FillingInterpolatedAttributes.swift

var interpolatedFromAttributedText : NSAttributedString? {
    get {
        return fill(withInterpolatedAttributes: fromAttributedText)
    }
}
var interpolatedToAttributedText : NSAttributedString? {
    get {
        if toAttributedText != nil {
            return fill(withInterpolatedAttributes: toAttributedText!)
        }
        return nil
    }
}

private func fill(withInterpolatedAttributes attributedString: NSAttributedString?)->NSAttributedString {
    let mutableInterpolatedAttributedText = attributedString != nil ? 
                   NSMutableAttributedString(attributedString: attributedString!) : 
                   NSMutableAttributedString()
    mutableInterpolatedAttributedText.beginEditing()
    interpolatedAttributeStates.enumerateKeysAndObjects 
                            { (keyInAttrStates, objInAttrStates, stopInAttrStates) in
        guard let attrValuePerRangeString = objInAttrStates as? NSDictionary, 
              let attrStrKeyRawValue = keyInAttrStates as? String else { return }
              
        attrValuePerRangeString.enumerateKeysAndObjects { (keyInRange, objInRange, stopInRange) in
            guard let rangeString = keyInRange as? String else { return }
            let range = NSRangeFromString(rangeString)
            if range.location < mutableInterpolatedAttributedText.length {
                let key = NSAttributedString.Key(rawValue: attrStrKeyRawValue)
                let range = NSMakeRange(range.location, 
                                                           min(mutableInterpolatedAttributedText.length - 
                                                                                           range.location, 
                                                               range.length))
                if let decodedObject = LKTextDidChangeAction.decodeAttribute(from: objInRange as AnyObject, 
                                                           forAttributedStringKey: key) {
                    mutableInterpolatedAttributedText.addAttribute(key, 
                                                             value: decodedObject, 
                                                             range: range)
                } else {
                    mutableInterpolatedAttributedText.removeAttribute(key, range: range)
                }
            }
        }
    }
    
    mutableInterpolatedAttributedText.endEditing()
    return mutableInterpolatedAttributedText
}

private static func decodeAttribute(from object: AnyObject?, 
                     forAttributedStringKey key: NSAttributedString.Key)->AnyObject? {
    guard let dictionary = object as? NSDictionary else { return object }
    switch key {
    case .font:
        return UIFont.lk_dictDecode(dictionaryRepresentation: dictionary)
    case .foregroundColor,
         .backgroundColor,
         .strokeColor,
         .underlineColor,
         .strikethroughColor:
        return UIColor.lk_dictDecode(dictionaryRepresentation: dictionary)
    case .paragraphStyle:
        return NSParagraphStyle.lk_dictDecode(dictionaryRepresentation: dictionary)
    case .shadow:
        return NSShadow.lk_dictDecode(dictionaryRepresentation: dictionary)
    default:
        return object
    }
}