<?php

/**

 * 红包分配算法

 *

 *      example

 *      $coupon = new Coupon(200, 5);

 *      $res = $coupon->handle();

 *      print_r($res);

 * @author Flc <2018-04-06 20:09:53>

 * @see http://flc.ren | http://flc.io | https://github.com/flc1125

 */

class Coupon

{

    /**

     * 红包金额

     * @var float

     */

    protected $amount;

    /**

     * 红包个数

     * @var int

     */

    protected $num;

    /**

     * 领取的红包最小金额

     * @var float

     */

    protected $coupon_min;

    /**

     * 红包分配结果

     * @var array

     */

    protected $items = [];

    /**

     * 初始化

     * @param float $amount     红包金额（单位：元）最多保留2位小数

     * @param int   $num        红包个数

     * @param float $coupon_min 每个至少领取的红包金额

     */

    public function __construct($amount, $num = 1, $coupon_min = 0.01)

    {

        $this->amount = $amount;

        $this->num = $num;

        $this->coupon_min = $coupon_min;

    }

    /**

     * 处理返回

     * @return array

     */

    public function handle()

    {

        // A. 验证

        if ($this->amount < $validAmount = $this->coupon_min * $this->num) {

            throw new Exception('红包总金额必须≥'.$validAmount.'元');

        }

        // B. 分配红包

        $this->apportion();

        return [

            'items' => $this->items,

        ];

    }

    /**

     * 分配红包

     */

    protected function apportion()

    {

        $num = $this->num;  // 剩余可分配的红包个数

        $amount = $this->amount;  //剩余可领取的红包金额

        while ($num >= 1) {

            // 剩余一个的时候，直接取剩余红包

            if ($num == 1) {

                $coupon_amount = $this->decimal_number($amount);

            } else {

                $avg_amount = $this->decimal_number($amount / $num);  // 剩余的红包的平均金额

                $coupon_amount = $this->decimal_number(

                    $this->calcCouponAmount($avg_amount, $amount, $num)

                );

            }

            $this->items[] = $coupon_amount; // 追加分配

            $amount -= $coupon_amount;

            --$num;

        }

        shuffle($this->items);  //随机打乱

    }

    /**

     * 计算分配的红包金额

     *

     * @param float $avg_amount 每次计算的平均金额

     * @param float $amount     剩余可领取金额

     * @param int   $num        剩余可领取的红包个数

     * @return float

     */

    protected function calcCouponAmount($avg_amount, $amount, $num)

    {

        // 如果平均金额小于等于最低金额，则直接返回最低金额

        if ($avg_amount <= $this->coupon_min) {

            return $this->coupon_min;

        }

        // 浮动计算

        $coupon_amount = $this->decimal_number($avg_amount * (1 + $this->apportionRandRatio()));

        // 如果低于最低金额或超过可领取的最大金额，则重新获取

        if ($coupon_amount < $this->coupon_min

            || $coupon_amount > $this->calcCouponAmountMax($amount, $num)

        ) {

            return $this->calcCouponAmount($avg_amount, $amount, $num);

        }

        return $coupon_amount;

    }

    /**

     * 计算分配的红包金额-可领取的最大金额

     * @param float $amount

     * @param int   $num

     */

    protected function calcCouponAmountMax($amount, $num)

    {

        return $this->coupon_min + $amount - $num * $this->coupon_min;

    }

    /**

     * 红包金额浮动比例

     */

    protected function apportionRandRatio()

    {

        // 60%机率获取剩余平均值的大幅度红包（可能正数、可能负数）

        if (rand(1, 100) <= 60) {

            return rand(-70, 70) / 100; // 上下幅度70%

        }

        return rand(-30, 30) / 100; // 其他情况，上下浮动30%；

    }

    /**

     * 格式化金额，保留2位

     * @param float $amount

     * @return float

     */

    protected function decimal_number($amount)

    {

        return sprintf('%01.2f', round($amount, 2));

    }

}

// 例子

$price_total = 0;

$total = $surplus_total = 30;

$max_num = $surplus_num = 8;

echo "总共{$total}元，随机生成{$max_num}个红包".'</br>';

for($i=0;$i<$max_num;$i++){

    $coupon = new Coupon($surplus_total, $surplus_num, 0.01);

    $res = $coupon->handle();

    $money = $res['items'][0];

    $price_total += $money;

    $surplus_total = bcsub($surplus_total, $money, 2);　　//解决高精度问题

    echo '第'.($i+1).'个随机红包：'.$money.'还剩下'.($surplus_total).'元'.'<br>';

    $surplus_num--;

}