XpUtils.java

package ru.cwcode.cwutils.xp;

import org.bukkit.Location;
import org.bukkit.entity.EntityType;
import org.bukkit.entity.ExperienceOrb;
import org.bukkit.entity.Player;

import java.util.Objects;

/**
 * A utility for managing Player experience properly.
 *
 * @author Jikoo
 */
public class XpUtils {
  public static void dropExp(final Location location, final int xp) {
    final ExperienceOrb orb = (ExperienceOrb) Objects.requireNonNull(location.getWorld()).spawnEntity(location, EntityType.EXPERIENCE_ORB);
    orb.setExperience(xp);
  }
  
  /**
   * Calculates a player's total exp based on level and progress to next.
   *
   * @param player the Player
   * @return the amount of exp the Player has
   * @see <a href="http://minecraft.gamepedia.com/Experience#Leveling_up">ref</a>
   */
  public static int getExp(Player player) {
    return getExpFromLevel(player.getLevel())
           + Math.round(getExpToNext(player.getLevel()) * player.getExp());
  }
  
  /**
   * Calculates total experience based on level.
   *
   * @param level the level
   * @return the total experience calculated
   * @see <a href="http://minecraft.gamepedia.com/Experience#Leveling_up">ref</a>
   * <p>
   * "One can determine how much experience has been collected to reach a level using the equations:
   * <p>
   * Total Experience = [Level]2 + 6[Level] (at levels 0-15)
   * 2.5[Level]2 - 40.5[Level] + 360 (at levels 16-30)
   * 4.5[Level]2 - 162.5[Level] + 2220 (at level 31+)"
   */
  public static int getExpFromLevel(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;
  }
  
  /**
   * Calculates level based on total experience.
   *
   * @param exp the total experience
   * @return the level calculated
   */
  public static double getLevelFromExp(long exp) {
    if (exp > 1395) {
      return (Math.sqrt(72 * exp - 54215) + 325) / 18;
    }
    if (exp > 315) {
      return Math.sqrt(40 * exp - 7839) / 10 + 8.1;
    }
    if (exp > 0) {
      return Math.sqrt(exp + 9) - 3;
    }
    return 0;
  }
  
  /**
   * Change a Player's exp.
   * <p>
   * This method should be used in place of {@link Player#giveExp(int)}, which does not properly
   * account for different levels requiring different amounts of experience.
   *
   * @param player the Player affected
   * @param exp    the amount of experience to add or remove
   */
  public static void changeExp(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));
  }
  
  /**
   * @see <a href="http://minecraft.gamepedia.com/Experience#Leveling_up">ref</a>
   * <p>
   * "The formulas for figuring out how many experience orbs you need to get to the next level are as follows:
   * Experience Required = 2[Current Level] + 7 (at levels 0-15)
   * 5[Current Level] - 38 (at levels 16-30)
   * 9[Current Level] - 158 (at level 31+)"
   */
  private static int getExpToNext(int level) {
    if (level > 30) {
      return 9 * level - 158;
    }
    if (level > 15) {
      return 5 * level - 38;
    }
    return 2 * level + 7;
  }
    
}