/*
 * Copyright (c) 2019 Hemanth Savarala.
 *
 * Licensed under the GNU General Public License v3
 *
 * This is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by
 *  the Free Software Foundation either version 3 of the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 */

package code.name.monkey.retromusic.transform

import android.view.View
import androidx.viewpager.widget.ViewPager
import kotlin.math.abs
import kotlin.math.max

/**
 * @author Hemanth S (h4h13).
 */

class NormalPageTransformer : ViewPager.PageTransformer {

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

        when {
            position < -1 -> { // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.alpha = 1f
                view.scaleY = 0.7f
            }
            position <= 1 -> { // [-1,1]
                // Modify the default slide transition to shrink the page as well
                val scaleFactor = max(MIN_SCALE, 1 - 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.setAlpha(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 = 1f
                view.scaleY = 0.7f
            }
        }
    }

    companion object {
        private const val MIN_SCALE = 0.85f
        private const val MIN_ALPHA = 0.5f
    }
}