import UIKit
import Photos

class CollectionViewController: UICollectionViewController {
    
    ///取得的资源结果，用了存放的PHAsset
    var assetsFetchResults:PHFetchResult<PHAsset>?
    
    ///缩略图大小
    var assetGridThumbnailSize:CGSize!
    
    /// 带缓存的图片管理对象
    var imageManager:PHCachingImageManager!
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        //根据单元格的尺寸计算我们需要的缩略图大小
        let scale = UIScreen.main.scale
        let cellSize = (self.collectionViewLayout as! UICollectionViewFlowLayout).itemSize
        assetGridThumbnailSize = CGSize(width:cellSize.width*scale ,
                                        height:cellSize.height*scale)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //申请权限
        PHPhotoLibrary.requestAuthorization({ (status) in
            if status != .authorized {
                return
            }
            
            //则获取所有资源
            let allPhotosOptions = PHFetchOptions()
            //按照创建时间倒序排列
            allPhotosOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate",
                                                                 ascending: false)]
            //只获取图片
            allPhotosOptions.predicate = NSPredicate(format: "mediaType = %d",
                                                     PHAssetMediaType.image.rawValue)
            self.assetsFetchResults = PHAsset.fetchAssets(with: PHAssetMediaType.image,
                                                     options: allPhotosOptions)
            
            // 初始化和重置缓存
            self.imageManager = PHCachingImageManager()
            self.resetCachedAssets()
            
            //collection view 重新加载数据
            DispatchQueue.main.async{
                self.collectionView?.reloadData()
            }
        })
    }
    
    //重置缓存
    func resetCachedAssets(){
        self.imageManager.stopCachingImagesForAllAssets()
    }
    
    // CollectionView行数
    override func collectionView(_ collectionView: UICollectionView,
                            numberOfItemsInSection section: Int) -> Int {
        return self.assetsFetchResults?.count ?? 0
    }
    
    // 获取单元格
    override func collectionView(_ collectionView: UICollectionView,
                    cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        // storyboard里设计的单元格
        let identify:String = "DesignViewCell"
        // 获取设计的单元格，不需要再动态添加界面元素
        let cell = (self.collectionView?.dequeueReusableCell(
            withReuseIdentifier: identify, for: indexPath))! as UICollectionViewCell
        
        if let asset = self.assetsFetchResults?[indexPath.row] {
            //获取缩略图
            self.imageManager.requestImage(for: asset, targetSize: assetGridThumbnailSize,
                        contentMode: PHImageContentMode.aspectFill,
                        options: nil) { (image, nfo) in
                        (cell.contentView.viewWithTag(1) as! UIImageView).image = image
                        print(image ?? "")
            }
        }
        
        return cell
    }
    
    // 单元格点击响应
    override func collectionView(_ collectionView: UICollectionView,
                                 didSelectItemAt indexPath: IndexPath) {
        let myAsset = self.assetsFetchResults![indexPath.row]
        
        //这里不使用segue跳转（建议用segue跳转）
        let detailViewController = UIStoryboard(name: "Main", bundle: nil)
            .instantiateViewController(withIdentifier: "detail")
            as! ImageDetailViewController
        detailViewController.myAsset = myAsset
        
        // navigationController跳转到detailViewController
        self.navigationController!.pushViewController(detailViewController,
                                                      animated:true)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

import UIKit
import Photos

class ImageDetailViewController: UIViewController {
    //选中的图片资源
    var myAsset:PHAsset!
    //用于显示图片信息
    @IBOutlet weak var textView: UITextView!
    //用于显示原图
    @IBOutlet weak var imageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //获取文件名
        PHImageManager.default().requestImageData(for: myAsset, options: nil,
                                                                 resultHandler: {
                                                                    _, _, _, info in
            self.title = (info!["PHImageFileURLKey"] as! NSURL).lastPathComponent
        })
        
        //获取图片信息
        textView.text = "日期：\(myAsset.creationDate!)\n"
            + "类型：\(myAsset.mediaType.rawValue)\n"
            + "位置：\(String(describing: myAsset.location))\n"
            + "时长：\(myAsset.duration)\n"
        
        //获取原图
        PHImageManager.default().requestImage(for: myAsset,
                         targetSize: PHImageManagerMaximumSize , contentMode: .default,
                         options: nil, resultHandler: {
                            (image, _: [AnyHashable : Any]?) in
                            self.imageView.image = image
        })
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}