I am getting the setspan error setspan starts before 0 at

I am getting the following error don't know what's wrong with my code. When its bold and italic then italic text sometimes removed and some time not and then get this error.

2018-11-10 19:34:03.032 16997-16997/com.pilum.apps.primalnotes E/AndroidRuntime: FATAL EXCEPTION: main Process: com.pilum.apps.primalnotes, PID: 16997 java.lang.IndexOutOfBoundsException: setSpan (-1 ... -1) starts before 0 at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1314) at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:680) at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:672) at com.apps.primalnotes.Fragments.EditorFragment.italicText2(EditorFragment.java:393) at com.apps.primalnotes.Fragments.EditorFragment.access$300(EditorFragment.java:48) at com.apps.primalnotes.Fragments.EditorFragment$5.onClick(EditorFragment.java:129) at android.view.View.performClick(View.java:6877) at android.view.View$PerformClick.run(View.java:26069) at android.os.Handler.handleCallback(Handler.java:789) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6938) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

 private void italicText2(){
      boolean italicExists = false;
      Spannable str = texto.getText();
      int selStart = texto.getSelectionStart();
      int selEnd = texto.getSelectionEnd();
      StyleSpan[] styleSpans = texto.getText().getSpans(selStart, selEnd, StyleSpan.class);

      for (StyleSpan styleSpan : styleSpans) {

          int oldStyle = styleSpan.getStyle();
          int spanStart = str.getSpanStart(styleSpan);
          int spanEnd = str.getSpanEnd(styleSpan);

          if (spanStart < texto.getSelectionStart()) {
              str.setSpan(new StyleSpan(oldStyle), spanStart, selStart, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
          }

          if (spanEnd > texto.getSelectionEnd()) {
              str.setSpan(new StyleSpan(oldStyle), selEnd, spanEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
          }
          if (selEnd > selStart) {
              if (oldStyle == Typeface.ITALIC) {
                  str.removeSpan(styleSpan);
                  italicExists = true;
              }
              if (oldStyle == Typeface.BOLD_ITALIC) {
                  str.setSpan(new StyleSpan(Typeface.BOLD), spanStart, spanEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                  italicExists = false;
              }
          }

      }

      if (!italicExists) {
          Log.d("Tag", "italic section entered");
          if (styleSpans.length > 0) {
              int lastSpanEnd = 0;
              for (StyleSpan styleSpan : styleSpans) {
                  int oldStyle = styleSpan.getStyle();
                  int spanStart = str.getSpanStart(styleSpan);
                  int spanEnd = str.getSpanEnd(styleSpan);


                  if (spanStart > lastSpanEnd) {
                      str.setSpan(new StyleSpan(Typeface.ITALIC), lastSpanEnd, spanStart, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                      Log.d("TAG", "if italic");
                  }

                  lastSpanEnd = spanEnd;
                  str.removeSpan(styleSpan);

                  if (oldStyle == Typeface.BOLD) {
                      str.setSpan(new StyleSpan(Typeface.BOLD_ITALIC), spanStart, spanEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                      Log.d("TAG", "Bold and Italic");
                  }
                  else {
                      **str.setSpan(new StyleSpan(Typeface.ITALIC), spanStart, spanEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);**
                      Log.d("TAG", "else italic");
                  }

                  if (spanStart < texto.getSelectionStart()) {
                      str.setSpan(new StyleSpan(oldStyle), spanStart, selStart, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                      Log.d("TAG", "oldstyle italic");
                  }

                  if (spanEnd > texto.getSelectionEnd()) {
                      str.setSpan(new StyleSpan(oldStyle), selEnd, spanEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                      Log.d("TAG", "old style end italic");
                  }
              }

              if (selEnd != lastSpanEnd) {
                  str.setSpan(new StyleSpan(Typeface.ITALIC), selStart, selEnd, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
              }
          }