package com.kabryxis.experienceeconomy;

import org.bukkit.entity.Player;

/**
 * A utility for managing Player experience properly.
 *
 * @author Jikoo
 */
public class Experience {

    /**
     * Calculates a player's total exp based on level and progress to next.
     * @see http://minecraft.gamepedia.com/Experience#Leveling_up
     *
     * @param player the Player
     *
     * @return the amount of exp the Player has
     */
    public static int getExp(Player player) {
        return getExpFromLevel(player.getLevel())
                + Math.round(getExpToNext(player.getLevel()) * player.getExp());
    }

    /**
     * Calculates total experience based on level.
     *
     * @see http://minecraft.gamepedia.com/Experience#Leveling_up
     *
     * "One can determine how much experience has been collected to reach a level using the equations:
     *
     *  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+)"
     *
     * @param level the level
     *
     * @return the total experience calculated
     */
    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;
    }

    /**
     * @see http://minecraft.gamepedia.com/Experience#Leveling_up
     *
     * "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;
    }

    /**
     * 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));
    }

    public static int getExpToNext(Player player) {
        return getExpFromLevel(player.getLevel() + 1) - getExp(player);
    }

}