navigation-stack/Source/CollectionView/CollectionStackViewController.swift

//
//  CollectionStackViewController.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
fileprivate func < <T: Comparable>(lhs: T?, rhs: T?) -> Bool {
    switch (lhs, rhs) {
    case let (l?, r?):
        return l < r
    case (nil, _?):
        return true
    default:
        return false
    }
}

// MARK: CollectionStackViewController

protocol CollectionStackViewControllerDelegate: class {
    func controllerDidSelected(index: Int)
}

class CollectionStackViewController: UICollectionViewController {
    fileprivate var screens: [UIImage]
    fileprivate let overlay: Float

    weak var delegate: CollectionStackViewControllerDelegate?

    init(images: [UIImage],
         delegate: CollectionStackViewControllerDelegate?,
         overlay: Float,
         scaleRatio: Float,
         scaleValue: Float,
         bgColor: UIColor = UIColor.clear,
         bgView: UIView? = nil,
         decelerationRate: CGFloat) {

        screens = images
        self.delegate = delegate
        self.overlay = overlay

        let layout = CollectionViewStackFlowLayout(itemsCount: images.count, overlay: overlay, scaleRatio: scaleRatio, scale: scaleValue)
        super.init(collectionViewLayout: layout)

        if let collectionView = self.collectionView {
            collectionView.backgroundColor = bgColor
            collectionView.backgroundView = bgView
            collectionView.decelerationRate = UIScrollView.DecelerationRate(rawValue: decelerationRate)
        }
    }

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

    override func viewDidLoad() {
        configureCollectionView()
        scrolltoIndex(screens.count - 1, animated: false, position: .left) // move to end
    }

    override func viewDidAppear(_: Bool) {

        guard let collectionViewLayout = self.collectionViewLayout as? CollectionViewStackFlowLayout else {
            fatalError("wrong collection layout")
        }

        collectionViewLayout.openAnimating = true
        scrolltoIndex(0, animated: true, position: .left) // open animation
    }
}

// MARK: configure

extension CollectionStackViewController {

    fileprivate func configureCollectionView() {
        guard let collectionViewLayout = self.collectionViewLayout as? UICollectionViewFlowLayout else {
            fatalError("wrong collection layout")
        }

        collectionViewLayout.scrollDirection = .horizontal
        collectionView?.showsHorizontalScrollIndicator = false
        collectionView?.register(CollectionViewStackCell.self, forCellWithReuseIdentifier: String(describing: CollectionViewStackCell.self))
    }
}

// MARK: CollectionViewDataSource

extension CollectionStackViewController {

    override func collectionView(_: UICollectionView, numberOfItemsInSection _: Int) -> Int {
        return screens.count
    }

    override func collectionView(_: UICollectionView,
                                 willDisplay cell: UICollectionViewCell,
                                 forItemAt indexPath: IndexPath) {

        if let cell = cell as? CollectionViewStackCell {
            cell.imageView?.image = screens[(indexPath as NSIndexPath).row]
        }
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: String(describing: CollectionViewStackCell.self),
                                                      for: indexPath)
        return cell
    }

    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let currentCell = collectionView.cellForItem(at: indexPath) else {
            return
        }

        // move cells
        UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseIn,
                       animations: { () -> Void in
                           for cell in self.collectionView!.visibleCells where cell != currentCell {
                               let row = (self.collectionView?.indexPath(for: cell) as NSIndexPath?)?.row
                               let xPosition = row < (indexPath as NSIndexPath).row ? cell.center.x - self.view.bounds.size.width * 2
                                   : cell.center.x + self.view.bounds.size.width * 2

                               cell.center = CGPoint(x: xPosition, y: cell.center.y)
                           }
        }, completion: nil)

        // move to center current cell
        UIView.animate(withDuration: 0.2, delay: 0.2, options: .curveEaseOut,
                       animations: { () -> Void in
                           let offset = collectionView.contentOffset.x - (self.view.bounds.size.width - collectionView.bounds.size.width * CGFloat(self.overlay)) * CGFloat((indexPath as NSIndexPath).row)
                           currentCell.center = CGPoint(x: (currentCell.center.x + offset), y: currentCell.center.y)
        }, completion: nil)

        // scale current cell
        UIView.animate(withDuration: 0.2, delay: 0.6, options: .curveEaseOut, animations: { () -> Void in
            let scale = CGAffineTransform(scaleX: 1, y: 1)
            currentCell.transform = scale
            currentCell.alpha = 1

        }) { (_) -> Void in
            DispatchQueue.main.async(execute: { () -> Void in
                self.delegate?.controllerDidSelected(index: (indexPath as NSIndexPath).row)
                self.dismiss(animated: false, completion: nil)
            })
        }
    }
}

// MARK: UICollectionViewDelegateFlowLayout

extension CollectionStackViewController: UICollectionViewDelegateFlowLayout {

    func collectionView(_: UICollectionView, layout _: UICollectionViewLayout, sizeForItemAt _: IndexPath) -> CGSize {
        return view.bounds.size
    }

    func collectionView(_ collectionView: UICollectionView, layout _: UICollectionViewLayout, minimumLineSpacingForSectionAt _: NSInteger) -> CGFloat {
        return -collectionView.bounds.size.width * CGFloat(overlay)
    }
}

// MARK: Additional helpers

extension CollectionStackViewController {

    fileprivate func scrolltoIndex(_ index: Int, animated: Bool, position: UICollectionView.ScrollPosition) {
        let indexPath = IndexPath(item: index, section: 0)
        collectionView?.scrollToItem(at: indexPath, at: position, animated: animated)
    }
}