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 {
        // MARK: - For incomig attachments
        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(messageId: message.id, attachmentRemotePath: message.attachmentRemotePath!)))
                    }
                }
                promise(.success(.empty))
            }.eraseToAnyPublisher()

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

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

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

        // MARK: - For outgoing sharing
        case .fileAction(.fetchItemsFromGallery):
            return Future<AppAction, Never> { promise in
                let items = FileProcessing.shared.fetchGallery()
                promise(.success(.fileAction(.itemsFromGalleryFetched(items: items))))
            }
            .eraseToAnyPublisher()

        case .fileAction(.itemsFromGalleryFetched(let items)):
            return Future { promise in
                let newItems = FileProcessing.shared.fillGalleryItemsThumbnails(items: items)
                promise(.success(.sharingAction(.galleryItemsUpdated(items: newItems))))
            }
            .eraseToAnyPublisher()

        case .fileAction(.copyGalleryItemsForUploading(let items)):
            return Future { promise in
                let ids = FileProcessing.shared.copyGalleryItemsForUploading(items: items)
                promise(.success(.fileAction(.galleryItemsCopiedForUploading(newMessageIds: ids.map { $0.0 }, localNames: ids.map { $0.1 }))))
            }
            .eraseToAnyPublisher()

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