<?php

namespace Modules\Core\Catalog\Services;

use Lunar\Models\ProductVariant;

/**
 * Generates a SKU for every ProductVariant missing one — extracted out of
 * Command\BackfillMissingSkusCommand (which becomes a thin CLI wrapper
 * around this, keeping --dry-run/progress-bar concerns out of the
 * reusable logic) so MigrateImport\Shopify\Services\ShopifyExportImporter can
 * also call it directly, once every product job in its import batch has
 * finished (see that class's own import()), with no CLI concerns at all.
 *
 * Format is "SKU-P{product_id}-V{variant_id}": deterministic and
 * guaranteed unique without a uniqueness check, since product_id/
 * variant_id already are. Only variants with a null `sku` are touched —
 * not an importer bug when one shows up after a Shopify import, the
 * source CSV rows genuinely had no `Variant SKU` value (see
 * MigrateImport\Shopify\Services\ShopifyExportImporter).
 */
class SkuBackfillService
{
    /**
     * @param  ?callable(ProductVariant, string): void  $onEach  invoked
     *   once per variant with the sku about to be written (or, when
     *   $dryRun is true, that WOULD be written) — the command's own
     *   --dry-run listing and progress bar hook in here without this
     *   service knowing anything about console output.
     * @return int the number of variants processed
     */
    public function backfill(bool $dryRun = false, ?callable $onEach = null): int
    {
        $query = ProductVariant::query()->whereNull('sku');
        $total = $query->count();

        if ($total === 0) {
            return 0;
        }

        $query->chunkById(500, function ($variants) use ($dryRun, $onEach) {
            foreach ($variants as $variant) {
                $sku = "SKU-P{$variant->product_id}-V{$variant->id}";

                if (! $dryRun) {
                    $variant->update(['sku' => $sku]);
                }

                if ($onEach !== null) {
                    $onEach($variant, $sku);
                }
            }
        });

        return $total;
    }
}