確率計算

calc.php

<?php

class Calc
{
    /** @var int */
    private $all;

    /** @var int[] */
    private $chance;

    public function __construct(int $all = 65536)
    {
        $this->all = $all;
    }

    public function addChance(int $id, int $chance): void
    {
        $this->chance[$id] = $chance;
    }

    public function calcChance(): ?int
    {
        $rand = mt_rand(1, $this->all);
        $last = 1;
        foreach ($this->chance as $id => $chance) {
            $cl = $chance + $last;
            if ($rand >= $last && $rand < $cl) {
                return $id;
            }
            $last += $chance;
        }
        return null;
    }
}