NumbersOperatorsTokenizer.java

package com.abacus.evaluation.utils;

import com.abacus.evaluation.engine.TokenType;
import com.abacus.evaluation.model.Token;

import java.util.ArrayList;
import java.util.List;

public class NumbersOperatorsTokenizer {

    private NumbersOperatorsTokenizer() {
    }

    public static List<Token> tokenize(String input) {
        List<Token> res = new ArrayList<>();
        for (char ch : input.toCharArray()) {
            int tail = res.size() - 1;
            String current = String.valueOf(ch);
            if (ArithmeticUtils.isOperator(current) && !unaryOperator(current, tail, res)) {
                res.add(new Token(TokenType.OPERATOR, current));
            } else if (ArithmeticUtils.isStartBracket(current)) {
                res.add(new Token(TokenType.LEFT_BRACKET, current));
            } else if (ArithmeticUtils.isClosingBracket(current)) {
                res.add(new Token(TokenType.RIGHT_BRACKET, current));
            } else if (res.isEmpty() || unaryOperator(current, tail, res)) {
                res.add(new Token(TokenType.NUMBER, current));
            } else if (res.get(tail).getTokenType() != TokenType.NUMBER) {
                res.add(new Token(TokenType.NUMBER, current));
            } else {
                String number = res.remove(tail).getValue() + current;
                res.add(new Token(TokenType.NUMBER, number));
            }
        }
        return res;
    }

    private static boolean unaryOperator(String current, int tail, List<Token> res) {
        return ArithmeticUtils.isOperator(current) && (res.size() == 0 || res.get(tail).getTokenType() == TokenType.LEFT_BRACKET);
    }
}