<?php

declare(strict_types=1);

namespace App;

final class InventoryService
{
    public function calculate(array $slot, float $distanceMm): array
    {
        $full = (float) ($slot['full_distance_mm'] ?? 0);
        $empty = (float) ($slot['empty_distance_mm'] ?? 0);
        $perUnit = max(0.01, (float) ($slot['distance_per_unit'] ?? 1));

        $denominator = $full - $empty;
        $ratio = $denominator === 0.0 ? 0.0 : (($distanceMm - $empty) / $denominator);
        $ratio = max(0.0, min(1.0, $ratio));

        $maxUnits = (int) max(0, round(abs($full - $empty) / $perUnit));
        $unitsEstimated = (int) max(0, min($maxUnits, round($ratio * $maxUnits)));
        $fillPercent = (int) round($ratio * 100);
        $alertBelowUnits = (int) ($slot['alert_below_units'] ?? 0);
        $state = $unitsEstimated < $alertBelowUnits ? 'critical' : 'ok';

        return [
            'distance_mm' => round($distanceMm, 2),
            'fill_ratio' => $ratio,
            'fill_percent' => $fillPercent,
            'units_estimated' => $unitsEstimated,
            'max_units' => $maxUnits,
            'alert_below_units' => $alertBelowUnits,
            'state' => $state,
        ];
    }
}