<?php
/**
 * Applies a validated coupon discount to the running total.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Domain\Pricing\Modifiers;

use Bookline\Domain\Coupon\CouponValidator;
use Bookline\Domain\Pricing\Money;
use Bookline\Domain\Pricing\PriceContext;
use Bookline\Domain\Pricing\PriceModifier;
use Bookline\Domain\Shared\DomainException;

/**
 * Priority 50 — coupon discount.
 *
 * @since 0.1.0
 */
final class CouponDiscount implements PriceModifier {

	/**
	 * Constructor.
	 *
	 * @param CouponValidator $validator Coupon validator.
	 */
	public function __construct(
		private CouponValidator $validator = new CouponValidator(),
	) {}

	/**
	 * Priority.
	 *
	 * @since 0.1.0
	 */
	public function priority(): int {
		return 50;
	}

	/**
	 * Subtract coupon discount when a coupon is present and valid.
	 *
	 * @param PriceContext $ctx     Context.
	 * @param Money        $running Running total.
	 *
	 * @throws DomainException When a coupon is present but invalid.
	 *
	 * @since 0.1.0
	 */
	public function apply( PriceContext $ctx, Money $running ): Money {
		$coupon = $ctx->coupon();
		if ( null === $coupon ) {
			return $running;
		}

		$result = $this->validator->validate( $coupon, $ctx, $running );
		if ( $result->is_err() ) {
			throw new DomainException(
				htmlspecialchars( $result->error_code(), ENT_QUOTES, 'UTF-8' ),
				htmlspecialchars( $result->error_message(), ENT_QUOTES, 'UTF-8' )
			);
		}

		$discount = $this->validator->discount_amount( $coupon, $running );
		return $running->subtract( $discount );
	}

	/**
	 * Discount amount for a validated coupon (or zero).
	 *
	 * @param PriceContext $ctx     Context.
	 * @param Money        $running Pre-discount total.
	 *
	 * @throws DomainException When a coupon is present but invalid.
	 *
	 * @since 0.1.0
	 */
	public function discount_amount( PriceContext $ctx, Money $running ): Money {
		$coupon = $ctx->coupon();
		if ( null === $coupon ) {
			return Money::zero( $running->currency() );
		}

		$result = $this->validator->validate( $coupon, $ctx, $running );
		if ( $result->is_err() ) {
			throw new DomainException(
				htmlspecialchars( $result->error_code(), ENT_QUOTES, 'UTF-8' ),
				htmlspecialchars( $result->error_message(), ENT_QUOTES, 'UTF-8' )
			);
		}

		return $this->validator->discount_amount( $coupon, $running );
	}
}