如何查找UITextView (iOS)中哪个字符被截断？

func findTruncatedCharacter(in textView: UITextView) -> Int? {
    let text = textView.text ?? ""
    let visibleRect = textView.bounds
    let font = textView.font ?? UIFont.systemFont(ofSize: UIFont.systemFontSize)
    
    let maxSize = CGSize(width: visibleRect.width, height: CGFloat.greatestFiniteMagnitude)
    let textRect = text.boundingRect(with: maxSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedString.Key.font: font], context: nil)
    
    if textRect.height > visibleRect.height {
        let characterIndex = findCharacterIndex(for: text, in: visibleRect, with: font)
        return characterIndex
    }
    
    return nil
}

func findCharacterIndex(for text: String, in visibleRect: CGRect, with font: UIFont) -> Int {
    var accumulatedHeight: CGFloat = 0
    
    for (index, character) in text.enumerated() {
        let characterString = String(character)
        let characterSize = characterString.size(withAttributes: [NSAttributedString.Key.font: font])
        
        if accumulatedHeight + characterSize.height > visibleRect.height {
            return index - 1
        }
        
        accumulatedHeight += characterSize.height
    }
    
    return -1
}