RegularCustomers::findGroup

static function findGroup(int $dealCount)
{
	foreach (static::GROUPS as [$min, $max])
	{
		if($min == $max && $min == $dealCount)
		{
			return [$min, $max];
		}
		if($max > $min && $dealCount <= $max && $dealCount >= $min )
		{
			return [$min, $max];
		}
		if($max == 0 && $dealCount >= $min)
		{
			return [$min, $max];
		}
	}
	throw new SystemException("Could not find suitable group for {$dealCount} deals");
}