ldc-boutique-cnc-sable/tests/Unit/Domain/Models/ValueObjects/DiscountRateTest.php

<?php

declare(strict_types=1);

use Domain\Models\ValueObjects\DiscountRate;
use Money\Money;

describe(DiscountRate::class, function (): void {
    it('instantiates from basis points and exposes ratio and percentage', function (): void {
        // GIVEN
        $basisPoints = 1550;

        // WHEN
        $rate = DiscountRate::fromBasisPoints($basisPoints);

        // THEN
        expect($rate->basisPoints())->toBe(1550)
            ->and($rate->ratio())->toBe(0.155)
            ->and($rate->percentage())->toBe(15.5)
            ->and($rate->isZero())->toBeFalse();
    });

    it('creates a zero rate', function (): void {
        // GIVEN / WHEN
        $rate = DiscountRate::zero();

        // THEN
        expect($rate->basisPoints())->toBe(0)
            ->and($rate->isZero())->toBeTrue();
    });

    it('creates a rate from a percentage', function (int | float $percentage, int $expectedBasisPoints): void {
        // GIVEN / WHEN
        $rate = DiscountRate::fromPercentage($percentage);

        // THEN
        expect($rate->basisPoints())->toBe($expectedBasisPoints);
    })->with([
        'integer percent' => [15, 1500],
        'decimal percent' => [5.5, 550],
        'zero'            => [0, 0],
        'full'            => [100, 10000],
    ]);

    it('creates a rate from a ratio without float drift', function (float $ratio, int $expectedBasisPoints): void {
        // GIVEN / WHEN
        $rate = DiscountRate::fromRatio($ratio);

        // THEN
        expect($rate->basisPoints())->toBe($expectedBasisPoints);
    })->with([
        'ten percent'     => [0.1, 1000],
        'classic drift'   => [0.29, 2900], // 0.29 * 10000 = 2899.9999999999995 in IEEE 754
        'five point five' => [0.055, 550],
    ]);

    it('computes the rate of a fixed amount discount on a base price', function (): void {
        // GIVEN
        $basePrice = Money::EUR(1000);
        $discount  = Money::EUR(200);

        // WHEN
        $rate = DiscountRate::fromAmounts($discount, $basePrice);

        // THEN
        expect($rate->basisPoints())->toBe(2000)
            ->and($rate->ratio())->toBe(0.2);
    });

    it('rounds the rate of a fixed amount discount to the nearest basis point', function (): void {
        // GIVEN
        $basePrice = Money::EUR(300);
        $discount  = Money::EUR(100); // 33.333...%

        // WHEN
        $rate = DiscountRate::fromAmounts($discount, $basePrice);

        // THEN
        expect($rate->basisPoints())->toBe(3333);
    });

    it('caps a fixed amount discount greater than the base price at 100 percent', function (): void {
        // GIVEN
        $basePrice = Money::EUR(500);
        $discount  = Money::EUR(900);

        // WHEN
        $rate = DiscountRate::fromAmounts($discount, $basePrice);

        // THEN
        expect($rate->basisPoints())->toBe(10000);
    });

    it('returns a zero rate when the base price or the discount is not positive', function (): void {
        // GIVEN / WHEN
        $noPrice    = DiscountRate::fromAmounts(Money::EUR(100), Money::EUR(0));
        $noDiscount = DiscountRate::fromAmounts(Money::EUR(0), Money::EUR(1000));

        // THEN
        expect($noPrice->isZero())->toBeTrue()
            ->and($noDiscount->isZero())->toBeTrue();
    });

    it('applies the rate to an amount', function (): void {
        // GIVEN
        $rate   = DiscountRate::fromPercentage(15);
        $amount = Money::EUR(1000);

        // WHEN
        $discount = $rate->applyTo($amount);

        // THEN
        expect($discount->getAmount())->toBe('150');
    });

    it('formats the rate as a percentage', function (int $basisPoints, string $expected): void {
        // GIVEN
        $rate = DiscountRate::fromBasisPoints($basisPoints);

        // WHEN
        $formatted = (string) $rate;

        // THEN
        expect($formatted)->toBe($expected);
    })->with([
        'integer'  => [1500, '15 %'],
        'decimal'  => [550, '5.5 %'],
        'zero'     => [0, '0 %'],
        'hundred'  => [10000, '100 %'],
    ]);

    it('compares two rates', function (): void {
        // GIVEN
        $a = DiscountRate::fromPercentage(10);
        $b = DiscountRate::fromRatio(0.1);
        $c = DiscountRate::fromPercentage(20);

        // WHEN / THEN
        expect($a->equals($b))->toBeTrue()
            ->and($a->equals($c))->toBeFalse();
    });

    it('throws when the rate is negative or above 100 percent', function (int $basisPoints): void {
        // GIVEN / WHEN
        $action = fn () => DiscountRate::fromBasisPoints($basisPoints);

        // THEN
        expect($action)->toThrow(\InvalidArgumentException::class);
    })->with([
        'negative'        => [-1],
        'above 100%'      => [10001],
    ]);
});