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

DepthPageTransformer.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 DepthPageTransformer class, found here:
 * https://developer.android.com/training/animation/screen-slide.html
 * I am not the owner of the original code
 */
class DepthPageTransformer : ViewPager.PageTransformer {
    val MIN_SCALE = 0.5f

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

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view?.alpha = 0f
        } else if (position <= 0) { // [-1,0]
            // Use the default slide transition when moving to the left page
            view?.apply {
                alpha = 1f
                translationX = 0f
                scaleX = 1f
                scaleY = 1f
            }
        } else if (position <= 1) { // (0,1]
            view?.apply {
                // Fade the page out.
                alpha = 1 - position

                // Counteract the default slide transition
                translationX = pageWidth * -position

                // Scale the page down (between MIN_SCALE and 1)
                val scaleFactor = MIN_SCALE +
                        (1 - MIN_SCALE) * (1 - Math.abs(position))
                scaleX = scaleFactor
                scaleY = scaleFactor
            }
        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view?.alpha = 0f
        }
    }
}