//
//  ShareViewModel.swift
//  MastodonShareAction
//
//  Created by MainasuK Cirno on 2021-7-16.
//

import os.log
import Foundation
import Combine
import CoreData
import CoreDataStack
import MastodonSDK
import MastodonUI
import SwiftUI
import UniformTypeIdentifiers

final class ShareViewModel {

    let logger = Logger(subsystem: "ShareViewModel", category: "logic")

    var disposeBag = Set<AnyCancellable>()

    static let composeContentLimit: Int = 500

    // input
    private var coreDataStack: CoreDataStack?
    var managedObjectContext: NSManagedObjectContext?
    var inputItems = CurrentValueSubject<[NSExtensionItem], Never>([])
    let viewDidAppear = CurrentValueSubject<Bool, Never>(false)
    let traitCollectionDidChangePublisher = CurrentValueSubject<Void, Never>(Void())      // use CurrentValueSubject to make initial event emit
    let selectedStatusVisibility = CurrentValueSubject<ComposeToolbarView.VisibilitySelectionType, Never>(.public)

    // output
    let authentication = CurrentValueSubject<Result<MastodonAuthentication, Error>?, Never>(nil)
    let isFetchAuthentication = CurrentValueSubject<Bool, Never>(true)
    let isPublishing = CurrentValueSubject<Bool, Never>(false)
    let isBusy = CurrentValueSubject<Bool, Never>(true)
    let isValid = CurrentValueSubject<Bool, Never>(false)
    let shouldDismiss = CurrentValueSubject<Bool, Never>(true)
    let composeViewModel = ComposeViewModel()
    let characterCount = CurrentValueSubject<Int, Never>(0)

    init() {
        viewDidAppear.receive(on: DispatchQueue.main)
            .removeDuplicates()
            .sink { [weak self] viewDidAppear in
                guard let self = self else { return }
                guard viewDidAppear else { return }
                self.setupCoreData()
            }
            .store(in: &disposeBag)

        Publishers.CombineLatest(
            inputItems.removeDuplicates(),
            viewDidAppear.removeDuplicates()
        )
        .receive(on: DispatchQueue.main)
        .sink { [weak self] inputItems, _ in
            guard let self = self else { return }
            self.parse(inputItems: inputItems)
        }
        .store(in: &disposeBag)

        // bind authentication loading state
        authentication
            .map { result in result == nil }
            .assign(to: \.value, on: isFetchAuthentication)
            .store(in: &disposeBag)

        // bind user locked state
        authentication
            .compactMap { result -> Bool? in
                guard let result = result else { return nil }
                switch result {
                case .success(let authentication):
                    return authentication.user.locked
                case .failure:
                    return nil
                }
            }
            .map { locked -> ComposeToolbarView.VisibilitySelectionType in
                locked ? .private : .public
            }
            .assign(to: \.value, on: selectedStatusVisibility)
            .store(in: &disposeBag)

        // bind author
        authentication
            .receive(on: DispatchQueue.main)
            .sink { [weak self] result in
                guard let self = self else { return }
                guard let result = result else { return }
                switch result {
                case .success(let authentication):
                    self.composeViewModel.avatarImageURL = authentication.user.avatarImageURL()
                    self.composeViewModel.authorName = authentication.user.displayNameWithFallback
                    self.composeViewModel.authorUsername = "@" + authentication.user.username
                case .failure:
                    self.composeViewModel.avatarImageURL = nil
                    self.composeViewModel.authorName = " "
                    self.composeViewModel.authorUsername =  " "
                }
            }
            .store(in: &disposeBag)

        // bind authentication to compose view model
        authentication
            .map { result -> MastodonAuthentication? in
                guard let result = result else { return nil }
                switch result {
                case .success(let authentication):
                    return authentication
                case .failure:
                    return nil
                }
            }
            .assign(to: &composeViewModel.$authentication)

        // bind isBusy
        Publishers.CombineLatest(
            isFetchAuthentication,
            isPublishing
        )
        .receive(on: DispatchQueue.main)
        .map { $0 || $1 }
        .assign(to: \.value, on: isBusy)
        .store(in: &disposeBag)

        // pass initial i18n string
        composeViewModel.statusPlaceholder = L10n.Scene.Compose.contentInputPlaceholder
        composeViewModel.contentWarningPlaceholder = L10n.Scene.Compose.ContentWarning.placeholder
        composeViewModel.toolbarHeight = ComposeToolbarView.toolbarHeight

        // bind compose bar button item UI state
        let isComposeContentEmpty = composeViewModel.$statusContent
            .map { $0.isEmpty }

        isComposeContentEmpty
            .assign(to: \.value, on: shouldDismiss)
            .store(in: &disposeBag)

        let isComposeContentValid = composeViewModel.$characterCount
            .map { characterCount -> Bool in
                return characterCount <= ShareViewModel.composeContentLimit
            }
        let isMediaEmpty = composeViewModel.$attachmentViewModels
            .map { $0.isEmpty }
        let isMediaUploadAllSuccess = composeViewModel.$attachmentViewModels
            .map { viewModels in
                viewModels.allSatisfy { $0.uploadStateMachineSubject.value is StatusAttachmentViewModel.UploadState.Finish }
            }

        let isPublishBarButtonItemEnabledPrecondition1 = Publishers.CombineLatest4(
            isComposeContentEmpty,
            isComposeContentValid,
            isMediaEmpty,
            isMediaUploadAllSuccess
        )
        .map { isComposeContentEmpty, isComposeContentValid, isMediaEmpty, isMediaUploadAllSuccess -> Bool in
            if isMediaEmpty {
                return isComposeContentValid && !isComposeContentEmpty
            } else {
                return isComposeContentValid && isMediaUploadAllSuccess
            }
        }
        .eraseToAnyPublisher()

        let isPublishBarButtonItemEnabledPrecondition2 = Publishers.CombineLatest(
            isComposeContentEmpty,
            isComposeContentValid
        )
        .map { isComposeContentEmpty, isComposeContentValid -> Bool in
            return isComposeContentValid && !isComposeContentEmpty
        }
        .eraseToAnyPublisher()

        Publishers.CombineLatest(
            isPublishBarButtonItemEnabledPrecondition1,
            isPublishBarButtonItemEnabledPrecondition2
        )
        .map { $0 && $1 }
        .assign(to: \.value, on: isValid)
        .store(in: &disposeBag)

        // bind counter
        composeViewModel.$characterCount
            .assign(to: \.value, on: characterCount)
            .store(in: &disposeBag)

        // setup theme
        setupBackgroundColor(theme: ThemeService.shared.currentTheme.value)
        ThemeService.shared.currentTheme
            .receive(on: DispatchQueue.main)
            .sink { [weak self] theme in
                guard let self = self else { return }
                self.setupBackgroundColor(theme: theme)
            }
            .store(in: &disposeBag)
    }

    private func setupBackgroundColor(theme: Theme) {
        composeViewModel.contentWarningBackgroundColor = Color(theme.contentWarningOverlayBackgroundColor)
    }

}

extension ShareViewModel {
    enum ShareError: Error {
        case `internal`(error: Error)
        case userCancelShare
        case missingAuthentication
    }
}

extension ShareViewModel {
    private func setupCoreData() {
        logger.debug("\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public)")
        DispatchQueue.global().async {
            let _coreDataStack = CoreDataStack()
            self.coreDataStack = _coreDataStack
            self.managedObjectContext = _coreDataStack.persistentContainer.viewContext

            _coreDataStack.didFinishLoad
                .receive(on: RunLoop.main)
                .sink { [weak self] didFinishLoad in
                    guard let self = self else { return }
                    guard didFinishLoad else { return }
                    guard let managedObjectContext = self.managedObjectContext else { return }

                    self.logger.debug("\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch authentication…")
                    managedObjectContext.perform {
                        do {
                            let request = MastodonAuthentication.sortedFetchRequest
                            let authentications = try managedObjectContext.fetch(request)
                            let authentication = authentications.sorted(by: { $0.activedAt > $1.activedAt }).first
                            guard let activeAuthentication = authentication else {
                                self.authentication.value = .failure(ShareError.missingAuthentication)
                                return
                            }
                            self.authentication.value = .success(activeAuthentication)
                            self.logger.debug("\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch authentication success \(activeAuthentication.userID)")
                        } catch {
                            self.authentication.value = .failure(ShareError.internal(error: error))
                            self.logger.debug("\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch authentication fail \(error.localizedDescription)")
                            assertionFailure(error.localizedDescription)
                        }
                    }
                }
                .store(in: &self.disposeBag)
        }
    }
}

extension ShareViewModel {
    func parse(inputItems: [NSExtensionItem]) {
        var itemProviders: [NSItemProvider] = []

        for item in inputItems {
            itemProviders.append(contentsOf: item.attachments ?? [])
        }

        let _movieProvider = itemProviders.first(where: { provider in
            return provider.hasRepresentationConforming(toTypeIdentifier: UTType.movie.identifier, fileOptions: [])
        })

        let imageProviders = itemProviders.filter { provider in
            return provider.hasRepresentationConforming(toTypeIdentifier: UTType.image.identifier, fileOptions: [])
        }

        if let movieProvider = _movieProvider {
            composeViewModel.setupAttachmentViewModels([
                StatusAttachmentViewModel(itemProvider: movieProvider)
            ])
        } else {
            let viewModels = imageProviders.map { provider in
                StatusAttachmentViewModel(itemProvider: provider)
            }
            composeViewModel.setupAttachmentViewModels(viewModels)
        }
    }
}

extension ShareViewModel {
    func publish() -> AnyPublisher<Mastodon.Response.Content<Mastodon.Entity.Status>, Error> {
        guard let authentication = composeViewModel.authentication else {
            return Fail(error: APIService.APIError.implicit(.authenticationMissing)).eraseToAnyPublisher()
        }
        let mastodonAuthenticationBox = MastodonAuthenticationBox(
            domain: authentication.domain,
            userID: authentication.userID,
            appAuthorization: Mastodon.API.OAuth.Authorization(accessToken: authentication.appAccessToken),
            userAuthorization: Mastodon.API.OAuth.Authorization(accessToken: authentication.userAccessToken)
        )

        let domain = authentication.domain
        let attachmentViewModels = composeViewModel.attachmentViewModels
        let mediaIDs = attachmentViewModels.compactMap { viewModel in
            viewModel.attachment.value?.id
        }
        let sensitive: Bool = composeViewModel.isContentWarningComposing
        let spoilerText: String? = {
            let text = composeViewModel.contentWarningContent
            guard !text.isEmpty else { return nil }
            return text
        }()
        let visibility = selectedStatusVisibility.value.visibility

        let updateMediaQuerySubscriptions: [AnyPublisher<Mastodon.Response.Content<Mastodon.Entity.Attachment>, Error>] = {
            var subscriptions: [AnyPublisher<Mastodon.Response.Content<Mastodon.Entity.Attachment>, Error>] = []
            for attachmentViewModel in attachmentViewModels {
                guard let attachmentID = attachmentViewModel.attachment.value?.id else { continue }
                let description = attachmentViewModel.descriptionContent.trimmingCharacters(in: .whitespacesAndNewlines)
                guard !description.isEmpty else { continue }
                let query = Mastodon.API.Media.UpdateMediaQuery(
                    file: nil,
                    thumbnail: nil,
                    description: description,
                    focus: nil
                )
                let subscription = APIService.shared.updateMedia(
                    domain: domain,
                    attachmentID: attachmentID,
                    query: query,
                    mastodonAuthenticationBox: mastodonAuthenticationBox
                )
                subscriptions.append(subscription)
            }
            return subscriptions
        }()

        let status = composeViewModel.statusContent

        return Publishers.MergeMany(updateMediaQuerySubscriptions)
            .collect()
            .flatMap { attachments -> AnyPublisher<Mastodon.Response.Content<Mastodon.Entity.Status>, Error> in
                let query = Mastodon.API.Statuses.PublishStatusQuery(
                    status: status,
                    mediaIDs: mediaIDs.isEmpty ? nil : mediaIDs,
                    pollOptions: nil,
                    pollExpiresIn: nil,
                    inReplyToID: nil,
                    sensitive: sensitive,
                    spoilerText: spoilerText,
                    visibility: visibility
                )
                return APIService.shared.publishStatus(
                    domain: domain,
                    query: query,
                    mastodonAuthenticationBox: mastodonAuthenticationBox
                )
            }
            .eraseToAnyPublisher()
    }
}