<?php
/**
 * Tax calculation — inclusive or exclusive per tax class.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Domain\Pricing\Modifiers;

use Bookline\Domain\Pricing\Money;
use Bookline\Domain\Pricing\PriceContext;
use Bookline\Domain\Pricing\PriceModifier;

/**
 * Priority 60 — tax on the post-discount amount.
 *
 * Exclusive: tax is added to the running total.
 * Inclusive: catalogue prices already include tax; running total is unchanged and the
 * tax component is extracted with half-away-from-zero rounding.
 *
 * @since 0.1.0
 */
final class TaxCalculation implements PriceModifier {

	/**
	 * Priority.
	 *
	 * @since 0.1.0
	 */
	public function priority(): int {
		return 60;
	}

	/**
	 * Apply exclusive tax (inclusive is a no-op on the running total).
	 *
	 * @param PriceContext $ctx     Context.
	 * @param Money        $running Running total.
	 *
	 * @since 0.1.0
	 */
	public function apply( PriceContext $ctx, Money $running ): Money {
		$rate = $ctx->tax_rate();
		if ( 0 === $rate->percent() || $rate->is_inclusive() ) {
			return $running;
		}
		return $running->add( $this->tax_amount( $ctx, $running ) );
	}

	/**
	 * Tax component for the given post-discount amount.
	 *
	 * @param PriceContext $ctx     Context.
	 * @param Money        $running Post-discount amount (tax-inclusive or exclusive base).
	 *
	 * @since 0.1.0
	 */
	public function tax_amount( PriceContext $ctx, Money $running ): Money {
		$rate = $ctx->tax_rate();
		if ( 0 === $rate->percent() ) {
			return Money::zero( $running->currency() );
		}

		if ( $rate->is_inclusive() ) {
			// tax = gross × rate / (100 + rate), half-away-from-zero.
			$tax_minor = Money::divide_round(
				$running->amount_minor() * $rate->percent(),
				100 + $rate->percent()
			);
			return new Money( $tax_minor, $running->currency() );
		}

		return $running->percent( $rate->percent() );
	}
}