Inserts spaces after every block of 4 digits

CreditCardFormattingTextWatcher.kt

class CreditCardTextWatcher(private val maxLength: Int) : TextWatcher {

    override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {}
    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {}

    override fun afterTextChanged(s: Editable) {
        val textLength = s.length
        // first remove any previous span
        val spans = s.getSpans(0, s.length, SpaceSpan::class.java)
        for (i in spans.indices) {
            s.removeSpan(spans[i])
        }
        // then truncate to max length
        if (maxLength > 0 && textLength > maxLength - 1) {
            s.replace(maxLength, textLength, "")
        }
        // finally add margin spans
        for (i in 1..(textLength - 1) / 4) {
            val end = i * 4
            val start = end - 1
            val marginSPan = SpaceSpan()
            s.setSpan(marginSPan, start, end, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
        }
    }
}

public class SpaceSpan extends ReplacementSpan {

    private static final String SPACE = " ";

    @Override
    public int getSize(@NonNull Paint paint, CharSequence text, int start, int end, Paint.FontMetricsInt fm) {
        float padding = paint.measureText(SPACE, 0, 1);
        float textSize = paint.measureText(text, start, end);
        return (int) (padding + textSize);
    }

    @Override
    public void draw(@NonNull Canvas canvas, CharSequence text, int start, int end, float x, int top, int y,
                     int bottom, @NonNull Paint paint) {
        canvas.drawText(text.subSequence(start, end) + SPACE, x, y, paint);
    }
}