Create helper DiceRoller class

api/src/main/java/com/bartlomiejpluta/base/util/random/DiceRoller.java

@@ -0,0 +1,78 @@
+package com.bartlomiejpluta.base.util.random;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+import java.util.Optional;
+import java.util.Random;
+import java.util.regex.Pattern;
+
+import static java.lang.String.format;
+
+@Data
+@AllArgsConstructor
+public class DiceRoller {
+   private static final Pattern INT_PATTERN = Pattern.compile("[+-]?\\d+");
+   private static final Pattern CODE_PATTERN = Pattern.compile("(\\d+)d(\\d+)([+-]\\d+)?");
+   private final Random random = new Random();
+   private int rolls;
+   private int dice;
+   private int modifier;
+
+   public int roll() {
+      var sum = modifier;
+
+      for (int i = 0; i < rolls; ++i) {
+         sum += random.nextInt(dice) + 1;
+      }
+
+      return Math.max(0, sum);
+   }
+
+   public static DiceRoller of(String code) {
+      var intMatcher = INT_PATTERN.matcher(code);
+      if(intMatcher.matches()) {
+         return new DiceRoller(0, 0, Integer.parseInt(code));
+      }
+
+      var codeMatcher = CODE_PATTERN.matcher(code);
+      if(codeMatcher.matches()) {
+         var rolls = Integer.parseInt(codeMatcher.group(1));
+         var dice = Integer.parseInt(codeMatcher.group(2));
+         var modifier = Integer.parseInt(Optional.ofNullable(codeMatcher.group(3)).orElse("0"));
+         return new DiceRoller(rolls, dice, modifier);
+      }
+
+      throw new IllegalArgumentException("Argument is supposed to be in RPG dice code format (e.g. 2d4+2) or simple integer");
+   }
+
+   public int min() {
+      return Math.max(0, modifier + rolls);
+   }
+
+   public int max() {
+      return Math.max(0, modifier + rolls * dice);
+   }
+
+   public String code() {
+      var builder = new StringBuilder();
+      if(rolls > 0 && dice > 0) {
+         builder.append(format("%dd%d", rolls, dice));
+      }
+
+      if(!builder.isEmpty() && modifier != 0) {
+         builder
+                 .append(modifier > 0 ? "+" : "-")
+                 .append(Math.abs(modifier));
+      } else if(builder.isEmpty()) {
+         builder.append(modifier);
+      }
+
+      return builder.toString();
+   }
+
+   @Override
+   public String toString() {
+      return format("%s (min=%d, max=%d)", code(), min(), max());
+   }
+}