package com.quantum.sql.parser;

import java.util.Vector;

/**
 * <p>An SQL Lexer.  From 
 * <a href="http://www.dictionary.com/">dictionary.com</a>:
 * 
 * <blockquote>
 * <p><b>lexer</b>
 *
 * <p>/lek'sr/ n. Common hacker shorthand for 'lexical
 * analyzer', the input-tokenizing stage in the parser for a language
 * (the part that breaks it into word-like pieces).
 * </blockquote>
 * 
 * <p>Note that this class has nothing to do with the Sci-fi channel's
 * <a href="http://www.scifi.com/lexx/">Lexx</a> TV series.
 */
public class SQLLexx {
	private static String endline = ";"; //$NON-NLS-1$
	private static String dash = "-"; //$NON-NLS-1$
	private static String group = "/"; //$NON-NLS-1$
	/**
	 * Parses a SQL text into tokens. 
	 * @param text
	 * @return a vector of Token objects.
	 */
	public static Vector parse(String text) {
		Vector tokens = new Vector();
		StringPointer p = new StringPointer(text);
		try {
			while (!p.isDone()) {
				int offset = p.getOffset();
				char c = p.getNext();
				// Adds END_OF_LINE token
				if (c == '\n') {
					tokens.addElement(new Token(Token.END_OF_LINE, "\n", offset, offset + 1));	
				}
				// Adds WHITESPACE token;
				else if (Character.isWhitespace(c)) {
					StringBuffer value = new StringBuffer();
					while (Character.isWhitespace(c) && !p.isDone()) {
						value.append(c);
						c = p.getNext();
					}
					// done because of is done
					if (Character.isWhitespace(c)) {
						value.append(c);
					} else if (!p.isDone()){
						p.back();
					}
					tokens.addElement(new Token(Token.WHITESPACE, value.toString(), offset, offset + value.length()));
				// Adds IDENTIFIER token (can be reserved SQL word or not);
				} else if (Character.isLetter(c) || c == '_' || c == '$') {
					StringBuffer value = new StringBuffer();
					while ((Character.isLetterOrDigit(c) || c == '_'  || c == '$') && !p.isDone()) {
						value.append(c);
						c = p.getNext();
					}
					if ((Character.isLetterOrDigit(c) || c == '_')) {
						value.append(c);
					} else if (!p.isDone()){
						p.back();
					}
					tokens.addElement(new Token(Token.IDENTIFIER, value.toString(), offset, offset + value.length()));
				// Adds LITERAL token;
				} else if (c == '\'') {
					StringBuffer value = new StringBuffer();
					value.append(c);
					if (!p.isDone()) {
						c = p.getNext();
						while (c != '\'' && c != '\n' && !p.isDone()) {
							value.append(c);
							c = p.getNext();
						}
						if (c == '\'' || p.isDone()) {
							value.append(c);
						} else if (!p.isDone()){
							p.back();
						}
					}
					tokens.addElement(new Token(Token.LITERAL, value.toString(), offset, offset + value.length()));
				// Adds COMMENT token (or SYMBOL (dash) if only one dash);
				} else if (c == '-') {
					p.mark();
					if (p.isDone()) {
						tokens.addElement(new Token(Token.SYMBOL, dash, offset, offset + 1));
					} else {
						char next = p.getNext();
						if (next == '-') {
							StringBuffer value = new StringBuffer("--"); //$NON-NLS-1$
							if (!p.isDone()) {
								c = p.getNext();
								while (c != '\n' && !p.isDone()) {
									value.append(c);
									c = p.getNext();
								}
								if (p.isDone()) {
									value.append(c);
								} else {
									p.back();
								}
							}
							tokens.addElement(new Token(Token.COMMENT, value.toString(), offset, offset + value.length()));
						} else {
							tokens.addElement(new Token(Token.SYMBOL, dash, offset, offset + 1));
							p.reset();
						}
					}
				// Adds SEPARATOR token (;),  considers the rest of the line as COMMENT token;
				} else if (c == ';') {
					tokens.addElement(new Token(Token.SEPARATOR, endline, offset, offset + 1));
					StringBuffer value = new StringBuffer();
					if (!p.isDone()) {
						c = p.getNext();
						while (c != '\n' && !p.isDone()) {
							value.append(c);
							c = p.getNext();
						}
						if (p.isDone()) {
							value.append(c);
						} else {
							p.back();
						}
						// We add to the offset so as to skip the initial ';'
						offset++;
						tokens.addElement(new Token(Token.COMMENT, value.toString(), offset, offset + value.length()));
					}
				// Adds NUMERIC token;
				} else if (Character.isDigit(c)) {
					StringBuffer value = new StringBuffer();
					while ((Character.isDigit(c) || c == '.') && !p.isDone()) {
						value.append(c);
						c = p.getNext();
					}
					if ((Character.isDigit(c) || c == '.')) {
						value.append(c);
					} else {
						p.back();
					}
					tokens.addElement(new Token(Token.NUMERIC, value.toString(), offset, offset + value.length()));
				// Adds COMMENT token (or GROUP (slash) if only one slash);
				} else if (c == '/') {
					p.mark();
					// If we have '/*', it's a comment till '*/' found or eof
					if (p.peek() == '*') {
						tokens.addElement(tokenizeComment(p, offset));
					} else {
						// It's not '/*' , so it's a group token
						// BCH ??? what's this business about groups?  
						// Shouldn't '/' be a divide operator?
						tokens.addElement(new Token(Token.SYMBOL, new String(new char[] {c}) /*group*/, offset, offset + 1));
						p.reset();
					}
				// Adds SYMBOL token;
				} else {
					tokens.addElement(new Token(Token.SYMBOL, new String(new char[] {c}), offset, offset + 1));
				}
			}
		} catch (RuntimeException e) {
			e.printStackTrace();
		}
		
//		System.out.println("-------------------");
//		for (int i = 0; i < tokens.size(); i++) {
//			System.out.println((Token) tokens.elementAt(i));
//		}
		return tokens;
	}
	/**
	 * @param tokens
	 * @param p
	 * @param offset
	 */
	private static Token tokenizeComment(StringPointer p, int offset) {
		char c;
		StringBuffer value = new StringBuffer();
		c = p.getNext();
		value.append('/');
		while (!( c == '*' && p.peek() == '/' ) && !p.isDone()) {
			value.append(c);
			c = p.getNext();
		}
		if (!p.isDone()){
			value.append(c);
			c = p.getNext();
			value.append(c);	
		}
		return new Token(Token.COMMENT, value.toString(), offset, offset + value.length());
	}
}