NSAttributedString到HTML到NSAttributedString的颜色降级

func convertAttributedStringToHTML(attributedString: NSAttributedString) -> String {
    var htmlString = ""
    
    attributedString.enumerateAttributes(in: NSRange(location: 0, length: attributedString.length), options: []) { (attributes, range, _) in
        let font = attributes[.font] as? UIFont
        let color = attributes[.foregroundColor] as? UIColor
        
        var htmlTag = ""
        if let font = font {
            if font.bold {
                htmlTag += "<b>"
            }
            if font.italic {
                htmlTag += "<i>"
            }
        }
        if let color = color {
            let hexColor = color.toHexString()
            htmlTag += "<font color=\"\(hexColor)\">"
        }
        
        let attributedSubstring = attributedString.attributedSubstring(from: range)
        let substring = attributedSubstring.string
        let htmlSubstring = "\(htmlTag)\(substring)</font>"
        
        htmlString += htmlSubstring
    }
    
    return htmlString
}

func convertHTMLToAttributedString(htmlString: String) -> NSAttributedString? {
    guard let data = htmlString.data(using: .utf8) else {
        return nil
    }
    
    let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [
        .documentType: NSAttributedString.DocumentType.html,
        .characterEncoding: String.Encoding.utf8.rawValue
    ]
    
    guard let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) else {
        return nil
    }
    
    return attributedString
}