FurusatoTax.php

<?php

class FurusatoTax
{
    private int $donationPrice;
    private float $incomeTaxRate;

    /**
     * FurusatoTax constructor.
     * @param int $donationPrice
     * @param float $incomeTaxRate
     */
    public function __construct(int $donationPrice, float $incomeTaxRate)
    {
        $this->donationPrice = $donationPrice;
        $this->incomeTaxRate = $incomeTaxRate;
    }

    public function __invoke(): int
    {
        return $this->deductionByIncome() + $this->deductionBaseResidentTax() + $this->deductionSpecialResidentTax();
    }

    public function deductionByIncome(): int
    {
        return ($this->donationPrice - 2000) * $this->incomeTaxRate;
    }

    public function deductionBaseResidentTax(): int
    {
        return ($this->donationPrice - 2000) * 0.1;
    }

    public function deductionSpecialResidentTax(): int
    {
        return ($this->donationPrice - 2000) * (1 - 0.1) - $this->incomeTaxRate;
    }
}