Kotlin port of the original ZoomOutPageTransformer class, found in Android SDK documentation

ZoomOutPageTransformer.kt

/*
 * Copyright (C) 2018 Olmo Gallegos Hernández.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.appandweb.weevento.ui.adapter

import android.support.v4.view.ViewPager
import android.view.View

/**
 * This is a line-to-line port to Kotlin for the ZoomOutPageTransformer class, found here:
 * https://developer.android.com/training/animation/screen-slide.html
 * I am not the owner of the original code
 */
class ZoomOutPageTransformer : ViewPager.PageTransformer {
    val MIN_SCALE = 0.85f
    val MIN_ALPHA = 0.5f

    override fun transformPage(view: View?, position: Float) {
        val pageWidth = view?.width ?: 0
        val pageHeight = view?.height ?: 0

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view?.alpha = 0f
        } else if (position <= 1) { // [-1, 1]
            val scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position))
            val vertMargin = pageHeight * (1 - scaleFactor) / 2
            val horzMargin = pageWidth * (1 - scaleFactor) / 2

            if (position < 0) {
                view?.translationX = horzMargin - vertMargin / 2
            } else {
                view?.translationX = -horzMargin + vertMargin / 2
            }

            // Scale the page down (between MIN_SCALE and 1)
            view?.scaleX = scaleFactor
            view?.scaleY = scaleFactor

            // Fade the page relative to its size.
            view?.alpha = MIN_ALPHA +
                    (scaleFactor - MIN_SCALE) /
                            (1 - MIN_SCALE) * (1 - MIN_ALPHA)
        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view?.alpha = 0f
        }
    }
}