using System;
using System.Collections.Generic;
using System.Text;

namespace Crayon
{
	internal static class Tokenizer
	{
		private static readonly HashSet<string> TWO_CHAR_TOKENS = new HashSet<string>("++ -- << >> == != <= >= && || += -= *= /= %= &= |= ^= **".Split(' '));
		private static readonly HashSet<char> IDENTIFIER_CHARS = new HashSet<char>("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_$".ToCharArray());
		private static readonly HashSet<char> WHITESPACE = new HashSet<char>(" \r\n\t".ToCharArray());

		public static TokenStream Tokenize(string filename, string code, int fileID, bool useMultiCharTokens)
		{
			code += '\n';
			code += '\0';

			int[] lineByIndex = new int[code.Length];
			int[] colByIndex = new int[code.Length];
			char c;
			int line = 0;
			int col = 0;
			for (int i = 0; i < code.Length; ++i)
			{
				c = code[i];
				lineByIndex[i] = line;
				colByIndex[i] = col;
				if (c == '\n')
				{
					++line;
					col = -1;
				}

				++col;
			}

			List<Token> tokens = new List<Token>();

			string commentType = null;
			string stringType = null;
			StringBuilder stringToken = null;
			string normalToken = null;
			int stringStart = 0;
			int normalStart = 0;

			bool previousIsWhitespace = false;
			bool tokenStartHasPreviousWhitespace = false;

			string c2;
			int length = code.Length;
			for (int i = 0; i < length; ++i)
			{
				c = code[i];
				c2 = (i >= (length - 1)) ? "" : ("" + c + code[i + 1]);

				if (c == '\0' && i == length - 1)
				{
					// Indicates the end of the stream. Throw an exception in cases where you left something lingering.
					if (commentType == "*") throw new Exception("Unclosed comment.");
					if (stringType != null) throw new Exception("Unclosed string.");
				}

				if (commentType == "/")
				{
					if (c == '\n')
					{
						commentType = null;
					}
					previousIsWhitespace = true;
				}
				else if (commentType == "*")
				{
					if (c2 == "*/")
					{
						commentType = null;
						++i;
					}
					previousIsWhitespace = true;
				}
				else if (stringType != null)
				{
					if (c == '\\')
					{
						stringToken.Append(c2);
						++i;
					}
					else if (c == stringType[0])
					{
						stringToken.Append(c);
						stringType = null;
						tokens.Add(new Token(stringToken.ToString(), fileID, filename, lineByIndex[stringStart], colByIndex[stringStart], tokenStartHasPreviousWhitespace));
					}
					else
					{
						stringToken.Append(c);
					}
					previousIsWhitespace = false;
				}
				else if (normalToken != null)
				{
					if (IDENTIFIER_CHARS.Contains(c))
					{
						normalToken += c;
					}
					else
					{
						tokens.Add(new Token(normalToken, fileID, filename, lineByIndex[normalStart], colByIndex[normalStart], tokenStartHasPreviousWhitespace));
						--i;
						normalToken = null;
					}
					previousIsWhitespace = false;
				}
				else if (useMultiCharTokens && TWO_CHAR_TOKENS.Contains(c2))
				{
					tokens.Add(new Token(c2, fileID, filename, lineByIndex[i], colByIndex[i], previousIsWhitespace));
					++i;
					previousIsWhitespace = false;
				}
				else if (WHITESPACE.Contains(c))
				{
					previousIsWhitespace = true;
				}
				else if (c == '"')
				{
					stringType = "\"";
					stringToken = new StringBuilder("" + stringType);
					stringStart = i;
					tokenStartHasPreviousWhitespace = previousIsWhitespace;
					previousIsWhitespace = false;
				}
				else if (c == '\'')
				{
					stringType = "'";
					stringToken = new StringBuilder("" + stringType);
					stringStart = i;
					tokenStartHasPreviousWhitespace = previousIsWhitespace;
					previousIsWhitespace = false;
				}
				else if (IDENTIFIER_CHARS.Contains(c))
				{
					normalToken = "" + c;
					normalStart = i;
					tokenStartHasPreviousWhitespace = previousIsWhitespace;
					previousIsWhitespace = false;
				}
				else if (c2 == "//")
				{
					commentType = "/";
					i += 1;
				}
				else if (c2 == "/*")
				{
					commentType = "*";
					i += 1;
				}
				else
				{
					tokens.Add(new Token("" + c, fileID, filename, lineByIndex[i], colByIndex[i], previousIsWhitespace));
					previousIsWhitespace = false;
				}
			}
			tokens.RemoveAt(tokens.Count - 1);
			return new TokenStream(tokens);
		}
	}
}
