package com.aaront.exercise.basic.expr;
import java.util.ArrayList;
import java.util.List;
public class TokenParser {
public List<Token> parse(String expr) {
List<Token> tokens = new ArrayList<>();
int i = 0;
while (i < expr.length()) {
char c = expr.charAt(i);
if (isOperator(c)) {
Token t = new Token(Token.OPERATOR, String.valueOf(c));
tokens.add(t);
i++;
} else if (Character.isDigit(c)) {
int nextOperatorIndex = indexOfNextOperator(i, expr);
String value = expr.substring(i, nextOperatorIndex);
Token t = new Token(Token.NUMBER, value);
tokens.add(t);
i = nextOperatorIndex;
} else {
System.out.println("char :[" + c + "] is not number or operator,ignore");
i++;
}
}
return tokens;
}
private int indexOfNextOperator(int i, String expr) {
while (Character.isDigit(expr.charAt(i))) {
i++;
if (i == expr.length()) {
break;
}
}
return i;
}
private boolean isOperator(char c) {
String sc = String.valueOf(c);
return Token.OPERATORS.contains(sc);
}
}