[TIL] 2021.02.01

    let photoAurhorizationStatus = PHPhotoLibrary.authorizationStatus()
    
    switch photoAurhorizationStatus  {
    case .authorized :
        print("접근 허가됨")
        self.requestCollection()
    case .denied :
        print("접근 불허")
    case .notDetermined:
        print("아직 응답하지 않음")
        PHPhotoLibrary.requestAuthorization( { (status) in
            switch status {
            case .authorized:
                print("사용자가 허용함")
                self.requestCollection()
                DispatchQueue.main.async {
                    self.collectionView.reloadData()
                }
            case .denied:
                print("사용자가 불허함")
            default: break
            }
        })
    case .restricted:
        print("접근 제한")
    case .limited:
        print("접근 어쩌구")
    @unknown default:
        print("접근 오류")
    }

    import Photos 

    var fetchResult: PHFetchResult<PHAsset>!
    var imageManager: PHCachingImageManager = PHCachingImageManager()

    let cameraRoll: PHFetchResult<PHAssetCollection> = PHAssetCollection.fetchAssetCollections(with: .smartAlbum, subtype: .smartAlbumUserLibrary, options: nil)
    guard let cameraRollCollection = cameraRoll.firstObject else {
        return
    }
    
    let fetchOptions = PHFetchOptions()
    // 최신 순으로 불러오는 옵션
    fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
    // asset 불러오기
    self.fetchResult = PHAsset.fetchAssets(in: cameraRollCollection, options: fetchOptions) 

extension PhotoLibraryViewController:  UICollectionViewDataSource{
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.fetchResult?.count ?? 0
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PhotoLibraryCell", for: indexPath) as? PhotoLibraryCell else { return UICollectionViewCell() }
        
        let asset: PHAsset = fetchResult.object(at: indexPath.item)
        imageManager.requestImage(for: asset, targetSize: CGSize(width: 100, height: 100), contentMode: .aspectFill, options: nil, resultHandler: { image, info in
                cell.updateUI(image)
        })
        
        return cell
    }
}