Test Decimals

TestTotalController.php

<?php

namespace App\Http\Controllers;

class TestTotalController extends Controller
{
    private $taxRate = 8.875;

    public function show()
    {
        $price1 = $this->getItem1Price();
        $price1 = $price1 + $this->getTaxAmount($price1);
        $centPrice1 = (new Money($price1, Money::MODE_DOLLAR))->getCentValue();

        $price2 = $this->getItem2Price();
        $price2 = $price2 + $this->getTaxAmount($price2);
        $centPrice2 = (new Money($price2, Money::MODE_DOLLAR))->getCentValue();

        dd('expected total: 41.9168$ (41.92$ -> 4192 cents), actual total: ' . ($centPrice1 + $centPrice2) . ' cents');
    }

    protected function getItem1Price()
    {
        // dollars
        return 14.75; // with taxes it would be 16.05906
    }

    protected function getItem2Price()
    {
        // dollars
        return 23.75; // with taxes it would be 25.85781
    }

    protected function getTaxAmount($sum)
    {
        return ($this->taxRate / 100) * $sum;
    }
}


class Money
{
    public const MODE_CENT   = 1;
    public const MODE_DOLLAR = 2;

    /** @var int */
    private $centValue;

    /** @var float */
    private $dollarValue;

    public function __construct($amount, $mode = self::MODE_CENT)
    {
        $this->setAmount($amount, $mode);
    }

    public function setAmount($amount, $mode = self::MODE_CENT) : void
    {
        if ($mode === self::MODE_CENT) {
            $this->setCentValue($amount);
            $this->setDollarValue(round($amount / 100, 2));
        } elseif ($mode === self::MODE_DOLLAR) {
            $this->setCentValue(round($amount, 2) * 100);
            $this->setDollarValue($amount);
        } else {
            throw new \Exception("Mode '$mode' is incorrect'");
        }
    }

    public function getCentValue() : int
    {
        return $this->centValue;
    }

    public function getDollarValue() : float
    {
        return $this->dollarValue;
    }

    public function getDollarValueAsString(int $decimals = 2) : string
    {
        $stringCentValue = (string)$this->getCentValue();
        $dollar = substr($stringCentValue, 0, strlen($stringCentValue)-2);
        $cent = substr($stringCentValue, -2);

        if ($decimals >= 2) {
            $cent = str_pad($cent, $decimals, '0');
        } else {
            $cent = substr($cent, 0, $decimals);
        }

        $result = $dollar;

        if (strlen($cent) > 0) {
            $result .= ".{$cent}";
        }

        return $result;
    }

    /**
     * @param mixed $centValue
     */
    private function setCentValue($centValue) : void
    {
        $this->centValue = intval($centValue);
    }

    /**
     * @param mixed $dollarValue
     */
    private function setDollarValue($dollarValue) : void
    {
        $this->dollarValue = floatval($dollarValue);
    }
}