[SWIFT]이미지 비율 계산

func sizeToFillWidthOfSize(_ size:CGSize) -> CGSize {
    
    guard let thumbnail = thumbnail else {
      return size
    }
    
    let imageSize = thumbnail.size
    var returnSize = size
    
    let aspectRatio = imageSize.width / imageSize.height
    
    returnSize.height = returnSize.width / aspectRatio
    
    if returnSize.height > size.height {
      returnSize.height = size.height
      returnSize.width = size.height * aspectRatio
    }
    
    return returnSize
  }