prototype;}}
		public string           Description     {get {return description;}}
		public OptionValueType  OptionValueType {get {return type;}}
		public int              MaxValueCount   {get {return count;}}
		public bool             Hidden          {get {return hidden;}}

		public string[] GetNames ()
		{
			return (string[]) names.Clone ();
		}

		public string[] GetValueSeparators ()
		{
			if (separators == null)
				return new string [0];
			return (string[]) separators.Clone ();
		}

		protected static T Parse<T> (string value, OptionContext c)
		{
			Type tt = typeof (T);
#if PCL
			TypeInfo ti = tt.GetTypeInfo ();
#else
			Type ti = tt;
#endif
			bool nullable = 
				ti.IsValueType && 
				ti.IsGenericType && 
				!ti.IsGenericTypeDefinition && 
				ti.GetGenericTypeDefinition () == typeof (Nullable<>);
#if PCL
			Type targetType = nullable ? tt.GenericTypeArguments [0] : tt;
#else
			Type targetType = nullable ? tt.GetGenericArguments () [0] : tt;
#endif
			T t = default (T);
			try {
				if (value != null) {
#if PCL
					if (targetType.GetTypeInfo ().IsEnum)
						t = (T) Enum.Parse (targetType, value, true);
					else
						t = (T) Convert.ChangeType (value, targetType);
#else
					TypeConverter conv = TypeDescriptor.GetConverter (targetType);
					t = (T) conv.ConvertFromString (value);
#endif
				}
			}
			catch (Exception e) {
				throw new OptionException (
						string.Format (
							c.OptionSet.MessageLocalizer ("Could not convert string `{0}' to type {1} for option `{2}'."),
							value, targetType.Name, c.OptionName),
						c.OptionName, e);
			}
			return t;
		}

		internal string[] Names           {get {return names;}}
		internal string[] ValueSeparators {get {return separators;}}

		static readonly char[] NameTerminator = new char[]{'=', ':'};

		private OptionValueType ParsePrototype ()
		{
			char type = '\0';
			List<string> seps = new List<string> ();
			for (int i = 0; i < names.Length; ++i) {
				string name = names [i];
				if (name.Length == 0)
					throw new ArgumentException ("Empty option names are not supported.", "prototype");

				int end = name.IndexOfAny (NameTerminator);
				if (end == -1)
					continue;
				names [i] = name.Substring (0, end);
				if (type == '\0' || type == name [end])
					type = name [end];
				else 
					throw new ArgumentException (
							string.Format ("Conflicting option types: '{0}' vs. '{1}'.", type, name [end]),
							"prototype");
				AddSeparators (name, end, seps);
			}

			if (type == '\0')
				return OptionValueType.None;

			if (count <= 1 && seps.Count != 0)
				throw new ArgumentException (
						string.Format ("Cannot provide key/value separators for Options taking {0} value(s).", count),
						"prototype");
			if (count > 1) {
				if (seps.Count == 0)
					this.separators = new string[]{":", "="};
				else if (seps.Count == 1 && seps [0].Length == 0)
					this.separators = null;
				else
					this.separators = seps.ToArray ();
			}

			return type == '=' ? OptionValueType.Required : OptionValueType.Optional;
		}

		private static void AddSeparators (string name, int end, ICollection<string> seps)
		{
			int start = -1;
			for (int i = end+1; i < name.Length; ++i) {
				switch (name [i]) {
					case '{':
						if (start != -1)
							throw new ArgumentException (
									string.Format ("Ill-formed name/value separator found in \"{0}\".", name),
									"prototype");
						start = i+1;
						break;
					case '}':
						if (start == -1)
							throw new ArgumentException (
									string.Format ("Ill-formed name/value separator found in \"{0}\".", name),
									"prototype");
						seps.Add (name.Substring (start, i-start));
						start = -1;
						break;
					default:
						if (start == -1)
							seps.Add (name [i].ToString ());
						break;
				}
			}
			if (start != -1)
				throw new ArgumentException (
						string.Format ("Ill-formed name/value separator found in \"{0}\".", name),
						"prototype");
		}

		public void Invoke (OptionContext c)
		{
			OnParseComplete (c);
			c.OptionName  = null;
			c.Option      = null;
			c.OptionValues.Clear ();
		}

		protected abstract void OnParseComplete (OptionContext c);

		internal void InvokeOnParseComplete (OptionContext c)
		{
			OnParseComplete (c);
		}

		public override string ToString ()
		{
			return Prototype;
		}
	}

	public abstract class ArgumentSource {

		protected ArgumentSource ()
		{
		}

		public abstract string[] GetNames ();
		public abstract string Description { get; }
		public abstract bool GetArguments (string value, out IEnumerable<string> replacement);

#if !PCL || NETSTANDARD1_3
		public static IEnumerable<string> GetArgumentsFromFile (string file)
		{
			return GetArguments (File.OpenText (file), true);
		}
#endif

		public static IEnumerable<string> GetArguments (TextReader reader)
		{
			return GetArguments (reader, false);
		}

		// Cribbed from mcs/driver.cs:LoadArgs(string)
		static IEnumerable<string> GetArguments (TextReader reader, bool close)
		{
			try {
				StringBuilder arg = new StringBuilder ();

				string line;
				while ((line = reader.ReadLine ()) != null) {
					int t = line.Length;

					for (int i = 0; i < t; i++) {
						char c = line [i];
						
						if (c == '"' || c == '\'') {
							char end = c;
							
							for (i++; i < t; i++){
								c = line [i];

								if (c == end)
									break;
								arg.Append (c);
							}
						} else if (c == ' ') {
							if (arg.Length > 0) {
								yield return arg.ToString ();
								arg.Length = 0;
							}
						} else
							arg.Append (c);
					}
					if (arg.Length > 0) {
						yield return arg.ToString ();
						arg.Length = 0;
					}
				}
			}
			finally {
				if (close)
					reader.Dispose ();
			}
		}
	}

#if !PCL || NETSTANDARD1_3
	public class ResponseFileSource : ArgumentSource {

		public override string[] GetNames ()
		{
			return new string[]{"@file"};
		}

		public override string Description {
			get {return "Read response file for more options.";}
		}

		public override bool GetArguments (string value, out IEnumerable<string> replacement)
		{
			if (string.IsNullOrEmpty (value) || !value.StartsWith ("@")) {
				replacement = null;
				return false;
			}
			replacement = ArgumentSource.GetArgumentsFromFile (value.Substring (1));
			return true;
		}
	}
#endif

#if !PCL
	[Serializable]
#endif
	public class OptionException : Exception {
		private string option;

		public OptionException ()
		{
		}

		public OptionException (string message, string optionName)
			: base (message)
		{
			this.option = optionName;
		}

		public OptionException (string message, string optionName, Exception innerException)
			: base (message, innerException)
		{
			this.option = optionName;
		}

#if !PCL
		protected OptionException (SerializationInfo info, StreamingContext context)
			: base (info, context)
		{
			this.option = info.GetString ("OptionName");
		}
#endif

		public string OptionName {
			get {return this.option;}
		}

#if !PCL
#pragma warning disable 618 // SecurityPermissionAttribute is obsolete
		[SecurityPermission (SecurityAction.LinkDemand, SerializationFormatter = true)]
#pragma warning restore 618
		public override void GetObjectData (SerializationInfo info, StreamingContext context)
		{
			base.GetObjectData (info, context);
			info.AddValue ("OptionName", option);
		}
#endif
	}

	public delegate void OptionAction<TKey, TValue> (TKey key, TValue value);

	public class OptionSet : KeyedCollection<string, Option>
	{
		public OptionSet ()
			: this (null)
		{
		}

		public OptionSet (MessageLocalizerConverter localizer)
		{
			this.roSources = new ReadOnlyCollection<ArgumentSource> (sources);
			this.localizer = localizer;
			if (this.localizer == null) {
				this.localizer = delegate (string f) {
					return f;
				};
			}
		}

		MessageLocalizerConverter localizer;

		public MessageLocalizerConverter MessageLocalizer {
			get {return localizer;}
			internal set {localizer = value;}
		}

		List<ArgumentSource> sources = new List<ArgumentSource> ();
		ReadOnlyCollection<ArgumentSource> roSources;

		public ReadOnlyCollection<ArgumentSource> ArgumentSources {
			get {return roSources;}
		}


		protected override string GetKeyForItem (Option item)
		{
			if (item == null)
				throw new ArgumentNullException ("option");
			if (item.Names != null && item.Names.Length > 0)
				return item.Names [0];
			// This should never happen, as it's invalid for Option to be
			// constructed w/o any names.
			throw new InvalidOperationException ("Option has no names!");
		}

		[Obsolete ("Use KeyedCollection.this[string]")]
		protected Option GetOptionForName (string option)
		{
			if (option == null)
				throw new ArgumentNullException ("option");
			try {
				return base [option];
			}
			catch (KeyNotFoundException) {
				return null;
			}
		}

		protected override void InsertItem (int index, Option item)
		{
			base.InsertItem (index, item);
			AddImpl (item);
		}

		protected override void RemoveItem (int index)
		{
			Option p = Items [index];
			base.RemoveItem (index);
			// KeyedCollection.RemoveItem() handles the 0th item
			for (int i = 1; i < p.Names.Length; ++i) {
				Dictionary.Remove (p.Names [i]);
			}
		}

		protected override void SetItem (int index, Option item)
		{
			base.SetItem (index, item);
			AddImpl (item);
		}

		private void AddImpl (Option option)
		{
			if (option == null)
				throw new ArgumentNullException ("option");
			List<string> added = new List<string> (option.Names.Length);
			try {
				// KeyedCollection.InsertItem/SetItem handle the 0th name.
				for (int i = 1; i < option.Names.Length; ++i) {
					Dictionary.Add (option.Names [i], option);
					added.Add (option.Names [i]);
				}
			}
			catch (Exception) {
				foreach (string name in added)
					Dictionary.Remove (name);
				throw;
			}
		}

		public OptionSet Add (string header)
		{
			if (header == null)
				throw new ArgumentNullException ("header");
			Add (new Category (header));
			return this;
		}

		internal sealed class Category : Option {

			// Prototype starts with '=' because this is an invalid prototype
			// (see Option.ParsePrototype(), and thus it'll prevent Category
			// instances from being accidentally used as normal options.
			public Category (string description)
				: base ("=:Category:= " + description, description)
			{
			}

			protected override void OnParseComplete (OptionContext c)
			{
				throw new NotSupportedException ("Category.OnParseComplete should not be invoked.");
			}
		}


		public new OptionSet Add (Option option)
		{
			base.Add (option);
			return this;
		}

		sealed class ActionOption : Option {
			Action<OptionValueCollection> action;

			public ActionOption (string prototype, string description, int count, Action<OptionValueCollection> action)
				: this (prototype, description, count, action, false)
			{
			}

			public ActionOption (string prototype, string description, int count, Action<OptionValueCollection> action, bool hidden)
				: base (prototype, description, count, hidden)
			{
				if (action == null)
					throw new ArgumentNullException ("action");
				this.action = action;
			}

			protected override void OnParseComplete (OptionContext c)
			{
				action (c.OptionValues);
			}
		}

		public OptionSet Add (string prototype, Action<string> action)
		{
			return Add (prototype, null, action);
		}

		public OptionSet Add (string prototype, string description, Action<string> action)
		{
			return Add (prototype, description, action, false);
		}

		public OptionSet Add (string prototype, string description, Action<string> action, bool hidden)
		{
			if (action == null)
				throw new ArgumentNullException ("action");
			Option p = new ActionOption (prototype, description, 1, 
					delegate (OptionValueCollection v) { action (v [0]); }, hidden);
			base.Add (p);
			return this;
		}

		public OptionSet Add (string prototype, OptionAction<string, string> action)
		{
			return Add (prototype, null, action);
		}

		public OptionSet Add (string prototype, string description, OptionAction<string, string> action)
		{
			return Add (prototype, description, action, false);
		}

		public OptionSet Add (string prototype, string description, OptionAction<string, string> action, bool hidden)	{
			if (action == null)
				throw new ArgumentNullException ("action");
			Option p = new ActionOption (prototype, description, 2, 
					delegate (OptionValueCollection v) {action (v [0], v [1]);}, hidden);
			base.Add (p);
			return this;
		}

		sealed class ActionOption<T> : Option {
			Action<T> action;

			public ActionOption (string prototype, string description, Action<T> action)
				: base (prototype, description, 1)
			{
				if (action == null)
					throw new ArgumentNullException ("action");
				this.action = action;
			}

			protected override void OnParseComplete (OptionContext c)
			{
				action (Parse<T> (c.OptionValues [0], c));
			}
		}

		sealed class ActionOption<TKey, TValue> : Option {
			OptionAction<TKey, TValue> action;

			public ActionOption (string prototype, string description, OptionAction<TKey, TValue> action)
				: base (prototype, description, 2)
			{
				if (action == null)
					throw new ArgumentNullException ("action");
				this.action = action;
			}

			protected override void OnParseComplete (OptionContext c)
			{
				action (
						Parse<TKey> (c.OptionValues [0], c),
						Parse<TValue> (c.OptionValues [1], c));
			}
		}

		public OptionSet Add<T> (string prototype, Action<T> action)
		{
			return Add (prototype, null, action);
		}

		public OptionSet Add<T> (string prototype, string description, Action<T> action)
		{
			return Add (new ActionOption<T> (prototype, description, action));
		}

		public OptionSet Add<TKey, TValue> (string prototype, OptionAction<TKey, TValue> action)
		{
			return Add (prototype, null, action);
		}

		public OptionSet Add<TKey, TValue> (string prototype, string description, OptionAction<TKey, TValue> action)
		{
			return Add (new ActionOption<TKey, TValue> (prototype, description, action));
		}

		public OptionSet Add (ArgumentSource source)
		{
			if (source == null)
				throw new ArgumentNullException ("source");
			sources.Add (source);
			return this;
		}

		protected virtual OptionContext CreateOptionContext ()
		{
			return new OptionContext (this);
		}

		public List<string> Parse (IEnumerable<string> arguments)
		{
			if (arguments == null)
				throw new ArgumentNullException ("arguments");
			OptionContext c = CreateOptionContext ();
			c.OptionIndex = -1;
			bool process = true;
			List<string> unprocessed = new List<string> ();
			Option def = Contains ("<>") ? this ["<>"] : null;
			ArgumentEnumerator ae = new ArgumentEnumerator (arguments);
			foreach (string argument in ae) {
				++c.OptionIndex;
				if (argument == "--") {
					process = false;
					continue;
				}
				if (!process) {
					Unprocessed (unprocessed, def, c, argument);
					continue;
				}
				if (AddSource (ae, argument))
					continue;
				if (!Parse (argument, c))
					Unprocessed (unprocessed, def, c, argument);
			}
			if (c.Option != null)
				c.Option.Invoke (c);
			return unprocessed;
		}

		class ArgumentEnumerator : IEnumerable<string> {
			List<IEnumerator<string>> sources = new List<IEnumerator<string>> ();

			public ArgumentEnumerator (IEnumerable<string> arguments)
			{
				sources.Add (arguments.GetEnumerator ());
			}

			public void Add (IEnumerable<string> arguments)
			{
				sources.Add (arguments.GetEnumerator ());
			}

			public IEnumerator<string> GetEnumerator ()
			{
				do {
					IEnumerator<string> c = sources [sources.Count-1];
					if (c.MoveNext ())
						yield return c.Current;
					else {
						c.Dispose ();
						sources.RemoveAt (sources.Count-1);
					}
				} while (sources.Count > 0);
			}

			IEnumerator IEnumerable.GetEnumerator ()
			{
				return GetEnumerator ();
			}
		}

		bool AddSource (ArgumentEnumerator ae, string argument)
		{
			foreach (ArgumentSource source in sources) {
				IEnumerable<string> replacement;
				if (!source.GetArguments (argument, out replacement))
					continue;
				ae.Add (replacement);
				return true;
			}
			return false;
		}

		private static bool Unprocessed (ICollection<string> extra, Option def, OptionContext c, string argument)
		{
			if (def == null) {
				extra.Add (argument);
				return false;
			}
			c.OptionValues.Add (argument);
			c.Option = def;
			c.Option.Invoke (c);
			return false;
		}

		private readonly Regex ValueOption = new Regex (
			@"^(?<flag>--|-|/)(?<name>[^:=]+)((?<sep>[:=])(?<value>.*))?$");

		protected bool GetOptionParts (string argument, out string flag, out string name, out string sep, out string value)
		{
			if (argument == null)
				throw new ArgumentNullException ("argument");

			flag = name = sep = value = null;
			Match m = ValueOption.Match (argument);
			if (!m.Success) {
				return false;
			}
			flag  = m.Groups ["flag"].Value;
			name  = m.Groups ["name"].Value;
			if (m.Groups ["sep"].Success && m.Groups ["value"].Success) {
				sep   = m.Groups ["sep"].Value;
				value = m.Groups ["value"].Value;
			}
			return true;
		}

		protected virtual bool Parse (string argument, OptionContext c)
		{
			if (c.Option != null) {
				ParseValue (argument, c);
				return true;
			}

			string f, n, s, v;
			if (!GetOptionParts (argument, out f, out n, out s, out v))
				return false;

			Option p;
			if (Contains (n)) {
				p = this [n];
				c.OptionName = f + n;
				c.Option     = p;
				switch (p.OptionValueType) {
					case OptionValueType.None:
						c.OptionValues.Add (n);
						c.Option.Invoke (c);
						break;
					case OptionValueType.Optional:
					case OptionValueType.Required: 
						ParseValue (v, c);
						break;
				}
				return true;
			}
			// no match; is it a bool option?
			if (ParseBool (argument, n, c))
				return true;
			// is it a bundled option?
			if (ParseBundledValue (f, string.Concat (n + s + v), c))
				return true;

			return false;
		}

		private void ParseValue (string option, OptionContext c)
		{
			if (option != null)
				foreach (string o in c.Option.ValueSeparators != null 
						? option.Split (c.Option.ValueSeparators, c.Option.MaxValueCount - c.OptionValues.Count, StringSplitOptions.None)
						: new string[]{option}) {
					c.OptionValues.Add (o);
				}
			if (c.OptionValues.Count == c.Option.MaxValueCount || 
					c.Option.OptionValueType == OptionValueType.Optional)
				c.Option.Invoke (c);
			else if (c.OptionValues.Count > c.Option.MaxValueCount) {
				throw new OptionException (localizer (string.Format (
								"Error: Found {0} option values when expecting {1}.", 
								c.OptionValues.Count, c.Option.MaxValueCount)),
						c.OptionName);
			}
		}

		private bool ParseBool (string option, string n, OptionContext c)
		{
			Option p;
			string rn;
			if (n.Length >= 1 && (n [n.Length-1] == '+' || n [n.Length-1] == '-') &&
					Contains ((rn = n.Substring (0, n.Length-1)))) {
				p = this [rn];
				string v = n [n.Length-1] == '+' ? option : null;
				c.OptionName  = option;
				c.Option      = p;
				c.OptionValues.Add (v);
				p.Invoke (c);
				return true;
			}
			return false;
		}

		private bool ParseBundledValue (string f, string n, OptionContext c)
		{
			if (f != "-")
				return false;
			for (int i = 0; i < n.Length; ++i) {
				Option p;
				string opt = f + n [i].ToString ();
				string rn = n [i].ToString ();
				if (!Contains (rn)) {
					if (i == 0)
						return false;
					throw new OptionException (string.Format (localizer (
									"Cannot use unregistered option '{0}' in bundle '{1}'."), rn, f + n), null);
				}
				p = this [rn];
				switch (p.OptionValueType) {
					case OptionValueType.None:
						Invoke (c, opt, n, p);
						break;
					case OptionValueType.Optional:
					case OptionValueType.Required: {
						string v     = n.Substring (i+1);
						c.Option     = p;
						c.OptionName = opt;
						ParseValue (v.Length != 0 ? v : null, c);
						return true;
					}
					default:
						throw new InvalidOperationException ("Unknown OptionValueType: " + p.OptionValueType);
				}
			}
			return true;
		}

		private static void Invoke (OptionContext c, string name, string value, Option option)
		{
			c.OptionName  = name;
			c.Option      = option;
			c.OptionValues.Add (value);
			option.Invoke (c);
		}

		private const int OptionWidth = 29;
		private const int Description_FirstWidth  = 80 - OptionWidth;
		private const int Description_RemWidth    = 80 - OptionWidth - 2;

		static  readonly    string      CommandHelpIndentStart       = new string (' ', OptionWidth);
		static  readonly    string      CommandHelpIndentRemaining   = new string (' ', OptionWidth + 2);

		public void WriteOptionDescriptions (TextWriter o)
		{
			foreach (Option p in this) {
				int written = 0;

				if (p.Hidden)
					continue;

				Category c = p as Category;
				if (c != null) {
					WriteDescription (o, p.Description, "", 80, 80);
					continue;
				}
				CommandOption co = p as CommandOption;
				if (co != null) {
					WriteCommandDescription (o, co.Command, co.CommandName);
					continue;
				}

				if (!WriteOptionPrototype (o, p, ref written))
					continue;

				if (written < OptionWidth)
					o.Write (new string (' ', OptionWidth - written));
				else {
					o.WriteLine ();
					o.Write (new string (' ', OptionWidth));
				}

				WriteDescription (o, p.Description, new string (' ', OptionWidth+2),
						Description_FirstWidth, Description_RemWidth);
			}

			foreach (ArgumentSource s in sources) {
				string[] names = s.GetNames ();
				if (names == null || names.Length == 0)
					continue;

				int written = 0;

				Write (o, ref written, "  ");
				Write (o, ref written, names [0]);
				for (int i = 1; i < names.Length; ++i) {
					Write (o, ref written, ", ");
					Write (o, ref written, names [i]);
				}

				if (written < OptionWidth)
					o.Write (new string (' ', OptionWidth - written));
				else {
					o.WriteLine ();
					o.Write (new string (' ', OptionWidth));
				}

				WriteDescription (o, s.Description, new string (' ', OptionWidth+2),
						Description_FirstWidth, Description_RemWidth);
			}
		}

		internal void WriteCommandDescription (TextWriter o, Command c, string commandName)
		{
			var name = new string (' ', 8) + (commandName ?? c.Name);
			if (name.Length < OptionWidth - 1) {
				WriteDescription (o, name + new string (' ', OptionWidth - name.Length) + c.Help, CommandHelpIndentRemaining, 80, Description_RemWidth);
			} else {
				WriteDescription (o, name, "", 80, 80);
				WriteDescription (o, CommandHelpIndentStart + c.Help, CommandHelpIndentRemaining, 80, Description_RemWidth);
			}
		}

		void WriteDescription (TextWriter o, string value, string prefix, int firstWidth, int remWidth)
		{
			bool indent = false;
			foreach (string line in GetLines (localizer (GetDescription (value)), firstWidth, remWidth)) {
				if (indent)
					o.Write (prefix);
				o.WriteLine (line);
				indent = true;
			}
		}

		bool WriteOptionPrototype (TextWriter o, Option p, ref int written)
		{
			string[] names = p.Names;

			int i = GetNextOptionIndex (names, 0);
			if (i == names.Length)
				return false;

			if (names [i].Length == 1) {
				Write (o, ref written, "  -");
				Write (o, ref written, names [0]);
			}
			else {
				Write (o, ref written, "      --");
				Write (o, ref written, names [0]);
			}

			for ( i = GetNextOptionIndex (names, i+1); 
					i < names.Length; i = GetNextOptionIndex (names, i+1)) {
				Write (o, ref written, ", ");
				Write (o, ref written, names [i].Length == 1 ? "-" : "--");
				Write (o, ref written, names [i]);
			}

			if (p.OptionValueType == OptionValueType.Optional ||
					p.OptionValueType == OptionValueType.Required) {
				if (p.OptionValueType == OptionValueType.Optional) {
					Write (o, ref written, localizer ("["));
				}
				Write (o, ref written, localizer ("=" + GetArgumentName (0, p.MaxValueCount, p.Description)));
				string sep = p.ValueSeparators != null && p.ValueSeparators.Length > 0 
					? p.ValueSeparators [0]
					: " ";
				for (int c = 1; c < p.MaxValueCount; ++c) {
					Write (o, ref written, localizer (sep + GetArgumentName (c, p.MaxValueCount, p.Description)));
				}
				if (p.OptionValueType == OptionValueType.Optional) {
					Write (o, ref written, localizer ("]"));
				}
			}
			return true;
		}

		static int GetNextOptionIndex (string[] names, int i)
		{
			while (i < names.Length && names [i] == "<>") {
				++i;
			}
			return i;
		}

		static void Write (TextWriter o, ref int n, string s)
		{
			n += s.Length;
			o.Write (s);
		}

		static string GetArgumentName (int index, int maxIndex, string description)
		{
			var matches = Regex.Matches (description ?? "", @"(?<=(?<!\{)\{)[^{}]*(?=\}(?!\}))"); // ignore double braces 
			string argName = "";
			foreach (Match match in matches) {
				var parts = match.Value.Split (':');
				// for maxIndex=1 it can be {foo} or {0:foo}
				if (maxIndex == 1) {
					argName = parts[parts.Length - 1];
				}
				// look for {i:foo} if maxIndex > 1
				if (maxIndex > 1 && parts.Length == 2 && 
					parts[0] == index.ToString (CultureInfo.InvariantCulture)) {
					argName = parts[1];
				}
			}

			if (string.IsNullOrEmpty (argName)) {
				argName = maxIndex == 1 ? "VALUE" : "VALUE" + (index + 1);
			}
			return argName;
		}

		private static string GetDescription (string description)
		{
			if (description == null)
				return string.Empty;
			StringBuilder sb = new StringBuilder (description.Length);
			int start = -1;
			for (int i = 0; i < description.Length; ++i) {
				switch (description [i]) {
					case '{':
						if (i == start) {
							sb.Append ('{');
							start = -1;
						}
						else if (start < 0)
							start = i + 1;
						break;
					case '}':
						if (start < 0) {
							if ((i+1) == description.Length || description [i+1] != '}')
								throw new InvalidOperationException ("Invalid option description: " + description);
							++i;
							sb.Append ("}");
						}
						else {
							sb.Append (description.Substring (start, i - start));
							start = -1;
						}
						break;
					case ':':
						if (start < 0)
							goto default;
						start = i + 1;
						break;
					default:
						if (start < 0)
							sb.Append (description [i]);
						break;
				}
			}
			return sb.ToString ();
		}

		private static IEnumerable<string> GetLines (string description, int firstWidth, int remWidth)
		{
			return StringCoda.WrappedLines (description, firstWidth, remWidth);
		}
	}

	public class Command
	{
		public      string                              Name            {get;}
		public      string                              Help            {get;}

		public      OptionSet                           Options         {get; set;}
		public      Action<IEnumerable<string>>         Run             {get; set;}

		public      CommandSet                          CommandSet      {get; internal set;}

		public Command (string name, string help = null)
		{
			if (string.IsNullOrEmpty (name))
				throw new ArgumentNullException (nameof (name));

			Name    = NormalizeCommandName (name);
			Help    = help;
		}

		static string NormalizeCommandName (string name)
		{
			var value = new StringBuilder (name.Length);
			var space = false;
			for (int i = 0; i < name.Length; ++i) {
				if (!char.IsWhiteSpace (name, i)) {
					space   = false;
					value.Append (name [i]);
				}
				else if (!space) {
					space   = true;
					value.Append (' ');
				}
			}
			return value.ToString ();
		}

		public virtual int Invoke (IEnumerable<string> arguments)
		{
			var rest    = Options?.Parse (arguments) ?? arguments;
			Run?.Invoke (rest);
			return 0;
		}
	}

	class CommandOption : Option
	{
		public      Command             Command         {get;}
		public      string              CommandName     {get;}

		// Prototype starts with '=' because this is an invalid prototype
		// (see Option.ParsePrototype(), and thus it'll prevent Category
		// instances from being accidentally used as normal options.
		public CommandOption (Command command, string commandName = null, bool hidden = false)
			: base ("=:Command:= " + (commandName ?? command?.Name), (commandName ?? command?.Name), maxValueCount: 0, hidden: hidden)
		{
			if (command == null)
				throw new ArgumentNullException (nameof (command));
			Command = command;
			CommandName = commandName ?? command.Name;
		}

		protected override void OnParseComplete (OptionContext c)
		{
			throw new NotSupportedException ("CommandOption.OnParseComplete should not be invoked.");
		}
	}

	class HelpOption : Option
	{
		Option      option;
		CommandSet  commands;

		public HelpOption (CommandSet commands, Option d)
			: base (d.Prototype, d.Description, d.MaxValueCount, d.Hidden)
		{
			this.commands   = commands;
			this.option     = d;
		}

		protected override void OnParseComplete (OptionContext c)
		{
			commands.showHelp  = true;

			option?.InvokeOnParseComplete (c);
		}
	}

	class CommandOptionSet : OptionSet
	{
		CommandSet  commands;

		public CommandOptionSet (CommandSet commands, MessageLocalizerConverter localizer)
			: base (localizer)
		{
			this.commands = commands;
		}

		protected override void SetItem (int index, Option item)
		{
			if (ShouldWrapOption (item)) {
				base.SetItem (index, new HelpOption (commands, item));
				return;
			}
			base.SetItem (index, item);
		}

		bool ShouldWrapOption (Option item)
		{
			if (item == null)
				return false;
			var help = item as HelpOption;
			if (help != null)
				return false;
			foreach (var n in item.Names) {
				if (n == "help")
					return true;
			}
			return false;
		}

		protected override void InsertItem (int index, Option item)
		{
			if (ShouldWrapOption (item)) {
				base.InsertItem (index, new HelpOption (commands, item));
				return;
			}
			base.InsertItem (index, item);
		}
	}

	public class CommandSet : KeyedCollection<string, Command>
	{
		readonly    string          suite;

		OptionSet                   options;
		TextWriter                  outWriter;
		TextWriter                  errorWriter;

		internal    List<CommandSet>        NestedCommandSets;

		internal    HelpCommand     help;

		internal    bool            showHelp;

		internal    OptionSet       Options     => options;

#if !PCL || NETSTANDARD1_3
		public CommandSet(string suite, MessageLocalizerConverter localizer = null)
			: this(suite, Console.Out, Console.Error, localizer)
		{
		}
#endif
		
		public CommandSet (string suite, TextWriter output, TextWriter error, MessageLocalizerConverter localizer = null)
		{
			if (suite == null)
				throw new ArgumentNullException (nameof (suite));
			if (output == null)
				throw new ArgumentNullException (nameof (output));
			if (error == null)
				throw new ArgumentNullException (nameof (error));

			this.suite  = suite;
			options     = new CommandOptionSet (this, localizer);
			outWriter   = output;
			errorWriter = error;
		}

		public  string                          Suite               => suite;
		public  TextWriter                      Out                 => outWriter;
		public  TextWriter                      Error               => errorWriter;
		public  MessageLocalizerConverter       MessageLocalizer    => options.MessageLocalizer;

		protected override string GetKeyForItem (Command item)
		{
			return item?.Name;
		}

		public new CommandSet Add (Command value)
		{
			if (value == null)
				throw new ArgumentNullException (nameof (value));
			AddCommand (value);
			options.Add (new CommandOption (value));
			return this;
		}

		void AddCommand (Command value)
		{
			if (value.CommandSet != null && value.CommandSet != this) {
				throw new ArgumentException ("Command instances can only be added to a single CommandSet.", nameof (value));
			}
			value.CommandSet                = this;
			if (value.Options != null) {
				value.Options.MessageLocalizer  = options.MessageLocalizer;
			}

			base.Add (value);

			help    = help ?? value as HelpCommand;
		}

		public CommandSet Add (string header)
		{
			options.Add (header);
			return this;
		}

		public CommandSet Add (Option option)
		{
			options.Add (option);
			return this;
		}

		public CommandSet Add (string prototype, Action<string> action)
		{
			options.Add (prototype, action);
			return this;
		}

		public CommandSet Add (string prototype, string description, Action<string> action)
		{
			options.Add (prototype, description, action);
			return this;
		}

		public CommandSet Add (string prototype, string description, Action<string> action, bool hidden)
		{
			options.Add (prototype, description, action, hidden);
			return this;
		}

		public CommandSet Add (string prototype, OptionAction<string, string> action)
		{
			options.Add (prototype, action);
			return this;
		}

		public CommandSet Add (string prototype, string description, OptionAction<string, string> action)
		{
			options.Add (prototype, description, action);
			return this;
		}

		public CommandSet Add (string prototype, string description, OptionAction<string, string> action, bool hidden)
		{
			options.Add (prototype, description, action, hidden);
			return this;
		}

		public CommandSet Add<T> (string prototype, Action<T> action)
		{
			options.Add (prototype, null, action);
			return this;
		}

		public CommandSet Add<T> (string prototype, string description, Action<T> action)
		{
			options.Add (prototype, description, action);
			return this;
		}

		public CommandSet Add<TKey, TValue> (string prototype, OptionAction<TKey, TValue> action)
		{
			options.Add (prototype, action);
			return this;
		}

		public CommandSet Add<TKey, TValue> (string prototype, string description, OptionAction<TKey, TValue> action)
		{
			options.Add (prototype, description, action);
			return this;
		}

		public CommandSet Add (ArgumentSource source)
		{
			options.Add (source);
			return this;
		}

		public CommandSet Add (CommandSet nestedCommands)
		{
			if (nestedCommands == null)
				throw new ArgumentNullException (nameof (nestedCommands));

			if (NestedCommandSets == null) {
				NestedCommandSets   = new List<CommandSet> ();
			}

			if (!AlreadyAdded (nestedCommands)) {
				NestedCommandSets.Add (nestedCommands);
				foreach (var o in nestedCommands.options) {
					if (o is CommandOption c) {
						options.Add (new CommandOption (c.Command, $"{nestedCommands.Suite} {c.CommandName}"));
					}
					else {
						options.Add (o);
					}
				}
			}

			nestedCommands.options      = this.options;
			nestedCommands.outWriter    = this.outWriter;
			nestedCommands.errorWriter  = this.errorWriter;

			return this;
		}

		bool AlreadyAdded (CommandSet value)
		{
			if (value == this)
				return true;
			if (NestedCommandSets == null)
				return false;
			foreach (var nc in NestedCommandSets) {
				if (nc.AlreadyAdded (value))
					return true;
			}
			return false;
		}

		public IEnumerable<string> GetCompletions (string prefix = null)
		{
			string rest;
			ExtractToken (ref prefix, out rest);

			foreach (var command in this) {
				if (command.Name.StartsWith (prefix, StringComparison.OrdinalIgnoreCase)) {
					yield return command.Name;
				}
			}

			if (NestedCommandSets == null)
				yield break;

			foreach (var subset in NestedCommandSets) {
				if (subset.Suite.StartsWith (prefix, StringComparison.OrdinalIgnoreCase)) {
					foreach (var c in subset.GetCompletions (rest)) {
						yield return $"{subset.Suite} {c}";
					}
				}
			}
		}

		static void ExtractToken (ref string input, out string rest)
		{
			rest      = "";
			input     = input ?? "";

			int top   = input.Length;
			for (int i = 0; i < top; i++) {
				if (char.IsWhiteSpace (input [i]))
					continue;

				for (int j = i; j < top; j++) {
					if (char.IsWhiteSpace (input [j])) {
						rest  = input.Substring (j).Trim ();
						input = input.Substring (i, j).Trim ();
						return;
					}
				}
				rest  = "";
				if (i != 0)
					input = input.Substring (i).Trim ();
				return;
			}
		}

		public int Run (IEnumerable<string> arguments)
		{
			if (arguments == null)
				throw new ArgumentNullException (nameof (arguments));

			this.showHelp   = false;
			if (help == null) {
				help    = new HelpCommand ();
				AddCommand (help);
			}
			Action<string>  setHelp     = v => showHelp = v != null;
			if (!options.Contains ("help")) {
				options.Add ("help", "", setHelp, hidden: true);
			}
			if (!options.Contains ("?")) {
				options.Add ("?", "", setHelp, hidden: true);
			}
			var extra   = options.Parse (arguments);
			if (extra.Count == 0) {
				if (showHelp) {
					return help.Invoke (extra);
				}
				Out.WriteLine (options.MessageLocalizer ($"Use `{Suite} help` for usage."));
				return 1;
			}
			var command = GetCommand (extra);
			if (command == null) {
				help.WriteUnknownCommand (extra [0]);
				return 1;
			}
			if (showHelp) {
				if (command.Options?.Contains ("help") ?? true) {
					extra.Add ("--help");
					return command.Invoke (extra);
				}
				command.Options.WriteOptionDescriptions (Out);
				return 0;
			}
			return command.Invoke (extra);
		}

		internal Command GetCommand (List<string> extra)
		{
			return TryGetLocalCommand (extra) ?? TryGetNestedCommand (extra);
		}

		Command TryGetLocalCommand (List<string> extra)
		{
			var name    = extra [0];
			if (Contains (name)) {
				extra.RemoveAt (0);
				return this [name];
			}
			for (int i = 1; i < extra.Count; ++i) {
				name = name + " " + extra [i];
				if (!Contains (name))
					continue;
				extra.RemoveRange (0, i+1);
				return this [name];
			}
			return null;
		}

		Command TryGetNestedCommand (List<string> extra)
		{
			if (NestedCommandSets == null)
				return null;

			var nestedCommands	= NestedCommandSets.Find (c => c.Suite == extra [0]);
			if (nestedCommands == null)
				return null;

			var extraCopy = new List<string> (extra);
			extraCopy.RemoveAt (0);
			if (extraCopy.Count == 0)
				return null;

			var command = nestedCommands.GetCommand (extraCopy);
			if (command != null) {
				extra.Clear ();
				extra.AddRange (extraCopy);
				return command;
			}
			return null;
		}
	}

	public class HelpCommand : Command
	{
		public HelpCommand ()
			: base ("help", help: "Show this message and exit")
		{
		}

		public override int Invoke (IEnumerable<string> arguments)
		{
			var extra   = new List<string> (arguments ?? new string [0]);
			var _       = CommandSet.Options.MessageLocalizer;
			if (extra.Count == 0) {
				CommandSet.Options.WriteOptionDescriptions (CommandSet.Out);
				return 0;
			}
			var command = CommandSet.GetCommand (extra);
			if (command == this || extra.Contains ("--help")) {
				CommandSet.Out.WriteLine (_ ($"Usage: {CommandSet.Suite} COMMAND [OPTIONS]"));
				CommandSet.Out.WriteLine (_ ($"Use `{CommandSet.Suite} help COMMAND` for help on a specific command."));
				CommandSet.Out.WriteLine ();
				CommandSet.Out.WriteLine (_ ($"Available commands:"));
				CommandSet.Out.WriteLine ();
				var commands    = GetCommands ();
				commands.Sort ((x, y) => string.Compare (x.Key, y.Key, StringComparison.OrdinalIgnoreCase));
				foreach (var c in commands) {
					if (c.Key == "help") {
						continue;
					}
					CommandSet.Options.WriteCommandDescription (CommandSet.Out, c.Value, c.Key);
				}
				CommandSet.Options.WriteCommandDescription (CommandSet.Out, CommandSet.help, "help");
				return 0;
			}
			if (command == null) {
				WriteUnknownCommand (extra [0]);
				return 1;
			}
			if (command.Options != null) {
				command.Options.WriteOptionDescriptions (CommandSet.Out);
				return 0;
			}
			return command.Invoke (new [] { "--help" });
		}

		List<KeyValuePair<string, Command>> GetCommands ()
		{
			var commands    = new List<KeyValuePair<string, Command>> ();

			foreach (var c in CommandSet) {
				commands.Add (new KeyValuePair<string, Command>(c.Name, c));
			}

			if (CommandSet.NestedCommandSets == null)
				return commands;

			foreach (var nc in CommandSet.NestedCommandSets) {
				AddNestedCommands (commands, "", nc);
			}

			return commands;
		}

		void AddNestedCommands (List<KeyValuePair<string, Command>> commands, string outer, CommandSet value)
		{
			foreach (var v in value) {
				commands.Add (new KeyValuePair<string, Command>($"{outer}{value.Suite} {v.Name}", v));
			}
			if (value.NestedCommandSets == null)
				return;
			foreach (var nc in value.NestedCommandSets) {
				AddNestedCommands (commands, $"{outer}{value.Suite} ", nc);
			}
		}

		internal void WriteUnknownCommand (string unknownCommand)
		{
			CommandSet.Error.WriteLine (CommandSet.Options.MessageLocalizer ($"{CommandSet.Suite}: Unknown command: {unknownCommand}"));
			CommandSet.Error.WriteLine (CommandSet.Options.MessageLocalizer ($"{CommandSet.Suite}: Use `{CommandSet.Suite} help` for usage."));
		}
	}
}

