Command line argument parser

Command-line-argument-parser.cs

static void Main(string[] args)
{
	string[] example = { @"--arg1=""test"" --arg2= this is wrong --arg3=x --arg4=""value 4""" };
	// Default usage
	CommandLineTokenizer tokenizer = new CommandLineTokenizer(example);
	Console.WriteLine(tokenizer["arg1"]);
	Console.WriteLine(tokenizer["arg2"]); // bad tokens are blank strings
	Console.WriteLine(tokenizer["arg5"]); // unknown tokens will also be blank string
	// Alternative usage
	tokenizer = new CommandLineTokenizer();
	List<KeyValuePair<string, string>> list = tokenizer.Tokenize(example);
}

public class CommandLineTokenizer
{
	private enum State
	{
		None,
		FirstDash,
		SecondDash,
		StartArg,
		StartArgDoubleQuotes,
		EndArgDoubleQuotes,
		StartArgSingleQuotes,
		EndArgSingleQuotes,
		Parse
	}

	private List<KeyValuePair<string, string>> _tokens;

	public string this[string key]
	{
		get
		{
			for (int i = 0; i < _tokens.Count; i++)
			{
				if (_tokens[i].Key == key)
					return _tokens[i].Value;
			}
			return "";
		}
	}

	public CommandLineTokenizer()
	{
		string line = Environment.CommandLine;
		line = line.Replace("\"" + Process.GetCurrentProcess().MainModule.FileName + "\"", "");
		_tokens = Tokenize(line);
	}

	public CommandLineTokenizer(string[] args)
		: this()
	{
		string input = string.Join(" ", args);
		_tokens = Tokenize(input);
	}

	public List<KeyValuePair<string, string>> Tokenize(string input)
	{
		return Pass2(Pass1(input));
	}

	private List<string> Pass1(string input)
	{
		State state = State.None;
		int start = 0;
		int end = 0;
		List<string> list = new List<string>();
		for (int i = 0; i < input.Length; i++)
		{
			char current = input[i];
			//Console.WriteLine("{0} {1}", current, state);
			if (input[i] == '-')
			{
				if (state == State.None)
				{
					state = State.FirstDash;
				}
				else if (state == State.FirstDash)
				{
					state = State.SecondDash;
				}
				else if (state == State.SecondDash)
				{
					state = State.None;
					start = 0;
				}
			}
			else if (state == State.SecondDash)
			{
				start = i;
				state = State.StartArg;
			}
			else if (current == '"')
			{
				if (state == State.StartArg)
				{
					state = State.StartArgDoubleQuotes;
				}
				else if (state == State.StartArgDoubleQuotes)
				{
					state = State.EndArgDoubleQuotes;
					if (i == input.Length - 1)
					{
						state = State.Parse;
						end = input.Length;
					}
				}
			}
			else if (current == '\'')
			{
				if (state == State.StartArg)
				{
					state = State.StartArgSingleQuotes;
				}
				else if (state == State.StartArgSingleQuotes)
				{
					state = State.EndArgSingleQuotes;
					if (i == input.Length - 1)
					{
						state = State.Parse;
						end = input.Length;
					}
				}
			}
			else if ((state == State.EndArgSingleQuotes || state == State.EndArgDoubleQuotes) && (current == ' ' || i == input.Length - 1))
			{
				end = i + 1;
				state = State.Parse;
			}
			else if (state == State.StartArg && (current == ' ' || i == input.Length - 1))
			{
				end = i + 1; // get past this current char
				state = State.Parse;
			}
			if (state == State.Parse)
			{
				state = State.None;
				list.Add(input.Substring(start, end - start));
			}
		}
		return list;
	}

	private List<KeyValuePair<string, string>> Pass2(List<string> list)
	{
		List<KeyValuePair<string, string>> result = new List<KeyValuePair<string, string>>();
		foreach (string item in list)
		{
			int equals = item.IndexOf("=");
			if (equals > -1 && item.Length >= 3)
			{
				string key = item.Substring(0, equals);
				string value = item.Substring(equals + 1);
				KeyValuePair<string, string> pair = new KeyValuePair<string, string>(key, value);
				result.Add(pair);
			}
		}
		return result;
	}
}