122 lines
3.8 KiB
Java
122 lines
3.8 KiB
Java
package world.bentobox.level.calculators;
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import java.text.ParseException;
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/**
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* Utility class to evaluate equations
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*/
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public class EquationEvaluator {
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private static class Parser {
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private final String input;
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private int pos = -1;
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private int currentChar;
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@SuppressWarnings("unused")
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private Parser() {
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throw new IllegalStateException("Utility class");
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}
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public Parser(String input) {
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this.input = input;
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moveToNextChar();
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}
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private void moveToNextChar() {
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currentChar = (++pos < input.length()) ? input.charAt(pos) : -1;
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}
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private boolean tryToEat(int charToEat) {
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while (currentChar == ' ') {
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moveToNextChar();
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}
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if (currentChar == charToEat) {
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moveToNextChar();
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return true;
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}
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return false;
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}
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public double evaluate() throws ParseException {
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double result = parseExpression();
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if (pos < input.length()) {
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throw new ParseException("Unexpected character: " + (char) currentChar, pos);
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}
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return result;
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}
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private double parseExpression() throws ParseException {
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double result = parseTerm();
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while (true) {
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if (tryToEat('+')) {
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result += parseTerm();
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} else if (tryToEat('-')) {
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result -= parseTerm();
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} else {
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return result;
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}
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}
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}
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private double parseFactor() throws ParseException {
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if (tryToEat('+')) {
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return parseFactor(); // unary plus
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}
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if (tryToEat('-')) {
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return -parseFactor(); // unary minus
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}
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double x;
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int startPos = this.pos;
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if (tryToEat('(')) { // parentheses
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x = parseExpression();
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tryToEat(')');
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} else if ((currentChar >= '0' && currentChar <= '9') || currentChar == '.') { // numbers
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while ((currentChar >= '0' && currentChar <= '9') || currentChar == '.') {
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moveToNextChar();
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}
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x = Double.parseDouble(input.substring(startPos, this.pos));
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} else if (currentChar >= 'a' && currentChar <= 'z') { // functions
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while (currentChar >= 'a' && currentChar <= 'z') {
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moveToNextChar();
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}
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String func = input.substring(startPos, this.pos);
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x = parseFactor();
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x = switch (func) {
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case "sqrt" -> Math.sqrt(x);
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case "sin" -> Math.sin(Math.toRadians(x));
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case "cos" -> Math.cos(Math.toRadians(x));
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case "tan" -> Math.tan(Math.toRadians(x));
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case "log" -> Math.log(x);
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default -> throw new ParseException("Unknown function: " + func, startPos);
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};
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} else {
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throw new ParseException("Unexpected: " + (char) currentChar, startPos);
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}
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if (tryToEat('^')) {
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x = Math.pow(x, parseFactor()); // exponentiation
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}
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return x;
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}
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private double parseTerm() throws ParseException {
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double x = parseFactor();
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for (;;) {
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if (tryToEat('*'))
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x *= parseFactor(); // multiplication
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else if (tryToEat('/'))
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x /= parseFactor(); // division
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else
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return x;
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}
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}
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}
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public static double eval(final String equation) throws ParseException {
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return new Parser(equation).evaluate();
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}
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}
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