ArithmeticOperators.java

package com.abacus.evaluation.engine;

import com.abacus.evaluation.model.Token;
import com.google.common.collect.ImmutableMap;
import org.apache.commons.lang3.tuple.Triple;

import java.util.Arrays;
import java.util.Map;

import static org.apache.commons.lang3.math.NumberUtils.toDouble;

public enum ArithmeticOperators {
    DIVISION("/", 1) {
        public double evaluate(double a, double b) {
            return a / b;
        }
    },
    MULTIPLICATION("*", 2) {
        public double evaluate(double a, double b) {
            return a * b;
        }
    },
    ADDITION("+", 3) {
        public double evaluate(double a, double b) {
            return a + b;
        }
    },
    SUBTRACTION("-", 3) {
        public double evaluate(double a, double b) {
            return a - b;
        }
    };

    public abstract double evaluate(double a, double b);

    private final String operator;
    private final int order;

    private static final Map<String, ArithmeticOperators> ALL_OPERATORS =
            Arrays.stream(ArithmeticOperators.values())
                    .collect(ImmutableMap.toImmutableMap(
                            op -> op.getOperator(),
                            op -> op
                    ));

    public static final Map<String, Integer> ALL_OPERATORS_WITH_PRECEDENCE =
            Arrays.stream(ArithmeticOperators.values())
                    .collect(ImmutableMap.toImmutableMap(
                            op -> op.getOperator(),
                            op -> op.getOrder()
                    ));

    ArithmeticOperators(String operator, int order) {
        this.operator = operator;
        this.order = order;
    }

    public String getOperator() {
        return operator;
    }

    public int getOrder() {
        return order;
    }

    public static Token evaluate(Triple<Token, Token, Token> inputs) {
        return new Token(TokenType.NUMBER,
                String.valueOf(ALL_OPERATORS.get(inputs.getMiddle().getValue()).evaluate(toDouble(inputs.getLeft().getValue()), toDouble(inputs.getRight().getValue())))
        );
    }
}