<?php

declare(strict_types=1);

namespace Domain\Models\ValueObjects;

use Domain\Enums\DiscountType;
use Domain\Models\Entities\Product;
use Money\Money;

/**
 * Represents a product discount (either a percentage or a fixed amount).
 *
 * Business rule: All discounts apply to the piece (sold unit), regardless of the product's invoicing unit.
 */
final readonly class DiscountValue
{
    private function __construct(
        public DiscountType $type,
        private ?int $percentage = null,
        private ?Money $amount = null
    ) {
        if ($type === DiscountType::PERCENT && $percentage === null) {
            throw new \DomainException(
                'Percentage rate must be provided for percentage discounts.'
            );
        }
        if ($percentage !== null && ($percentage < 0 || $percentage > 100)) {
            throw new \DomainException(
                'Percentage rate must be between 0 and 100.'
            );
        }
        if ($type === DiscountType::AMOUNT && $amount === null) {
            throw new \DomainException(
                'Amount must be provided for amount discounts.'
            );
        }
        if ($amount !== null && $amount->isNegative()) {
            throw new \DomainException(
                'Discount amount cannot be negative.'
            );
        }
    }

    public static function fromAmount(Money $amount): self
    {
        return new self(type: DiscountType::AMOUNT, amount: $amount);
    }

    public static function fromPercentage(int $percentageRate): self
    {
        return new self(type: DiscountType::PERCENT, percentage: $percentageRate);
    }

    public function value(): Money | int
    {
        if ($this->type === DiscountType::AMOUNT) {
            return $this->getAmount();
        }

        return $this->getPercentage();
    }

    public function isPercentage(): bool
    {
        return $this->type === DiscountType::PERCENT;
    }

    public function getPercentageRate(): float
    {
        return $this->getPercentage() / 100;
    }

    public function getPercentage(): int
    {
        if ($this->type !== DiscountType::PERCENT) {
            throw new \DomainException(
                'Cannot get percentage from a non-percentage discount.'
            );
        }

        if ($this->percentage === null) {
            throw new \DomainException(
                'Percentage rate must be set for percentage discounts.'
            );
        }

        return $this->percentage;
    }

    public function getAmount(): Money
    {
        if ($this->type !== DiscountType::AMOUNT) {
            throw new \DomainException(
                'Cannot get amount from a non-amount discount.'
            );
        }

        if ($this->amount === null) {
            throw new \DomainException(
                'Amount must be set for amount discounts.'
            );
        }

        return $this->amount;
    }

    public function calculateDiscountAmount(Money $basePrice): Money
    {
        if ($this->type === DiscountType::AMOUNT) {
            $amount = $this->getAmount();
            if (! $amount->getCurrency()->equals($basePrice->getCurrency())) {
                throw new \DomainException('Currency mismatch.');
            }

            return $amount;
        }

        $rate = $this->getPercentageRate();

        return $basePrice->multiply((string) $rate, Product::ROUNDING);
    }
}