WitShop/app/Models/EmailTemplate.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class EmailTemplate extends Model
{
    protected $fillable = ['key', 'label', 'subject', 'body', 'variables'];
    protected $casts = ['variables' => 'array'];

    public static function getByKey(string $key): ?self
    {
        return static::where('key', $key)->first();
    }

    public function renderBody(array $data): string
    {
        $body = $this->body;
        foreach ($data as $k => $v) {
            $body = str_replace('{{' . $k . '}}', (string) $v, $body);
        }
        return $body;
    }

    public function renderSubject(array $data): string
    {
        $subject = $this->subject;
        foreach ($data as $k => $v) {
            $subject = str_replace('{{' . $k . '}}', (string) $v, $subject);
        }
        return $subject;
    }
}