Separates an identifier into its constituent parts

Identifier.cs

using System;
using System.Collections.Generic;
using NUnit.Framework;

namespace DevSearchTest
{
	class Identifier
	{
		public static string[] Separate(string rawId)
		{
			var id = (rawId ?? "").Trim ();
			if (id.Length == 0) return new string[0];			
			
			var idLower = id.ToLowerInvariant ();
			
			var parts = new List<string> ();
			
			var lastChar = ' ';
			
			var wordStart = 0;
			
			for (var i = 0; i < id.Length; i++) {
				var ch = id [i];
				var isSep = (ch=='_')||(ch=='-')||(ch==' ')||(ch=='\t');
				var newWord = isSep;
				if (!newWord && i > 0) {
					newWord = char.IsLower (lastChar) && char.IsUpper (ch);
					if (!newWord && char.IsUpper (lastChar) && char.IsUpper (ch) && (i + 1) < id.Length && char.IsLower (id[i+1])) {
						newWord = true;
					}
				}
				
				if (newWord) {
					if ((i - wordStart) > 0) {
						parts.Add (string.Intern (idLower.Substring (wordStart, i - wordStart)));
					}
					wordStart = isSep ? i + 1 : i;
				}
				
				lastChar = ch;
			}
			
			if (wordStart < id.Length) {
				parts.Add (string.Intern (idLower.Substring (wordStart)));
			}
			
			return parts.ToArray ();
		}
	}
	
	
	[TestFixture]
	public class Test
	{
		[Test]
		public void Empty ()
		{
			Assert.AreEqual (new string[0], Identifier.Separate (""));
			Assert.AreEqual (new string[0], Identifier.Separate (null));
			Assert.AreEqual (new string[0], Identifier.Separate (" "));
			Assert.AreEqual (new string[0], Identifier.Separate (" \r\n  \t "));
		}
		
		[Test]
		public void SingleWord ()
		{
			Assert.AreEqual (new string[]{"j35t3r"}, Identifier.Separate ("j35t3r"));
			Assert.AreEqual (new string[]{"j35t3r"}, Identifier.Separate ("J35T3R"));
			Assert.AreEqual (new string[]{"j35t3r"}, Identifier.Separate ("J35t3r"));
		}
		
		[Test]
		public void Underscores ()
		{			
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("this_is_long"));
			Assert.AreEqual (new string[]{"this","is","long","m"}, Identifier.Separate ("this_is_long_m"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("___this_is_long___"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("_this_is_long_"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("THIS_IS_Long"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("_THIS_IS_Long"));
			Assert.AreEqual (new string[]{"m","this","is","long"}, Identifier.Separate ("m_this_is_long"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("_this_is_long"));
			Assert.AreEqual (new string[]{"m","this","is","long","32"}, Identifier.Separate ("m_this_is_long_32"));
			Assert.AreEqual (new string[]{"m","this","is","long32"}, Identifier.Separate ("m_this_is_long32"));
		}
		
		[Test]
		public void Camel ()
		{
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("ThisIsLong"));
			Assert.AreEqual (new string[]{"m","this","is","long"}, Identifier.Separate ("m_ThisIsLong"));
			Assert.AreEqual (new string[]{"this","is","long"}, Identifier.Separate ("_ThisIsLong"));
			Assert.AreEqual (new string[]{"this","is","long","ext"}, Identifier.Separate ("ThisIsLongExt"));
			Assert.AreEqual (new string[]{"this","is","long","ext32"}, Identifier.Separate ("ThisIsLongExt32"));
		}
		
		[Test]
		public void HardCamel ()
		{
			Assert.AreEqual (new string[]{"html","element"}, Identifier.Separate ("HTMLElement"));
			Assert.AreEqual (new string[]{"html","element"}, Identifier.Separate ("HtmlElement"));			
			Assert.AreEqual (new string[]{"cg","context","eo","clip"}, Identifier.Separate ("CGContextEOClip"));
			Assert.AreEqual (new string[]{"cg","context","set","cmyk","fill","color"}, Identifier.Separate ("CGContextSetCMYKFillColor"));
			Assert.AreEqual (new string[]{"cg","context","translate","ctm"}, Identifier.Separate ("CGContextTranslateCTM"));
			Assert.AreEqual (new string[]{"cg","context","translate","ctm"}, Identifier.Separate ("CGContextTranslateCTM_"));
		}
		
		[Test]
		public void RubyIdentifiers ()
		{			
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("thisIsLong?"));
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("THIS_IS_Long?"));
			Assert.AreEqual (new string[]{"this","is","long!"}, Identifier.Separate ("_THIS_IS_Long!"));
		}
		
		[Test]
		public void Spaces ()
		{			
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("this Is Long?"));
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("THIS_IS   Long?"));
			Assert.AreEqual (new string[]{"th","is","is","long!"}, Identifier.Separate ("\t_TH  \t   IS_IS_Long!"));
		}
		
		[Test]
		public void LispIdentifiers ()
		{			
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("this-is-long?"));
			Assert.AreEqual (new string[]{"this","is","long?"}, Identifier.Separate ("THIS_IS_Long?"));
			Assert.AreEqual (new string[]{"this","is?","long!"}, Identifier.Separate ("_THIS-IS?-Long!"));
		}
	}
}