import Combine
import Foundation
import UIKit

final class FileMiddleware {
    static let shared = FileMiddleware()
    private var downloadingMessageIDs = ThreadSafeSet<String>()

    func middleware(state _: AppState, action: AppAction) -> AnyPublisher<AppAction, Never> {
        switch action {
        case .conversationAction(.messagesUpdated(let messages)):
            return Future { [weak self] promise in
                guard let wSelf = self else {
                    promise(.success(.empty))
                    return
                }
                for message in messages where message.attachmentRemotePath != nil && message.attachmentLocalPath == nil {
                    if wSelf.downloadingMessageIDs.contains(message.id) {
                        continue
                    }
                    wSelf.downloadingMessageIDs.insert(message.id)
                    DispatchQueue.main.async {
                        // swiftlint:disable:next force_unwrapping
                        store.dispatch(.fileAction(.downloadAttachmentFile(id: message.id, attachmentRemotePath: message.attachmentRemotePath!)))
                    }
                }
                promise(.success(.empty))
            }.eraseToAnyPublisher()

        case .fileAction(.downloadAttachmentFile(let id, let attachmentRemotePath)):
            return Future { promise in
                let localUrl = FileProcessing.fileFolder.appendingPathComponent(id).appendingPathExtension(attachmentRemotePath.pathExtension)
                DownloadManager.shared.enqueueDownload(from: attachmentRemotePath, to: localUrl) { error in
                    DispatchQueue.main.async {
                        if let error {
                            store.dispatch(.fileAction(.downloadingAttachmentFileFailed(id: id, reason: error.localizedDescription)))
                        } else {
                            store.dispatch(.fileAction(.attachmentFileDownloaded(id: id, localUrl: localUrl)))
                        }
                    }
                }
                promise(.success(.empty))
            }.eraseToAnyPublisher()

        case .fileAction(.attachmentFileDownloaded(let id, let localUrl)):
            return Future { [weak self] promise in
                self?.downloadingMessageIDs.remove(id)
                promise(.success(.fileAction(.createAttachmentThumbnail(id: id, localUrl: localUrl))))
            }
            .eraseToAnyPublisher()

        case .fileAction(.createAttachmentThumbnail(let id, let localUrl)):
            return Future { [weak self] promise in
                if let thumbnailUrl = FileProcessing.shared.createThumbnail(localUrl: localUrl) {
                    self?.downloadingMessageIDs.remove(id)
                    promise(.success(.fileAction(.attachmentThumbnailCreated(id: id, thumbnailUrl: thumbnailUrl))))
                } else {
                    self?.downloadingMessageIDs.remove(id)
                    promise(.success(.empty))
                }
            }
            .eraseToAnyPublisher()

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