import Combine
import Foundation
import GRDB

final class DatabaseMiddleware {
    static let shared = DatabaseMiddleware()
    private let database = Database.shared
    private var cancellables: Set<AnyCancellable> = []

    private init() {
        // Database changes
        ValueObservation
            .tracking(Roster.fetchAll)
            .publisher(in: database._db, scheduling: .immediate)
            .sink { _ in
                // Handle completion
            } receiveValue: { rosters in
                DispatchQueue.main.async {
                    store.dispatch(.databaseAction(.storedRostersLoaded(rosters: rosters)))
                }
            }
            .store(in: &cancellables)
        ValueObservation
            .tracking(Chat.fetchAll)
            .publisher(in: database._db, scheduling: .immediate)
            .sink { _ in
                // Handle completion
            } receiveValue: { chats in
                DispatchQueue.main.async {
                    store.dispatch(.databaseAction(.storedChatsLoaded(chats: chats)))
                }
            }
            .store(in: &cancellables)
    }

    func middleware(state _: AppState, action: AppAction) -> AnyPublisher<AppAction, Never> {
        switch action {
        case .startAction(.loadStoredAccounts):
            return Future<AppAction, Never> { promise in
                Task(priority: .background) { [weak self] in
                    guard let database = self?.database else {
                        promise(.success(.databaseAction(.loadingStoredAccountsFailed)))
                        return
                    }
                    do {
                        try database._db.read { db in
                            let accounts = try Account.fetchAll(db)
                            promise(.success(.databaseAction(.storedAccountsLoaded(accounts: accounts))))
                        }
                    } catch {
                        promise(.success(.databaseAction(.loadingStoredAccountsFailed)))
                    }
                }
            }
            .eraseToAnyPublisher()

        case .accountsAction(.makeAccountPermanent(let account)):
            return Future<AppAction, Never> { promise in
                Task(priority: .background) { [weak self] in
                    guard let database = self?.database else {
                        promise(.success(.databaseAction(.updateAccountFailed)))
                        return
                    }
                    do {
                        try database._db.write { db in
                            // make permanent and store to database
                            var acc = account
                            acc.isTemp = false
                            try acc.insert(db)

                            // Re-Fetch all accounts
                            let accounts = try Account.fetchAll(db)

                            // Use the accounts
                            promise(.success(.databaseAction(.storedAccountsLoaded(accounts: accounts))))
                        }
                    } catch {
                        promise(.success(.databaseAction(.updateAccountFailed)))
                    }
                }
            }
            .eraseToAnyPublisher()

        case .rostersAction(.markRosterAsLocallyDeleted(let ownerJID, let contactJID)):
            return Future<AppAction, Never> { promise in
                Task(priority: .background) { [weak self] in
                    guard let database = self?.database else {
                        promise(.success(.rostersAction(.rosterDeletingFailed(reason: L10n.Global.Error.genericDbError))))
                        return
                    }
                    do {
                        _ = try database._db.write { db in
                            try Roster
                                .filter(Column("bareJid") == ownerJID)
                                .filter(Column("contactBareJid") == contactJID)
                                .updateAll(db, Column("locallyDeleted").set(to: true))
                        }
                        promise(.success(.empty))
                    } catch {
                        promise(.success(.rostersAction(.rosterDeletingFailed(reason: L10n.Global.Error.genericDbError))))
                    }
                }
            }
            .eraseToAnyPublisher()

        case .rostersAction(.unmarkRosterAsLocallyDeleted(let ownerJID, let contactJID)):
            return Future<AppAction, Never> { promise in
                Task(priority: .background) { [weak self] in
                    guard let database = self?.database else {
                        promise(.success(.rostersAction(.rosterDeletingFailed(reason: L10n.Global.Error.genericDbError))))
                        return
                    }
                    do {
                        _ = try database._db.write { db in
                            try Roster
                                .filter(Column("bareJid") == ownerJID)
                                .filter(Column("contactBareJid") == contactJID)
                                .updateAll(db, Column("locallyDeleted").set(to: false))
                        }
                        promise(.success(.empty))
                    } catch {
                        promise(.success(.rostersAction(.rosterDeletingFailed(reason: L10n.Global.Error.genericDbError))))
                    }
                }
            }
            .eraseToAnyPublisher()

        case .chatsAction(.createNewChat(let accountJid, let participantJid)):
            return Future<AppAction, Never> { promise in
                Task(priority: .background) { [weak self] in
                    guard let database = self?.database else {
                        promise(.success(.chatsAction(.chatCreationFailed(reason: L10n.Global.Error.genericDbError))))
                        return
                    }
                    do {
                        try database._db.write { db in
                            let chat = Chat(
                                id: UUID().uuidString,
                                account: accountJid,
                                participant: participantJid,
                                type: .chat
                            )
                            try chat.insert(db)
                            promise(.success(.chatsAction(.chatCreated(chat: chat))))
                        }
                    } catch {
                        promise(.success(.chatsAction(.chatCreationFailed(reason: L10n.Global.Error.genericDbError))))
                    }
                }
            }
            .eraseToAnyPublisher()

        case .xmppAction(.xmppMessageReceived(let message)):
            if message.type != .chat {
                return Empty().eraseToAnyPublisher()
            }
            // TODO: Store msg here!
            return Empty().eraseToAnyPublisher()

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