//
// Swiftfin is subject to the terms of the Mozilla Public
// License, v2.0. If a copy of the MPL was not distributed with this
// file, you can obtain one at https://mozilla.org/MPL/2.0/.
//
// Copyright (c) 2024 Jellyfin & Jellyfin Contributors
//

import Combine
import Foundation
import JellyfinAPI
import OrderedCollections

class ItemEditorViewModel<ItemType: Equatable>: ViewModel, Stateful, Eventful {

    // MARK: - Events

    enum Event: Equatable {
        case updated
        case error(JellyfinAPIError)
    }

    // MARK: - Actions

    enum Action: Equatable {
        case add([ItemType])
        case remove([ItemType])
        case update(BaseItemDto)
    }

    // MARK: BackgroundState

    enum BackgroundState: Hashable {
        case refreshing
    }

    // MARK: - State

    enum State: Hashable {
        case initial
        case error(JellyfinAPIError)
        case updating
    }

    @Published
    var backgroundStates: OrderedSet<BackgroundState> = []

    @Published
    var item: BaseItemDto

    @Published
    var state: State = .initial

    private var task: AnyCancellable?
    private let eventSubject = PassthroughSubject<Event, Never>()

    var events: AnyPublisher<Event, Never> {
        eventSubject.receive(on: RunLoop.main).eraseToAnyPublisher()
    }

    // MARK: - Init

    init(item: BaseItemDto) {
        self.item = item
        super.init()
    }

    // MARK: - Respond to Actions

    func respond(to action: Action) -> State {
        switch action {
        case let .add(items):
            task?.cancel()

            task = Task { [weak self] in
                guard let self = self else { return }
                do {
                    await MainActor.run { self.state = .updating }

                    try await self.addComponents(items)

                    await MainActor.run {
                        self.state = .initial
                        self.eventSubject.send(.updated)
                    }
                } catch {
                    let apiError = JellyfinAPIError(error.localizedDescription)
                    await MainActor.run {
                        self.state = .error(apiError)
                        self.eventSubject.send(.error(apiError))
                    }
                }
            }.asAnyCancellable()

            return state

        case let .remove(items):
            task?.cancel()

            task = Task { [weak self] in
                guard let self = self else { return }
                do {
                    await MainActor.run { self.state = .updating }

                    try await self.removeComponents(items)

                    await MainActor.run {
                        self.state = .initial
                        self.eventSubject.send(.updated)
                    }
                } catch {
                    let apiError = JellyfinAPIError(error.localizedDescription)
                    await MainActor.run {
                        self.state = .error(apiError)
                        self.eventSubject.send(.error(apiError))
                    }
                }
            }.asAnyCancellable()

            return state

        case let .update(newItem):
            task?.cancel()

            task = Task { [weak self] in
                guard let self = self else { return }
                do {
                    await MainActor.run { self.state = .updating }

                    try await self.updateItem(newItem)

                    await MainActor.run {
                        self.state = .initial
                        self.eventSubject.send(.updated)
                    }
                } catch {
                    let apiError = JellyfinAPIError(error.localizedDescription)
                    await MainActor.run {
                        self.state = .error(apiError)
                        self.eventSubject.send(.error(apiError))
                    }
                }
            }.asAnyCancellable()

            return state
        }
    }

    // MARK: - Save Updated Item to Server

    func updateItem(_ newItem: BaseItemDto, refresh: Bool = false) async throws {
        guard let itemId = item.id else { return }

        let request = Paths.updateItem(itemID: itemId, newItem)
        _ = try await userSession.client.send(request)

        if refresh {
            try await refreshItem()
        }

        await MainActor.run {
            Notifications[.itemMetadataDidChange].post(object: newItem)
        }
    }

    // MARK: - Refresh Item

    private func refreshItem() async throws {
        guard let itemId = item.id else { return }

        await MainActor.run {
            _ = backgroundStates.append(.refreshing)
        }

        let request = Paths.getItem(userID: userSession.user.id, itemID: itemId)
        let response = try await userSession.client.send(request)

        await MainActor.run {
            self.item = response.value
            _ = backgroundStates.remove(.refreshing)
        }
    }

    // MARK: - Add Items (To be overridden)

    func addComponents(_ items: [ItemType]) async throws {
        fatalError("This method should be overridden in subclasses")
    }

    // MARK: - Remove Items (To be overridden)

    func removeComponents(_ items: [ItemType]) async throws {
        fatalError("This method should be overridden in subclasses")
    }
}