BloodMagic/src/main/java/WayofTime/bloodmagic/item/ItemExperienceBook.java

package WayofTime.bloodmagic.item;

import WayofTime.bloodmagic.BloodMagic;
import WayofTime.bloodmagic.util.helper.NBTHelper;
import WayofTime.bloodmagic.client.IVariantProvider;
import WayofTime.bloodmagic.util.helper.TextHelper;
import net.minecraft.client.util.ITooltipFlag;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.init.SoundEvents;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.ActionResult;
import net.minecraft.util.EnumActionResult;
import net.minecraft.util.EnumHand;
import net.minecraft.world.World;
import net.minecraftforge.fml.relauncher.Side;
import net.minecraftforge.fml.relauncher.SideOnly;
import org.apache.commons.lang3.tuple.ImmutablePair;
import org.apache.commons.lang3.tuple.Pair;

import java.util.ArrayList;
import java.util.List;

public class ItemExperienceBook extends Item implements IVariantProvider {
    public ItemExperienceBook() {
        setUnlocalizedName(BloodMagic.MODID + ".experienceTome");
        setMaxStackSize(1);
        setCreativeTab(BloodMagic.TAB_BM);
    }

    @Override
    @SideOnly(Side.CLIENT)
    public boolean hasEffect(ItemStack stack) {
        return true;
    }

    @Override
    @SideOnly(Side.CLIENT)
    public void addInformation(ItemStack stack, World world, List<String> tooltip, ITooltipFlag flag) {
        tooltip.add(TextHelper.localizeEffect("tooltip.bloodmagic.experienceTome"));

        if (!stack.hasTagCompound())
            return;

        double storedExp = getStoredExperience(stack);

        tooltip.add(TextHelper.localizeEffect("tooltip.bloodmagic.experienceTome.exp", (int) storedExp));
        tooltip.add(TextHelper.localizeEffect("tooltip.bloodmagic.experienceTome.expLevel", (int) getLevelForExperience(storedExp)));
    }

    @Override
    public ActionResult<ItemStack> onItemRightClick(World world, EntityPlayer player, EnumHand hand) {
        ItemStack stack = player.getHeldItem(hand);
        if (!world.isRemote) {
            if (player.isSneaking())
                absorbOneLevelExpFromPlayer(stack, player);
            else
                giveOneLevelExpToPlayer(stack, player);
        }

        return new ActionResult<ItemStack>(EnumActionResult.SUCCESS, stack);
    }

    @Override
    public List<Pair<Integer, String>> getVariants() {
        List<Pair<Integer, String>> ret = new ArrayList<Pair<Integer, String>>();
        ret.add(new ImmutablePair<Integer, String>(0, "type=experiencetome"));
        return ret;
    }

    public void giveOneLevelExpToPlayer(ItemStack stack, EntityPlayer player) {
        float progress = player.experience;
        int expToNext = getExperienceForNextLevel(player.experienceLevel);

        int neededExp = (int) Math.ceil((1 - progress) * expToNext);
        float containedExp = (float) getStoredExperience(stack);

        System.out.println("Needed: " + neededExp + ", contained: " + containedExp + ", exp to next: " + expToNext);

        if (containedExp >= neededExp) {
            setStoredExperience(stack, containedExp - neededExp);
            addPlayerXP(player, neededExp);

            if (player.experienceLevel % 5 == 0) {
                float f = player.experienceLevel > 30 ? 1.0F : (float) player.experienceLevel / 30.0F;
                player.getEntityWorld().playSound(null, player.posX, player.posY, player.posZ, SoundEvents.ENTITY_PLAYER_LEVELUP, player.getSoundCategory(), f * 0.75F, 1.0F);
            }
        } else {
            setStoredExperience(stack, 0);
            addPlayerXP(player, (int) containedExp);
        }
    }

    public void absorbOneLevelExpFromPlayer(ItemStack stack, EntityPlayer player) {
        float progress = player.experience;

        if (progress > 0) {
            int expDeduction = (int) getExperienceAcquiredToNext(player);
            if (expDeduction > 0) {
                addPlayerXP(player, -expDeduction);
                addExperience(stack, expDeduction);
            }
        } else if (progress == 0 && player.experienceLevel > 0) {
            int expDeduction = getExperienceForNextLevel(player.experienceLevel - 1);
            addPlayerXP(player, -expDeduction);
            addExperience(stack, expDeduction);
        }
    }

    // Credits to Ender IO for some of the experience code, although now modified slightly for my convenience.
    public static int getPlayerXP(EntityPlayer player) {
        return (int) (getExperienceForLevel(player.experienceLevel) + (player.experience * player.xpBarCap()));
    }

    public static void addPlayerXP(EntityPlayer player, int amount) {
        int experience = Math.max(0, getPlayerXP(player) + amount);
        player.experienceTotal = experience;
        player.experienceLevel = getLevelForExperience(experience);
        int expForLevel = getExperienceForLevel(player.experienceLevel);
        player.experience = (float) (experience - expForLevel) / (float) player.xpBarCap();
    }

    public static void setStoredExperience(ItemStack stack, double exp) {
        NBTHelper.checkNBT(stack);

        NBTTagCompound tag = stack.getTagCompound();

        tag.setDouble("experience", exp);
    }

    public static double getStoredExperience(ItemStack stack) {
        NBTHelper.checkNBT(stack);

        NBTTagCompound tag = stack.getTagCompound();

        return tag.getDouble("experience");
    }

    public static void addExperience(ItemStack stack, double exp) {
        setStoredExperience(stack, getStoredExperience(stack) + exp);
    }

    public static int getExperienceForNextLevel(int currentLevel) {
        if (currentLevel < 16) {
            return 2 * currentLevel + 7;
        } else if (currentLevel < 31) {
            return 5 * currentLevel - 38;
        } else {
            return 9 * currentLevel - 158;
        }
    }

    //TODO: Change to calculation form.
    public static int getExperienceForLevel(int level) {
        if (level >= 21863) {
            return Integer.MAX_VALUE;
        }
        if (level == 0) {
            return 0;
        }
        int res = 0;
        for (int i = 0; i < level; i++) {
            res += getExperienceForNextLevel(i);
        }
        return res;
    }

    public static double getExperienceAcquiredToNext(EntityPlayer player) {
        return player.experience * player.xpBarCap();
    }

    public static int getLevelForExperience(double exp) {
        if (exp <= 352) {
            return (int) Math.floor(solveParabola(1, 6, -exp));
        } else if (exp <= 1507) {
            return (int) Math.floor(solveParabola(2.5, -40.5, 360 - exp));
        } else {
            return (int) Math.floor(solveParabola(4.5, -162.5, 2220 - exp));
        }
    }

    public static double solveParabola(double a, double b, double c) {
        return (-b + Math.sqrt(b * b - 4 * a * c)) / (2 * a);
    }
}