PocketMine-MP/src/block/utils/FortuneDropHelper.php

<?php

/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
 */

declare(strict_types=1);

namespace pocketmine\block\utils;

use pocketmine\item\enchantment\VanillaEnchantments;
use pocketmine\item\Item;
use pocketmine\item\VanillaItems;
use function max;
use function min;
use function mt_getrandmax;
use function mt_rand;

final class FortuneDropHelper{
	/**
	 * If a random number between 0-1 is greater than 2/(level+2), this multiplies the max drop amount by level+1, and
	 * picks a random amount between the minimum and multiplied maximum. Each level of fortune increases the chance of
	 * fortune activation, and also increases the maximum drop limit when activated.
	 *
	 * Otherwise, returns a random amount of the item between the minimum and original maximum.
	 *
	 * @param Item $usedItem The item used to break the block
	 * @param int  $min      Minimum amount
	 * @param int  $maxBase  Maximum amount, as if fortune level was 0
	 *
	 * @return int the number of items to drop
	 */
	public static function weighted(Item $usedItem, int $min, int $maxBase) : int{
		if($maxBase < $min){
			throw new \InvalidArgumentException("Maximum drop amount must be greater than or equal to minimum drop amount");
		}

		$fortuneLevel = $usedItem->getEnchantmentLevel(VanillaEnchantments::FORTUNE());

		return mt_rand($min,
			$fortuneLevel > 0 && mt_rand() / mt_getrandmax() > 2 / ($fortuneLevel + 2) ?
				$maxBase * ($fortuneLevel + 1) :
				$maxBase
		);
	}

	/**
	 * Increases the drop amount according to a binomial distribution. The function will roll maxBase+level times, and add 1
	 * if a random number between 0-1 is less than the given probability. Each level of fortune adds one extra roll.
	 *
	 * As many as maxBase+level items can be dropped. This applies even if the fortune level is 0.
	 *
	 * @param float $chance   The chance of adding 1 to the amount for each roll, must be in the range 0-1
	 * @param int   $min      Minimum amount
	 * @param int   $minRolls Number of rolls if fortune level is 0, added to fortune level to calculate total rolls
	 *
	 * @return int the number of items to drop
	 */
	public static function binomial(Item $usedItem, int $min, int $minRolls = 3, float $chance = 4 / 7) : int{
		$fortuneLevel = $usedItem->getEnchantmentLevel(VanillaEnchantments::FORTUNE());

		$count = $min;
		$rolls = $minRolls + $fortuneLevel;
		for($i = 0; $i < $rolls; ++$i){
			if(mt_rand() / mt_getrandmax() < $chance){
				++$count;
			}
		}

		return $count;
	}

	/**
	 * Grass have a fixed chance to drop wheat seed.
	 * Fortune level increases the maximum number of seeds that can be dropped.
	 * A discrete uniform distribution is used to determine the number of seeds dropped.
	 *
	 * TODO: I'm not sure this really belongs here, but it's preferable not to duplicate this code between grass and
	 * tall grass.
	 *
	 * @return Item[]
	 */
	public static function grass(Item $usedItem) : array{
		if(FortuneDropHelper::bonusChanceDivisor($usedItem, 8, 2)){
			return [
				VanillaItems::WHEAT_SEEDS()
			];
		}

		return [];
	}

	/**
	 * Adds the fortune level to the base max and picks a random number between the minimim and adjusted maximum.
	 * Each amount in the range has an equal chance of being picked.
	 *
	 * @param int $maxBase Maximum base amount, as if the fortune level was 0
	 *
	 * @return int the number of items to drop
	 */
	public static function discrete(Item $usedItem, int $min, int $maxBase) : int{
		if($maxBase < $min){
			throw new \InvalidArgumentException("Minimum base drop amount must be less than or equal to maximum base drop amount");
		}

		$max = $maxBase + $usedItem->getEnchantmentLevel(VanillaEnchantments::FORTUNE());
		return mt_rand($min, $max);
	}

	/**
	 * Calculates a chance of getting an extra bonus drop by reducing the chance divisor by a given amount per fortune
	 * level.
	 *
	 * @param int $divisorBase             The number to divide 1 by to get the chance, as if the fortune level was 0
	 * @param int $divisorSubtractPerLevel The amount to subtract from the divisor for each level of fortune
	 *
	 * @return bool whether the bonus drop should be added
	 */
	public static function bonusChanceDivisor(Item $usedItem, int $divisorBase, int $divisorSubtractPerLevel) : bool{
		$fortuneLevel = $usedItem->getEnchantmentLevel(VanillaEnchantments::FORTUNE());
		return mt_rand(1, max(1, $divisorBase - ($fortuneLevel * $divisorSubtractPerLevel))) === 1;
	}

	/**
	 * Calculates a chance of getting an extra bonus drop by increasing the chance by a fixed amount per fortune level.
	 *
	 * @param float $chanceBase          The base chance of getting a bonus drop, as if the fortune level was 0
	 * @param float $addedChancePerLevel The amount to add to the chance for each level of fortune
	 */
	public static function bonusChanceFixed(Item $usedItem, float $chanceBase, float $addedChancePerLevel) : bool{
		$fortuneLevel = $usedItem->getEnchantmentLevel(VanillaEnchantments::FORTUNE());
		$chance = min(1, $chanceBase + ($fortuneLevel * $addedChancePerLevel));
		return mt_rand() / mt_getrandmax() < $chance;
	}
}