import android.widget.TextView

/**
* sets an alpha on the lines after the Nth line, this could be useful for when animating a TextView to get smnaller and have less lines
* alpha: the desired alpha
* onLinesAfter: all lines after this line will have the color set on them (1 based index, i.e first line is 1 not 0)
* forceColor: by default will use the color already set on the TextView, but you can over ride the color if needed
* return: the spannable used, in case you need to remove it later
*/
fun TextView.alphaOnLinesAfterN(alpha: Float, onLinesAfter: Int, @ColorInt forceColor: Int = this.currentTextColor): Spannable? {

    layout?.let {
        if (it.lineCount > onLinesAfter) {

            val newColor = Color.argb((alpha * 255).toInt(), forceColor.red, forceColor.green, forceColor.blue)
            var sp = text as Spannable

            sp.setSpan(ForegroundColorSpan(newColor), it.getLineStart(onLinesAfter), length(), Spannable.SPAN_INCLUSIVE_INCLUSIVE)
            text = sp
            return sp
        }
    }
    return null
}