Setting spans "on-the-go" in EditText using TextWatcher

Question

I want to set spans while user is typing. I have configured interface for choosing which span to apply, but I'm having problems with spans setting.

1. When I'm setting span on the whole word it works properly, but I can't remove text style by putting on it StyleSpan(NORMAL).
2. For some strange reasons inserting raw text between two words written with some span makes it "spanned" too.
3. Inserting long WORDS makes app work so slow that it's not possible to type

I have checked with debugger so I can say that viewModel works properly

Is it possible to solve this bugs still using spans?

class TextEditor(private val activity: AppCompatActivity) : TextWatcher {
    private var _ignore = true
    private var _backspace = true
    private var inputtedStart = 0
    private var inputtedEnd = 0
    private var inputtedBefore = 0

    val viewModel: TextEditorViewModel =
        ViewModelProvider(activity)[TextEditorViewModel::class.java]


    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        //checking if some text was deleted not inserted 
        _backspace = before <= count
        inputtedStart = start
        inputtedBefore = before
        inputtedEnd = inputtedStart + count
    }

    override fun afterTextChanged(s: Editable) {
        if (_ignore && _backspace) {
            _ignore = false
            if (viewModel.bold && viewModel.italic) {
                s.setSpan(StyleSpan(Typeface.BOLD_ITALIC),
                    inputtedStart,
                    inputtedEnd,
                    Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)
            } else {
                s.setSpan(StyleSpan(Typeface.NORMAL),
                    inputtedStart,
                    inputtedEnd,
                    Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)
            }
            if (viewModel.bold) {
                s.setSpan(StyleSpan(Typeface.BOLD),
                    inputtedStart,
                    inputtedEnd,
                    Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)
            }
            if (viewModel.italic) {
                s.setSpan(StyleSpan(Typeface.ITALIC),
                    inputtedStart,
                    inputtedEnd,
                    Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)
            }
            _ignore = true
        }
    }
}