/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    AssetViewController's implementation of the AssetTransitioning protocol used as the handshaking mechanism when transitioning.

*/

import UIKit

import Photos

import AVKit

extension AssetViewController: AssetTransitioning {

    func itemsForTransition(context: UIViewControllerContextTransitioning) -> Array<AssetTransitionItem> {

        guard let collectionView = self.collectionView else { return [] }

        var indexPaths = collectionView.indexPathsForVisibleItems

        if context.isInteractive {

            if let indexPath = collectionView.indexPathForItem(at: collectionView.panGestureRecognizer.location(in: collectionView)) {

                indexPaths = [indexPath]

            }

        }

        return indexPaths.map({ (indexPath: IndexPath) -> AssetTransitionItem in

            let cell = collectionView.cellForItem(at: indexPath) as! AssetCell

            let asset = self.fetchResult.object(at: indexPath.item)

            let initialFrame: CGRect

            switch self.layoutStyle {

            case .oneUp:

                let boundingRect = cell.imageView.convert(cell.imageView.bounds, to: nil)

                let aspectRatio = CGSize(width: asset.pixelWidth, height: asset.pixelHeight)

                initialFrame = AVMakeRect(aspectRatio: aspectRatio, insideRect: boundingRect)

            case .grid:

                initialFrame = cell.convert(cell.bounds, to: nil)

            }

            return AssetTransitionItem(initialFrame: initialFrame, image: cell.imageView.image!, indexPath: indexPath, asset: asset)

        })

    }

    func targetFrame(transitionItem item: AssetTransitionItem) -> CGRect? {

        guard let collectionView = self.collectionView else { return nil }

        switch self.layoutStyle {

        case .oneUp:

            if item.asset.localIdentifier == self.transitioningAsset?.localIdentifier {

                let boundingRect = self.view.convert(self.view.bounds, to: nil)

                let aspectRatio = CGSize(width: item.asset.pixelWidth, height: item.asset.pixelHeight)

                return AVMakeRect(aspectRatio: aspectRatio, insideRect: boundingRect)

            }

        case .grid:

            if !collectionView.indexPathsForVisibleItems.contains(item.indexPath) {

                collectionView.scrollToItem(at: item.indexPath, at: .centeredVertically, animated: false)

                collectionView.layoutIfNeeded()

            }

            if let cell = collectionView.cellForItem(at: item.indexPath) as? AssetCell {

                if cell.assetIdentifier == item.asset.localIdentifier {

                    return cell.convert(cell.bounds, to: nil)

                }

            }

        }

        return nil

    }

    func willTransition(fromController: UIViewController, toController: UIViewController, items: Array<AssetTransitionItem>) {

        guard let collectionView = self.collectionView else { return }

        switch self.layoutStyle {

        case .oneUp:

            collectionView.alpha = 0.0

            collectionView.panGestureRecognizer.isEnabled = false

            if self == toController {

                if let asset = items.last?.asset {

                    let indexPath = IndexPath(row: fetchResult.index(of: asset), section: 0)

                    collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: false)

                }

            }

        case .grid:

            let options = PHImageRequestOptions()

            options.deliveryMode = .opportunistic

            options.isNetworkAccessAllowed = true

            for item in items {

                collectionView.cellForItem(at: item.indexPath)?.alpha = 0.0

                // Update the image resolution

                if self == fromController {

                    self.imageManager.requestImage(for: item.asset, targetSize: item.targetFrame!.size, contentMode: .aspectFit, options: options, resultHandler: { [weak item] (result, _) in

                        if let image = result {

                            item?.image = image

                        }

                    })

                }

            }

        }

    }

    func didTransition(fromController: UIViewController, toController: UIViewController, items: Array<AssetTransitionItem>) {

        guard let collectionView = self.collectionView else { return }

        switch self.layoutStyle {

        case .oneUp:

            collectionView.alpha = 1.0

            collectionView.panGestureRecognizer.isEnabled = true

        case .grid:

            for item in items {

                collectionView.cellForItem(at: item.indexPath)?.alpha = 1.0

            }

        }

    }

}