[自製腳本語言第三天]

public class Lexer {

	/**
	 * 註解
	 * group(2)
	 * 不放入queue
	 * 匹配註解 //.* : 匹配 //任意字 //.*
	 */
	public static String annot = "(//.*)";
	/**
	 * NumToken
	 * group(3) 小數點跟數字
	 */
	public static String num = "([0-9]+)";
	/** 
	 * StrToken
	 * group(4)
	 * 字符串 原始表達式 "(\\"|\\\\|\\n|[^*])*"
	 * \\\\\": 	 \\" 匹配 \" 
	 * \\\\\\\\: \\\\ 匹配 \\
	 * \\\\n: 	 \\n 匹配 \n
	 * [^\"]: 	 ^" 匹配所有不等於(")的字
	 */
	public static String str = "(\"(\\\\\"|\\\\\\\\|\\\\n|[^\"])*\")";
	/**
	 * 
	 * IdToken
	 * 標示符號
	 * [A-Z_a-z][A-Z_a-z0-9]*|==|<=|>=|&&|\|\||\p{punct}
	 */
	public static String id = "[A-Z_a-z][A-Z_a-z0-9]*|==|<=|>=|&&|\\|\\||\\p{Punct}";
	
	/**
	 * group(1)
	 */
	public static String g1 = "(" + annot +"|"+ num + "|" + str + "|" + id + ")?";
	/**
	 * 不放入queue
	 * \s*比對一個或多個 空白字元
	 */
	public static String regexPat = "\\s*" + g1 ;

	private Pattern pattern = Pattern.compile(regexPat);
	private List<Token> queue = new ArrayList<>();
	private boolean hasMore;
	private LineNumberReader reader;

	public Lexer(Reader r) {
		hasMore = true;
		reader = new LineNumberReader(r);
	}

	public Token read() throws ParseException {
		if (fillQueue(0))
			return queue.remove(0);
		else
			return Token.EOF;

	}

	public Token peek(int i) throws ParseException {
		if (fillQueue(i)) {
			return queue.get(i);
		} else
			return Token.EOF;
	}

	private boolean fillQueue(int i) throws ParseException {
		while (i >= queue.size())
			if (hasMore)
				readLine();
			else
				return false;
		return true;
	}

	private void readLine() throws ParseException {
		String line = null;
		try {
			line = reader.readLine();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		if (line == null) {
			hasMore = false;
			return;
		}
		int lineNo = reader.getLineNumber();
		Matcher matcher = pattern.matcher(line);
		matcher.useTransparentBounds(false);
		int pos = 0;
		int endPos = line.length();

		while (pos < endPos) {
			matcher.region(pos, endPos);
			if (matcher.lookingAt()) {
				addToken(lineNo, matcher);
				pos = matcher.end();
			} else {
				throw new ParseException("bad token at line " + lineNo, pos);
			}
			queue.add(new IdToken(lineNo, Token.EOL));
		}
	}

	private void addToken(int lineNo, Matcher matcher) {

		String m = matcher.group(1);
		if (m != null) // if not a space 
			if (matcher.group(2) == null) {// if not a comment 判斷是否為註解
				Token token;
				if (matcher.group(3) != null)
					token = new NumToken(lineNo, Integer.parseInt(m));
				else if (matcher.group(4) != null)
					token = new StrToken(lineNo, toStringLiteral(m));
				else
					token = new IdToken(lineNo, m);
				queue.add(token);
			}
	}

	private String toStringLiteral(String s) {
		StringBuilder sb = new StringBuilder();
		int len = s.length();
		for (int i = 1; i < len; i++) {
			char c = s.charAt(i);
			if (c == '\\' && i + 1 < len) {
				int c2 = s.charAt(i + 1);
				if (c2 == '"' || c2 == '\\')
					c = s.charAt(i++);
				else if (c2 == 'n') {
					++i;
					c = '\n';
				}
			}
			sb.append(c);
		}
		return sb.toString();

	}

	static class NumToken extends Token {
		private int value;

		public NumToken(int lineNo, int v) {
			super(lineNo);
			value = v;
		}

		public boolean isNumber() {
			return true;
		};

		public String getText() {
			return Integer.toString(value);
		}

		public int getNumber() {
			return value;
		}

	}

	static class IdToken extends Token {
		private String text;

		public IdToken(int i, String id) {
			super(i);
			text = id;
		}

		public boolean isIdentifier() {
			return true;
		}

		public String getText() {
			return text;
		}
	}

	static class StrToken extends Token {

		private String literal;

		public StrToken(int line, String Str) {
			super(line);
			literal = str;
		}

		public boolean isTring() {
			return true;
		}

		public String getText() {
			return literal;
		}
	}
}

}