<?php
/**
 * Classifies gross product margin into severity bands.
 *
 * @package Kayvandra\MarginBeacon
 */

declare(strict_types=1);

namespace Kayvandra\MarginBeacon\Domain\Risk;

use Kayvandra\MarginBeacon\Domain\Money\MoneyAmount;
use Kayvandra\MarginBeacon\Domain\Money\MoneyMath;
use Kayvandra\MarginBeacon\Support\Constants;

/**
 * Pure severity classifier using integer cross-multiplication.
 */
final class SeverityClassifier {

	/**
	 * Classify from revenue and COGS amounts.
	 *
	 * @param MoneyAmount|null $revenue Revenue (null = unknown).
	 * @param MoneyAmount|null $cogs    COGS (null = missing cost → Unknown).
	 * @param array            $thresholds Keys critical_below, high_below, warning_below (scaled ints).
	 * @param bool             $evaluation_complete Whether all Safe invariants hold.
	 * @return array{severity:string,gross_profit:?MoneyAmount,severity_basis:array,reason_code:?string}
	 */
	public function classify( $revenue, $cogs, array $thresholds, $evaluation_complete = true ) {
		if ( null === $cogs ) {
			return $this->result( Severity::UNKNOWN, null, array(), 'MB_COST_MISSING' );
		}
		if ( null === $revenue ) {
			return $this->result( Severity::UNKNOWN, null, array(), 'MB_TOTALS_INVALID' );
		}
		if ( ! $evaluation_complete ) {
			return $this->result( Severity::UNKNOWN, null, array(), 'MB_PRICING_UNSUPPORTED' );
		}

		$profit = MoneyMath::sub( $revenue, $cogs );

		// Zero-revenue edge cases (PRD 9.9 / MB014 fully discounted line).
		if ( $revenue->is_zero() ) {
			if ( $cogs->is_positive() ) {
				return $this->result(
					Severity::CRITICAL,
					$profit,
					array(
						'case' => 'zero_revenue_positive_cogs',
					),
					'MB014'
				);
			}
			return $this->result( Severity::UNKNOWN, $profit, array( 'case' => 'zero_revenue_zero_cogs' ), null );
		}

		if ( $revenue->is_negative() ) {
			return $this->result( Severity::UNKNOWN, $profit, array(), 'MB_TOTALS_INVALID' );
		}

		$critical = (int) $thresholds['critical_below'];
		$high     = (int) $thresholds['high_below'];
		$warning  = (int) $thresholds['warning_below'];

		$vs_critical = MoneyMath::compare_margin_to_threshold(
			$profit,
			$revenue,
			$critical,
			Constants::THRESHOLD_SCALE
		);
		if ( $vs_critical['cmp'] < 0 ) {
			return $this->result( Severity::CRITICAL, $profit, $vs_critical, 'MB001' );
		}

		$vs_high = MoneyMath::compare_margin_to_threshold(
			$profit,
			$revenue,
			$high,
			Constants::THRESHOLD_SCALE
		);
		if ( $vs_high['cmp'] < 0 ) {
			return $this->result( Severity::HIGH, $profit, $vs_high, 'MB001' );
		}

		$vs_warning = MoneyMath::compare_margin_to_threshold(
			$profit,
			$revenue,
			$warning,
			Constants::THRESHOLD_SCALE
		);
		if ( $vs_warning['cmp'] < 0 ) {
			return $this->result( Severity::WARNING, $profit, $vs_warning, 'MB001' );
		}

		return $this->result( Severity::SAFE, $profit, $vs_warning, null );
	}

	/**
	 * @param string           $severity Severity.
	 * @param MoneyAmount|null $profit    Gross profit.
	 * @param array            $basis     Comparison basis.
	 * @param string|null      $reason    Reason code.
	 * @return array
	 */
	private function result( $severity, $profit, array $basis, $reason ) {
		return array(
			'severity'       => $severity,
			'gross_profit'   => $profit,
			'severity_basis' => $basis,
			'reason_code'    => $reason,
		);
	}
}