landing-api/app/Rules/UniqueTranslatedSlug.php

<?php

declare(strict_types=1);

namespace App\Rules;

use Closure;
use Illuminate\Contracts\Validation\ValidationRule;
use Illuminate\Database\Eloquent\Model;

/**
 * Enforces slug uniqueness per locale.
 *
 * Slugs live inside a JSON map, which no database unique index can cover, so
 * the check happens here: for each locale in the payload, no *other* row may
 * already use that slug in that same locale. The same slug in two different
 * languages is fine.
 */
class UniqueTranslatedSlug implements ValidationRule
{
    /**
     * @param  class-string<Model>  $model
     */
    public function __construct(
        protected string $model,
        protected ?int $ignoreId = null,
        protected string $column = 'slug',
    ) {}

    public function validate(string $attribute, mixed $value, Closure $fail): void
    {
        $translations = is_string($value)
            ? [app()->getLocale() => $value]
            : (array) $value;

        foreach ($translations as $locale => $slug) {
            if (blank($slug)) {
                continue;
            }

            $query = $this->model::query()
                ->where("{$this->column}->{$locale}", $slug);

            if ($this->ignoreId !== null) {
                $query->whereKeyNot($this->ignoreId);
            }

            // Soft-deleted rows still hold their slug, so include them —
            // otherwise restoring one would resurrect a duplicate.
            if (method_exists($this->model, 'bootSoftDeletes')) {
                $query->withTrashed();
            }

            if ($query->exists()) {
                $fail(__('rules.slug.unique', [
                    'slug' => $slug,
                    'locale' => (string) $locale,
                ]));

                return;
            }
        }
    }
}