Masked Input EditText

addTextWatcher.kt

etCardNumber.doAfterTextChanged { editable ->
    if (editable == null) return
    val paddingPx = etCardNumber.paint.measureText("X").toInt()
    formatDebitCard(editable, paddingPx)
}

formatDebitCard.kt

private fun formatDebitCard(editable: Editable, paddingPx: Int) {
    val textLength = editable.length
    // first remove any previous span
    val spans = editable.getSpans(
        0, editable.length,
        PaddingRightSpan::class.java
    )
    for (i in spans.indices) {
        editable.removeSpan(spans[i])
    }

    // adding spans 
    for (i in 0 until textLength) {
        // 000`0` 000`0` 000`0` 0000
        if (i in arrayOf(3, 7, 11)) {
            val marginSPan =
                PaddingRightSpan(paddingPx)
            editable.setSpan(marginSPan, i, i + 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
        }
    }
}

PaddingRightSpan.kt

class PaddingRightSpan(private val mPadding: Int) : ReplacementSpan() {
    override fun getSize(
        paint: Paint, text: CharSequence,
        start: Int, end: Int,
        fm: Paint.FontMetricsInt?
    ): Int {
        val widths = FloatArray(end - start)
        paint.getTextWidths(text, start, end, widths)
        var sum = 0
        for (i in widths.indices) {
            sum += widths[i].toInt()
        }
        
        return sum + mPadding
    }

    override fun draw(
        canvas: Canvas,
        text: CharSequence,
        start: Int,
        end: Int,
        x: Float,
        top: Int,
        y: Int,
        bottom: Int,
        paint: Paint
    ) {
        canvas.drawText(text, start, end, x, y.toFloat(), paint)
    }
}