feat: ExperienceManager

src/main/java/in/arcadelabs/labaide/experience/ExperienceManager.java

@@ -0,0 +1,140 @@
+/*
+ *                LabAide - Common utility library for our products.
+ *                Copyright (C) 2022  ArcadeLabs Production.
+ *
+ *       This program is free software: you can redistribute it and/or modify
+ *       it under the terms of the GNU General Public License as published by
+ *       the Free Software Foundation, either version 3 of the License, or
+ *       (at your option) any later version.
+ *
+ *       This program is distributed in the hope that it will be useful,
+ *       but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *       GNU General Public License for more details.
+ *
+ *       You should have received a copy of the GNU General Public License
+ *       along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package in.arcadelabs.labaide.experience;
+
+import org.bukkit.entity.Player;
+
+/**
+ * Good job Mojang with messed up XP maths that I don't understand.
+ * Thanks to <a href="https://gist.github.com/Jikoo/30ec040443a4701b8980">Jikoo</a> for this utility class that made my life easier.
+ */
+public class ExperienceManager {
+  /**
+   * Calculate a player's total experience based on level and progress to next.
+   *
+   * @param player the Player
+   * @return the amount of experience the Player has
+   * @see <a href=http://minecraft.gamepedia.com/Experience#Leveling_up>Experience#Leveling_up</a>
+   */
+  public static int getExp(final Player player) {
+    return getExpFromLevel(player.getLevel())
+            + Math.round(getExpToNext(player.getLevel()) * player.getExp());
+  }
+
+  /**
+   * Calculate total experience based on level.
+   *
+   * @param level the level
+   * @return the total experience calculated
+   * @see <a href=http://minecraft.gamepedia.com/Experience#Leveling_up>Experience#Leveling_up</a>
+   */
+  public static int getExpFromLevel(final int level) {
+    if (level > 30) {
+      return (int) (4.5 * level * level - 162.5 * level + 2220);
+    }
+    if (level > 15) {
+      return (int) (2.5 * level * level - 40.5 * level + 360);
+    }
+    return level * level + 6 * level;
+  }
+
+  /**
+   * Calculate level (including progress to next level) based on total experience.
+   *
+   * @param exp the total experience
+   * @return the level calculated
+   */
+  public static double getLevelFromExp(final long exp) {
+    int level = getIntLevelFromExp(exp);
+
+    // Get remaining exp progressing towards next level. Cast to float for next bit of math.
+    float remainder = exp - (float) getExpFromLevel(level);
+
+    // Get level progress with float precision.
+    float progress = remainder / getExpToNext(level);
+
+    // Slap both numbers together and call it a day. While it shouldn't be possible for progress
+    // to be an invalid value (value < 0 || 1 <= value)
+    return ((double) level) + progress;
+  }
+
+  /**
+   * Calculate level based on total experience.
+   *
+   * @param exp the total experience
+   * @return the level calculated
+   */
+  public static int getIntLevelFromExp(final long exp) {
+    if (exp > 1395) {
+      return (int) ((Math.sqrt(72 * exp - 54215D) + 325) / 18);
+    }
+    if (exp > 315) {
+      return (int) (Math.sqrt(40 * exp - 7839D) / 10 + 8.1);
+    }
+    if (exp > 0) {
+      return (int) (Math.sqrt(exp + 9D) - 3);
+    }
+    return 0;
+  }
+
+  /**
+   * Get the total amount of experience required to progress to the next level.
+   *
+   * @param level the current level
+   * @see <a href=http://minecraft.gamepedia.com/Experience#Leveling_up>Experience#Leveling_up</a>
+   */
+  private static int getExpToNext(final int level) {
+    if (level >= 30) {
+      // Simplified formula. Internal: 112 + (level - 30) * 9
+      return level * 9 - 158;
+    }
+    if (level >= 15) {
+      // Simplified formula. Internal: 37 + (level - 15) * 5
+      return level * 5 - 38;
+    }
+    // Internal: 7 + level * 2
+    return level * 2 + 7;
+  }
+
+  /**
+   * Change a Player's experience.
+   *
+   * <p>This method is preferred over {@link Player#giveExp(int)}.
+   * <br>In older versions the method does not take differences in exp per level into account.
+   * This leads to overlevelling when granting players large amounts of experience.
+   * <br>In modern versions, while differing amounts of experience per level are accounted for, the
+   * approach used is loop-heavy and requires an excessive number of calculations, which makes it
+   * quite slow.
+   *
+   * @param player the Player affected
+   * @param exp    the amount of experience to add or remove
+   */
+  public static void changeExp(final Player player, int exp) {
+    exp += getExp(player);
+
+    if (exp < 0) {
+      exp = 0;
+    }
+
+    double levelAndExp = getLevelFromExp(exp);
+    int level = (int) levelAndExp;
+    player.setLevel(level);
+    player.setExp((float) (levelAndExp - level));
+  }
+}