ViewPager2 OnPageChangeCallback that tracks the percentage visibility for each page

PercentPageChangeCallback.kt

object : ViewPager2.OnPageChangeCallback() {
    private var settledOnPage = 0
    private var idle = true

    val percentages = MutableList(adapter!!.itemCount) { 0f }
            .apply { set(0, 1f) }

    override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {
        Timber.i("${1f - positionOffset} of page ${position + 1} is visible")

        if (!idle && settledOnPage < position + 1) {
            Timber.i("Dragging left $positionOffset, ${1f - positionOffset} of index ${position} is visible")

            percentages[position] = 1f - positionOffset
            if (position < percentages.size - 1) percentages[position + 1] = positionOffset
            if (positionOffset == 0f && position > 1) percentages[position - 1] = 0f

            Timber.i(percentages.joinToString(separator = " ") { "[%.2f]".format(it) })

            notifyObservers(percentages)
        } else if (settledOnPage == position + 1) {
            Timber.i("Dragging right $positionOffset")

            percentages[position + 1] = positionOffset
            percentages[position] = 1f - positionOffset
            if (positionOffset == 0f && position < percentages.size - 1) percentages[position + 1] = 0f

            Timber.i(percentages.joinToString(separator = " ") { "[%.2f]".format(it) })

            notifyObservers(percentages)
        }

        notifyObservers(percentages)
    }

    override fun onPageScrollStateChanged(state: Int) {
        when (state) {
            ViewPager2.SCROLL_STATE_IDLE -> {
                settledOnPage = currentItem
                idle = true
                Timber.i("Idle on $settledOnPage")
            }
            ViewPager2.SCROLL_STATE_DRAGGING -> { idle = false }
            ViewPager2.SCROLL_STATE_SETTLING -> { idle = false }
        }
    }
}