Loading AVAssets from Asset Catalogs

AVAsset+Catalog.swift

//
//  AVAsset+Catalog.swift
//  Micro Album
//
//  Created by Fabian Canas on 5/28/19.
//  Copyright © 2019 Fabian Canas. All rights reserved.
//

import AVFoundation
import MobileCoreServices
import UIKit

fileprivate let AssetCache = NSCache<NSString, AVAsset>()

extension AVAsset {

    /// This method looks in in-memory and on-disk caches for an AVAsset with
    /// the specified name. If a matching AVAsset is not already in the cache,
    /// this method locates and loads the video data from disk or from an
    /// asset catalog, and then caches and returns the resulting object.
    ///
    /// - Parameter name: The name of the video asset
    /// - Returns: The video asset for the specified asset name, or nil if the
    ///            method could not find the specified image.
    class func named(_ name: String) -> AVAsset? {

        if let avAsset = AssetCache.object(forKey: name as NSString) {
            return avAsset
        }

        // NSDataAsset lets us have arbitrary data in Asset Catalogs
        guard let dataAsset = NSDataAsset(name: name) else {
            return nil
        }

        let temporaryFilename = "avasset-\(name.addingPercentEncoding(withAllowedCharacters: .urlPathAllowed) ?? ProcessInfo().globallyUniqueString)"

        let cfExtension = UTTypeCopyPreferredTagWithClass(dataAsset.typeIdentifier as CFString, kUTTagClassFilenameExtension)?.takeRetainedValue()
        guard let fileExtension = cfExtension as String? else {
            // AVAsset is picky about the file extension when dealing with local
            // files. If the extension doesn't match what's expected, it's not
            // worth making the asset.
            return nil
        }

        let fileManager = FileManager.default

        let url = fileManager.temporaryDirectory.appendingPathComponent(temporaryFilename).appendingPathExtension(fileExtension)

        if !fileManager.fileExists(atPath: url.path) {
            do {
                try dataAsset.data.write(to: url, options: .atomicWrite)
            } catch {
                return nil
            }
        }

        let avAsset = AVAsset(url: url)
        AssetCache.setObject(avAsset, forKey: name as NSString)

        return avAsset
    }
}