//
//  CollectionViewStackFlowLayout.swift
//  NavigationStackDemo
//
// Copyright (c) 26/02/16 Ramotion Inc. (http://ramotion.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import UIKit

// MARK: CollectionViewStackFlowLayout

class CollectionViewStackFlowLayout: UICollectionViewFlowLayout {

    let itemsCount: Int
    let overlay: Float // from 0 to 1

    let maxScale: Float
    let scaleRatio: Float

    var additionScale = 1.0
    var openAnimating = false

    var dxOffset: Float = 0

    init(itemsCount: Int, overlay: Float, scaleRatio: Float, scale: Float) {
        self.itemsCount = itemsCount
        self.overlay = overlay
        self.scaleRatio = scaleRatio
        maxScale = scale
        super.init()
    }

    required init?(coder _: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

extension CollectionViewStackFlowLayout {

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let items = NSArray(array: super.layoutAttributesForElements(in: rect)!, copyItems: true)
        var headerAttributes: UICollectionViewLayoutAttributes?

        items.enumerateObjects({ (object, _, _) -> Void in
            let attributes = object as! UICollectionViewLayoutAttributes

            if attributes.representedElementKind == UICollectionView.elementKindSectionHeader {
                headerAttributes = attributes
            } else {
                self.updateCellAttributes(attributes, headerAttributes: headerAttributes)
            }
        })
        return items as? [UICollectionViewLayoutAttributes]
    }

    func updateCellAttributes(_ attributes: UICollectionViewLayoutAttributes, headerAttributes _: UICollectionViewLayoutAttributes?) {

        guard let collectionView = self.collectionView else {
            return
        }
        let itemWidth = collectionView.bounds.size.width - collectionView.bounds.size.width * CGFloat(overlay)
        let allWidth = itemWidth * CGFloat(itemsCount - 1)

        // set contentOffset range
        let contentOffsetX = min(max(0, collectionView.contentOffset.x), allWidth)

        let scale = transformScale(attributes, allWidth: allWidth, offset: contentOffsetX)
        let move = transformMove(attributes, itemWidth: itemWidth, offset: contentOffsetX)
        attributes.transform = scale.concatenating(move)
        attributes.alpha = calculateAlpha(attributes, itemWidth: itemWidth, offset: contentOffsetX)

        if additionScale > 0 && openAnimating {
            additionScale -= 0.02
            additionScale = additionScale < 0 ? 0 : additionScale
        }
        attributes.zIndex = (attributes.indexPath as NSIndexPath).row
    }

    override func shouldInvalidateLayout(forBoundsChange _: CGRect) -> Bool {
        return true
    }
}

// MARK: helpers

extension CollectionViewStackFlowLayout {

    fileprivate func transformScale(_ attributes: UICollectionViewLayoutAttributes,
                                    allWidth: CGFloat,
                                    offset: CGFloat) -> CGAffineTransform {
        var maximum = CGFloat(maxScale) - CGFloat(itemsCount - (attributes.indexPath as NSIndexPath).row) / CGFloat(scaleRatio)
        maximum += CGFloat(1.0 - maximum) * CGFloat(additionScale)

        var minimum = CGFloat(maxScale - 0.1) - CGFloat(itemsCount - (attributes.indexPath as NSIndexPath).row) / CGFloat(scaleRatio)
        minimum += CGFloat(1.0 - minimum) * CGFloat(additionScale)

        var currentScale = (maximum + minimum) - (minimum + offset / (allWidth / (maximum - minimum)))
        currentScale = max(min(maximum, currentScale), minimum)
        return CGAffineTransform(scaleX: currentScale, y: currentScale)
    }

    fileprivate func transformMove(_ attributes: UICollectionViewLayoutAttributes,
                                   itemWidth: CGFloat,
                                   offset: CGFloat) -> CGAffineTransform {
        var currentContentOffsetX = offset - itemWidth * CGFloat((attributes.indexPath as NSIndexPath).row)
        currentContentOffsetX = min(max(currentContentOffsetX, 0), itemWidth)

        var dx = (currentContentOffsetX / itemWidth)
        if let collectionView = self.collectionView {
            dx *= collectionView.bounds.size.width / 8.0
        }
        dx = currentContentOffsetX - dx

        return CGAffineTransform(translationX: dx, y: 0)
    }

    fileprivate func calculateAlpha(_ attributes: UICollectionViewLayoutAttributes, itemWidth: CGFloat, offset: CGFloat) -> CGFloat {
        var currentContentOffsetX = offset - itemWidth * CGFloat((attributes.indexPath as NSIndexPath).row)
        currentContentOffsetX = min(max(currentContentOffsetX, 0), itemWidth)

        let dx = (currentContentOffsetX / itemWidth)

        return 1.0 - dx
    }
}