import java.util.Iterator;

public class TokenString implements Iterable<Token> {
	
	private final String str;
	
	public TokenString(String str) {
		this.str = str;
	}
	
	public Iterator<Token> iterator() {
		return new TokenIterator(str);
	}
	
}

class TokenIterator implements Iterator<Token> {
	
	private static final char END = '\0';
	
	private final String str;
	private int pos;
	private Token next;
	
	public TokenIterator(String str) {
		this.str = str;
		next = advance();
	}
	
	public Token next() {
		Token tok = next;
		next = advance();
		return tok;
	}
	
	public boolean hasNext() {
		return next != null;
	}
	
	public void remove() {
		throw new UnsupportedOperationException();
	}
	
	private Token advance() {
		while ((pos < str.length()) && Character.isWhitespace(cur())) ++pos;
		char ch = cur();
		if (ch == END) return null;
		if (Character.isDigit(ch)) {
			int start = pos;
			++pos;
			while (Character.isDigit(cur())) ++pos;
			return Value.parse(str.substring(start, pos));
		}
		else if (Operator.isOperatorChar(ch)) {
			int start = pos;
			++pos;
			while (Operator.isOperatorChar(cur())) ++pos;
			return Operator.getBySymbol(str.substring(start, pos));
		}
		else if (NameToken.isNameStartChar(ch)) {
			int start = pos;
			++pos;
			while (NameToken.isNameChar(cur())) ++pos;
			return new NameToken(str.substring(start, pos));
		}
		else if (ch == '(') {
			++pos;
			return OpenParenthesisToken.INSTANCE;
		}
		else if (ch == ')') {
			++pos;
			return CloseParenthesisToken.INSTANCE;
		}
		else if (ch == ',') {
			++pos;
			return CommaToken.INSTANCE;
		}
		else {
			throw new IllegalArgumentException("illegal character " + ch + " at position " + pos + " in " + str);
		}
	}
	
	private char cur() {
		return charAt(pos);
	}
	
	private char charAt(int i) {
		if (i == str.length()) return END;
		else return str.charAt(i);
	}
	
}