根据总金额生成指定个人的随机红包数量

/**
 * Class RedPacket
 * 根据总金额生成指定个人的随机红包数量：
 * 1.最小金额0.01元；
 * 2.每份红包的最大上限；
 * 3.总金额不一定发放完毕，会存在剩余金额，按照业务流程自己处理。
 */
class RedPacket
{
    //总金额
    private $total = 0;

    //红包数量
    private $amount = 0;

    //最小红包金额
    private $min = 0.01;

    //最大红包金额
    private $max = 0.01;

    public function __construct(float $total, int $amount, float $min = 0.01, float $max = 0.01)
    {
        $this->total = $total;
        $this->amount = $amount;
        $this->min = $min;
        if ( $this->amount * $this->min > $total ) {
            throw new \Exception('发放红包的总额超过了总金额！');
        }
        $this->max = $max;
    }

    /**
     * 生成随机红包组
     *
     * @return array
     * @throws \Exception
     */
    public function getPacket() : array
    {
        $total = $this->total;
        if ( $this->amount * $this->min > $total ) {
            throw new \Exception('发放红包的总额超过了总金额！');
        }
        $redPacket = [];
        for ($i = 1; $i < $this->amount; $i++) {
            // 随机安全上限
            $safe_total = ($total - ($this->amount - $i) * $this->min) / ($this->amount - $i);
            if ( $this->min < $safe_total ) {
                // 生成区间随机整数
                $money = mt_rand($this->min * 100, $safe_total * 100) / 100;
            } else {
                $money = $this->min;
            }
            // 每份金额的最大额度上限限制
            if ( $money > $this->max ) {
                $money = $this->max;
            }
            $total = floatval($total - $money);
            $redPacket[] = [
                'money' => $money,
                'surplus' => $total,
            ];
        }
        $surplus = 0;
        // 每份金额的最大额度上限限制
        if ( $total > $this->max ) {
            $surplus = floatval($total - $this->max);
            $total = $this->max;
        }
        // 最后一份红包数据
        $redPacket[] = [
            'money' => $total,
            'surplus' => $surplus,
        ];
        return $redPacket;
    }
}