Switch to async logic

ios/App/Shared/util/LibraryItemDownloadSession.swift

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+//
+//  LibraryItemDownloadSession.swift
+//  App
+//
+//  Created by Ron Heft on 8/2/22.
+//
+
+import Foundation
+
+enum LibraryItemDownloadError: String, Error {
+    case noTracks = "No tracks on library item"
+    case noMetadata = "No metadata for track, unable to download"
+    case failedDownload = "Failed to download item"
+}
+
+class LibraryItemDownloadSession {
+    
+    let item: LibraryItem
+    
+    private let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
+    
+    init(_ item: LibraryItem) {
+        self.item = item
+    }
+    
+    public func startDownload() async throws -> LocalLibraryItem {
+        guard let tracks = item.media.tracks else {
+            throw LibraryItemDownloadError.noTracks
+        }
+        
+        return try await withThrowingTaskGroup(of: LocalFile.self, returning: LocalLibraryItem.self) { group in
+            for (position, track) in tracks.enumerated() {
+                group.addTask { try await self.startLibraryItemTrackDownload(item: self.item, position: position, track: track) }
+            }
+            
+            var files = [LocalFile]()
+            for try await file in group {
+                files.append(file)
+            }
+            
+            return LocalLibraryItem(self.item, localUrl: self.documentsDirectory, server: Store.serverConfig!, files: files)
+        }
+    }
+    
+    private func startLibraryItemTrackDownload(item: LibraryItem, position: Int, track: AudioTrack) async throws -> LocalFile {
+        NSLog("TRACK \(track.contentUrl!)")
+        
+        // If we don't name metadata, then we can't proceed
+        guard let filename = track.metadata?.filename else {
+            throw LibraryItemDownloadError.noMetadata
+        }
+        
+        let serverUrl = urlForTrack(item: item, track: track)
+        let itemDirectory = createLibraryItemFileDirectory(item: item)
+        let localUrl = itemDirectory.appendingPathComponent("\(filename)")
+        
+        try await downloadFile(serverUrl: serverUrl, localUrl: localUrl)
+        return LocalFile(item.id, filename, track.mimeType, localUrl)
+    }
+    
+    private func createLibraryItemFileDirectory(item: LibraryItem) -> URL {
+        let itemDirectory = documentsDirectory.appendingPathComponent("\(item.id)")
+        
+        NSLog("ITEM DIR \(itemDirectory)")
+        
+        // Create library item directory
+        do {
+            try FileManager.default.createDirectory(at: itemDirectory, withIntermediateDirectories: true)
+        } catch {
+            NSLog("Failed to CREATE LI DIRECTORY \(error)")
+        }
+        
+        return itemDirectory
+    }
+    
+    private func urlForTrack(item: LibraryItem, track: AudioTrack) -> URL {
+        // filename needs to be encoded otherwise would just use contentUrl
+        let filenameEncoded = track.metadata?.filename.addingPercentEncoding(withAllowedCharacters: NSCharacterSet.urlQueryAllowed)
+        let urlstr = "\(Store.serverConfig!.address)/s/item/\(item.id)/\(filenameEncoded ?? "")?token=\(Store.serverConfig!.token)"
+        return URL(string: urlstr)!
+    }
+    
+    private func downloadFile(serverUrl: URL, localUrl: URL) async throws {
+        return try await withCheckedThrowingContinuation { continuation in
+            let downloadTask = URLSession.shared.downloadTask(with: serverUrl) { urlOrNil, responseOrNil, errorOrNil in
+                guard let tempUrl = urlOrNil else {
+                    continuation.resume(throwing: errorOrNil!)
+                    return
+                }
+                
+                do {
+                    try FileManager.default.moveItem(at: tempUrl, to: localUrl)
+                    continuation.resume()
+                } catch {
+                    continuation.resume(throwing: error)
+                }
+            }
+            downloadTask.resume()
+        }
+    }
+    
+}