<?php
namespace app\models\search;

use app\models\core\Company as CoreCompany;
use yii\db\Query;
use yii\helpers\ArrayHelper;

class Company extends CoreCompany
{
    public static function listFirstLetters()
    {
        $query = new Query();

        $query->select(['first_letter'])
            ->from(self::tableName())
            ->groupBy(['first_letter'])
            ->orderBy(['first_letter' => SORT_ASC]);

        $letters = $query->column();
        $letters = array_filter($letters, function($letter) {
            return preg_match('/[A-Z0-9]/i', $letter);
        });

        return array_values($letters);
    }
}