kiri-rpc/Luckdraw.php

<?php

namespace Kiri\Rpc;

use Exception;

class Luckdraw
{


	/**
	 * @param array $goods
	 * @param string $wight
	 * @return mixed
	 * @array = [
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 *     ['name'=> '商品名称', 'probability'=> '概率', 'total'=> '库存'],
	 * ]
	 *
	 * @uses $reward = Lucked::luck($data);
	 */
	public static function luck(array $goods, string $wight = 'probability'): mixed
	{
		static $class = null;
		if ($class === null) $class = new Luckdraw();

		if (empty($goods)) return null;

		$array = $prob = $alias = [];

		$defaultIndex = 0;
		foreach ($goods as $key => $val) {
			if ($val[$wight] == 0) $defaultIndex = $key;
			$array[] = (float)$val[$wight];
		}
		$array[$defaultIndex] = 1 - array_sum($array);
		$class->ket($array, $prob, $alias);

		$result = $class->generation($array, $prob, $alias);
		if (!isset($goods[$result])) {
			return null;
		}
		return $goods[$result];
	}

	/**
	 * @param $data
	 * @param $prob
	 * @param $alias
	 * @return mixed
	 */
	private function generation($data, $prob, $alias): mixed
	{
		$nums = count($prob) - 1;

		$MAX_P = $this->getMin($data);         // 假设最小的几率是万分之一
		$coin_toss = rand(1, $MAX_P) / $MAX_P; // 抛出硬币

		$col = rand(0, $nums);              // 随机落在一列
		$b_head = $coin_toss < $prob[$col]; // 判断是否落在原色

		return $b_head ? $col : @$alias[$col];
	}

	/**
	 * @param $num
	 * @return string
	 */
	private function getMin($num): string
	{
		$def = current($num);
		foreach ($num as $val) {
			if ($val < $def) {
				$def = $val;
			}
		}

		$length = $this->getFloatLength($def) + 1;

		return sprintf('1%0' . $length . 'd', 0);
	}

	/**
	 * @param $float
	 * @return int
	 */
	private function getFloatLength($float): int
	{
		$ex = explode('.', 1 - $float);

		return strlen(end($ex));
	}

	/**
	 * @param array $data
	 * @param array $prob
	 * @param array $alias
	 */
	private function ket(array $data, array &$prob, array &$alias)
	{
		$nums = count($data);
		$small = $large = [];
		for ($i = 0; $i < $nums; ++$i) {
			$data[$i] = $data[$i] * $nums; // 扩大倍数，使每列高度可为1

			/** 分到两个数组，便于组合 */
			if ($data[$i] < 1) {
				$small[] = $i;
			} else {
				$large[] = $i;
			}
		}

		/** 将超过1的色块与原色拼凑成1 */
		while (!empty($small) && !empty($large)) {
			$n_index = array_shift($small);
			$a_index = array_shift($large);

			$prob[$n_index] = $data[$n_index];
			$alias[$n_index] = $a_index;
			// 重新调整大色块
			$data[$a_index] = ($data[$a_index] + $data[$n_index]) - 1;

			if ($data[$a_index] < 1) {
				$small[] = $a_index;
			} else {
				$large[] = $a_index;
			}
		}

		/** 剩下大色块都设为1 */
		while (!empty($large)) {
			$n_index = array_shift($large);
			$prob[$n_index] = 1;
		}

		/** 一般是精度问题才会执行这一步 */
		while (!empty($small)) {
			$n_index = array_shift($small);
			$prob[$n_index] = 1;
		}
	}


}