another.im-ios/ConversationsClassic/AppCore/Middlewares/FileMiddleware.swift

import Combine
import Foundation
import UIKit

final class FileMiddleware {
    static let shared = FileMiddleware()
    private var downloader = DownloadManager()

    func middleware(state _: AppState, action: AppAction) -> AnyPublisher<AppAction, Never> {
        switch action {
        case .conversationAction(.attachmentsUpdated(let attachments)):
            DispatchQueue.global(qos: .background).async {
                for attachment in attachments where attachment.localPath == nil {
                    if let remotePath = attachment.remotePath {
                        let localUrl = self.fileFolder.appendingPathComponent(attachment.id)
                        self.downloader.download(from: remotePath, to: localUrl) { error in
                            if error == nil {
                                DispatchQueue.main.async {
                                    store.dispatch(.fileAction(.attachmentFileDownloaded(id: attachment.id, localUrl: localUrl)))
                                }
                            }
                        }
                    }
                }
            }
            return Empty().eraseToAnyPublisher()

        case .fileAction(.attachmentFileDownloaded(let id, let localUrl)):
            DispatchQueue.global(qos: .background).async {
                guard let attachment = store.state.conversationsState.currentAttachments.first(where: { $0.id == id }) else { return }
                switch attachment.type {
                case .image:
                    if let data = try? Data(contentsOf: localUrl), let image = UIImage(data: data) {
                        image.scaleAndCropImage(toExampleSize: CGSizeMake(Const.attachmentPreviewSize, Const.attachmentPreviewSize)) { img in
                            if let img = img, let data = img.jpegData(compressionQuality: 1.0) {
                                let thumbnailUrl = self.fileFolder.appendingPathComponent("\(id)_thumbnail.jpg")
                                do {
                                    try data.write(to: thumbnailUrl)
                                    DispatchQueue.main.async {
                                        store.dispatch(.fileAction(.attachmentThumbnailCreated(id: id, thumbnailUrl: thumbnailUrl)))
                                    }
                                } catch {
                                    print("Error writing thumbnail: \(error)")
                                }
                            }
                        }
                    }

                case .movie:
                    // self.downloadAndMakeThumbnail(for: attachment)
                    break

                default:
                    break
                }
            }
            return Empty().eraseToAnyPublisher()

        default:
            return Empty().eraseToAnyPublisher()
        }
    }
}

private extension FileMiddleware {
    var fileFolder: URL {
        // swiftlint:disable:next force_unwrapping
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        return documentsURL.appendingPathComponent(Const.fileFolder)
    }
}

private final class DownloadManager {
    private let urlSession: URLSession

    init() {
        let configuration = URLSessionConfiguration.default
        urlSession = URLSession(configuration: configuration)
    }

    func download(from url: URL, to localUrl: URL, completion: @escaping (Error?) -> Void) {
        let task = urlSession.downloadTask(with: url) { tempLocalUrl, _, error in
            if let tempLocalUrl = tempLocalUrl, error == nil {
                do {
                    try FileManager.default.copyItem(at: tempLocalUrl, to: localUrl)
                    completion(nil)
                } catch let writeError {
                    completion(writeError)
                }
            } else {
                completion(error)
            }
        }
        task.resume()
    }
}