//
//  ComposeViewModel.swift
//  Mastodon
//
//  Created by MainasuK Cirno on 2021-3-11.
//

import os.log
import UIKit
import Combine
import CoreData
import CoreDataStack
import GameplayKit
import MastodonSDK

final class ComposeViewModel: NSObject {
    
    static let composeContentLimit: Int = 500
    
    var disposeBag = Set<AnyCancellable>()

    let id = UUID()
    
    // input
    let context: AppContext
    let composeKind: ComposeStatusSection.ComposeKind
    let composeStatusAttribute = ComposeStatusItem.ComposeStatusAttribute()
    let isPollComposing = CurrentValueSubject<Bool, Never>(false)
    let isCustomEmojiComposing = CurrentValueSubject<Bool, Never>(false)
    let isContentWarningComposing = CurrentValueSubject<Bool, Never>(false)
    let selectedStatusVisibility: CurrentValueSubject<ComposeToolbarView.VisibilitySelectionType, Never>
    let activeAuthentication: CurrentValueSubject<MastodonAuthentication?, Never>
    let activeAuthenticationBox: CurrentValueSubject<MastodonAuthenticationBox?, Never>
    let traitCollectionDidChangePublisher = CurrentValueSubject<Void, Never>(Void())      // use CurrentValueSubject to make initial event emit
    let repliedToCellFrame = CurrentValueSubject<CGRect, Never>(.zero)
    let autoCompleteRetryLayoutTimes = CurrentValueSubject<Int, Never>(0)
    let autoCompleteInfo = CurrentValueSubject<ComposeViewController.AutoCompleteInfo?, Never>(nil)
    var isViewAppeared = false
    
    // output
    let composeStatusContentTableViewCell = ComposeStatusContentTableViewCell()
    let composeStatusAttachmentTableViewCell = ComposeStatusAttachmentTableViewCell()
    let composeStatusPollTableViewCell = ComposeStatusPollTableViewCell()

    var dataSource: UITableViewDiffableDataSource<ComposeStatusSection, ComposeStatusItem>!
    var customEmojiPickerDiffableDataSource: UICollectionViewDiffableDataSource<CustomEmojiPickerSection, CustomEmojiPickerItem>!
    private(set) lazy var publishStateMachine: GKStateMachine = {
        // exclude timeline middle fetcher state
        let stateMachine = GKStateMachine(states: [
            PublishState.Initial(viewModel: self),
            PublishState.Publishing(viewModel: self),
            PublishState.Fail(viewModel: self),
            PublishState.Discard(viewModel: self),
            PublishState.Finish(viewModel: self),
        ])
        stateMachine.enter(PublishState.Initial.self)
        return stateMachine
    }()
    private(set) lazy var publishStateMachinePublisher = CurrentValueSubject<PublishState?, Never>(nil)
    private(set) var publishDate = Date()   // update it when enter Publishing state

    // UI & UX
    let title: CurrentValueSubject<String, Never>
    let shouldDismiss = CurrentValueSubject<Bool, Never>(true)
    let isPublishBarButtonItemEnabled = CurrentValueSubject<Bool, Never>(false)
    let isMediaToolbarButtonEnabled = CurrentValueSubject<Bool, Never>(true)
    let isPollToolbarButtonEnabled = CurrentValueSubject<Bool, Never>(true)
    let characterCount = CurrentValueSubject<Int, Never>(0)
    let collectionViewState = CurrentValueSubject<CollectionViewState, Never>(.fold)
    
    // for hashtag: "#<hashtag> "
    // for mention: "@<mention> "
    private(set) var preInsertedContent: String?
    
    // custom emojis
    var customEmojiViewModelSubscription: AnyCancellable?
    let customEmojiViewModel = CurrentValueSubject<EmojiService.CustomEmojiViewModel?, Never>(nil)
    let customEmojiPickerInputViewModel = CustomEmojiPickerInputViewModel()
    let isLoadingCustomEmoji = CurrentValueSubject<Bool, Never>(false)
    
    // attachment
    let attachmentServices = CurrentValueSubject<[MastodonAttachmentService], Never>([])
    
    // polls
    let pollOptionAttributes = CurrentValueSubject<[ComposeStatusPollItem.PollOptionAttribute], Never>([])
    let pollExpiresOptionAttribute = ComposeStatusPollItem.PollExpiresOptionAttribute()
    
    init(
        context: AppContext,
        composeKind: ComposeStatusSection.ComposeKind
    ) {
        self.context = context
        self.composeKind = composeKind
        switch composeKind {
        case .post, .hashtag, .mention:       self.title = CurrentValueSubject(L10n.Scene.Compose.Title.newPost)
        case .reply:                          self.title = CurrentValueSubject(L10n.Scene.Compose.Title.newReply)
        }
        self.selectedStatusVisibility = CurrentValueSubject(context.authenticationService.activeMastodonAuthentication.value?.user.locked == true ? .private : .public)
        self.activeAuthentication = CurrentValueSubject(context.authenticationService.activeMastodonAuthentication.value)
        self.activeAuthenticationBox = CurrentValueSubject(context.authenticationService.activeMastodonAuthenticationBox.value)
        super.init()
        // end init
        
        switch composeKind {
        case .reply(let repliedToStatusObjectID):
            context.managedObjectContext.performAndWait {
                guard let status = context.managedObjectContext.object(with: repliedToStatusObjectID) as? Status else { return }
                let composeAuthor: MastodonUser? = {
                    guard let objectID = self.activeAuthentication.value?.user.objectID else { return nil }
                    guard let author = context.managedObjectContext.object(with: objectID) as? MastodonUser else { return nil }
                    return author
                }()
                
                var mentionAccts: [String] = []
                if composeAuthor?.id != status.author.id {
                    mentionAccts.append("@" + status.author.acct)
                }
                let mentions = (status.mentions ?? Set())
                    .sorted(by: { $0.index.intValue < $1.index.intValue })
                    .filter { $0.id != composeAuthor?.id }
                for mention in mentions {
                    mentionAccts.append("@" + mention.acct)
                }
                for acct in mentionAccts {
                    UITextChecker.learnWord(acct)
                }
                if let spoilerText = status.spoilerText, !spoilerText.isEmpty {
                    self.isContentWarningComposing.value = true
                    self.composeStatusAttribute.contentWarningContent.value = spoilerText
                }
                
                let initialComposeContent = mentionAccts.joined(separator: " ")
                let preInsertedContent: String? = initialComposeContent.isEmpty ? nil : initialComposeContent + " "
                self.preInsertedContent = preInsertedContent
                self.composeStatusAttribute.composeContent.value = preInsertedContent
            }
        case .hashtag(let hashtag):
            let initialComposeContent = "#" + hashtag
            UITextChecker.learnWord(initialComposeContent)
            let preInsertedContent = initialComposeContent + " "
            self.preInsertedContent = preInsertedContent
            self.composeStatusAttribute.composeContent.value = preInsertedContent
        case .mention(let mastodonUserObjectID):
            context.managedObjectContext.performAndWait {
                let mastodonUser = context.managedObjectContext.object(with: mastodonUserObjectID) as! MastodonUser
                let initialComposeContent = "@" + mastodonUser.acct
                UITextChecker.learnWord(initialComposeContent)
                let preInsertedContent = initialComposeContent + " "
                self.preInsertedContent = preInsertedContent
                self.composeStatusAttribute.composeContent.value = preInsertedContent
            }
        case .post:
            self.preInsertedContent = nil
        }

        isCustomEmojiComposing
            .assign(to: \.value, on: customEmojiPickerInputViewModel.isCustomEmojiComposing)
            .store(in: &disposeBag)
        
        isContentWarningComposing
            .assign(to: \.value, on: composeStatusAttribute.isContentWarningComposing)
            .store(in: &disposeBag)
        
        // bind active authentication
        context.authenticationService.activeMastodonAuthentication
            .assign(to: \.value, on: activeAuthentication)
            .store(in: &disposeBag)
        context.authenticationService.activeMastodonAuthenticationBox
            .assign(to: \.value, on: activeAuthenticationBox)
            .store(in: &disposeBag)
        
        // bind avatar and names
        activeAuthentication
            .sink { [weak self] mastodonAuthentication in
                guard let self = self else { return }
                let mastodonUser = mastodonAuthentication?.user
                let username = mastodonUser?.username ?? " "

                self.composeStatusAttribute.avatarURL.value = mastodonUser?.avatarImageURL()
                self.composeStatusAttribute.displayName.value = {
                    guard let displayName = mastodonUser?.displayName, !displayName.isEmpty else {
                        return username
                    }
                    return displayName
                }()
                self.composeStatusAttribute.emojiMeta.value = mastodonUser?.emojiMeta ?? [:]
                self.composeStatusAttribute.username.value = username
            }
            .store(in: &disposeBag)
        
        // bind character count
        Publishers.CombineLatest3(
            composeStatusAttribute.composeContent.eraseToAnyPublisher(),
            composeStatusAttribute.isContentWarningComposing.eraseToAnyPublisher(),
            composeStatusAttribute.contentWarningContent.eraseToAnyPublisher()
        )
        .map { composeContent, isContentWarningComposing, contentWarningContent -> Int in
            let composeContent = composeContent ?? ""
            var count = composeContent.count
            if isContentWarningComposing {
                count += contentWarningContent.count
            }
            return count
        }
        .assign(to: \.value, on: characterCount)
        .store(in: &disposeBag)

        // bind compose bar button item UI state
        let isComposeContentEmpty = composeStatusAttribute.composeContent
            .map { ($0 ?? "").isEmpty }
        let isComposeContentValid = characterCount
            .map { characterCount -> Bool in
                return characterCount <= ComposeViewModel.composeContentLimit
            }
        let isMediaEmpty = attachmentServices
            .map { $0.isEmpty }
        let isMediaUploadAllSuccess = attachmentServices
            .map { services in
                services.allSatisfy { $0.uploadStateMachineSubject.value is MastodonAttachmentService.UploadState.Finish }
            }
        let isPollAttributeAllValid = pollOptionAttributes
            .map { pollAttributes in
                pollAttributes.allSatisfy { attribute -> Bool in
                    !attribute.option.value.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
                }
            }
        
        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.CombineLatest4(
            isComposeContentEmpty,
            isComposeContentValid,
            isPollComposing,
            isPollAttributeAllValid
        )
        .map { isComposeContentEmpty, isComposeContentValid, isPollComposing, isPollAttributeAllValid -> Bool in
            if isPollComposing {
                return isComposeContentValid && !isComposeContentEmpty && isPollAttributeAllValid
            } else {
                return isComposeContentValid && !isComposeContentEmpty
            }
        }
        .eraseToAnyPublisher()
        
        Publishers.CombineLatest(
            isPublishBarButtonItemEnabledPrecondition1,
            isPublishBarButtonItemEnabledPrecondition2
        )
        .map { $0 && $1 }
        .assign(to: \.value, on: isPublishBarButtonItemEnabled)
        .store(in: &disposeBag)
        
        // bind modal dismiss state
        composeStatusAttribute.composeContent
            .receive(on: DispatchQueue.main)
            .map { [weak self] content in
                let content = content ?? ""
                if content.isEmpty {
                    return true
                }
                // if preInsertedContent plus a space is equal to the content, simply dismiss the modal
                if let preInsertedContent = self?.preInsertedContent {
                    return content == preInsertedContent
                }
                return false
            }
            .assign(to: \.value, on: shouldDismiss)
            .store(in: &disposeBag)
        
        // bind custom emojis
        context.authenticationService.activeMastodonAuthenticationBox
            .receive(on: DispatchQueue.main)
            .sink { [weak self] activeMastodonAuthenticationBox in
                guard let self = self else { return }
                guard let activeMastodonAuthenticationBox = activeMastodonAuthenticationBox else { return }
                let domain = activeMastodonAuthenticationBox.domain
                
                // trigger dequeue to preload emojis
                self.customEmojiViewModel.value = self.context.emojiService.dequeueCustomEmojiViewModel(for: domain)
            }
            .store(in: &disposeBag)

        // setup attribute updater
        attachmentServices
            .receive(on: DispatchQueue.main)
            .debounce(for: 0.3, scheduler: DispatchQueue.main)
            .sink { attachmentServices in
                // drive service upload state
                // make image upload in the queue
                for attachmentService in attachmentServices {
                    // skip when prefix N task when task finish OR fail OR uploading
                    guard let currentState = attachmentService.uploadStateMachine.currentState else { break }
                    if currentState is MastodonAttachmentService.UploadState.Fail {
                        continue
                    }
                    if currentState is MastodonAttachmentService.UploadState.Finish {
                        continue
                    }
                    if currentState is MastodonAttachmentService.UploadState.Uploading {
                        break
                    }
                    // trigger uploading one by one
                    if currentState is MastodonAttachmentService.UploadState.Initial {
                        attachmentService.uploadStateMachine.enter(MastodonAttachmentService.UploadState.Uploading.self)
                        break
                    }
                }
            }
            .store(in: &disposeBag)
        
        // bind delegate
        attachmentServices
            .sink { [weak self] attachmentServices in
                guard let self = self else { return }
                attachmentServices.forEach { $0.delegate = self }
            }
            .store(in: &disposeBag)
        
        pollOptionAttributes
            .sink { [weak self] pollAttributes in
                guard let self = self else { return }
                pollAttributes.forEach { $0.delegate = self }
            }
            .store(in: &disposeBag)
        
        // bind compose toolbar UI state
        Publishers.CombineLatest(
            isPollComposing.eraseToAnyPublisher(),
            attachmentServices.eraseToAnyPublisher()
        )
        .receive(on: DispatchQueue.main)
        .sink(receiveValue: { [weak self] isPollComposing, attachmentServices in
            guard let self = self else { return }
            let shouldMediaDisable = isPollComposing || attachmentServices.count >= 4
            let shouldPollDisable = attachmentServices.count > 0
            
            self.isMediaToolbarButtonEnabled.value = !shouldMediaDisable
            self.isPollToolbarButtonEnabled.value = !shouldPollDisable
        })
        .store(in: &disposeBag)
    }
    
    deinit {
        os_log(.info, log: .debug, "%{public}s[%{public}ld], %{public}s", ((#file as NSString).lastPathComponent), #line, #function)
    }
    
}

extension ComposeViewModel {
    enum CollectionViewState {
        case fold       // snap to input
        case expand     // snap to reply
    }
}

extension ComposeViewModel {
    func createNewPollOptionIfPossible() {
        guard pollOptionAttributes.value.count < 4 else { return }
        
        let attribute = ComposeStatusPollItem.PollOptionAttribute()
        pollOptionAttributes.value = pollOptionAttributes.value + [attribute]
    }
    
    func updatePublishDate() {
        publishDate = Date()
    }
}

extension ComposeViewModel {
    
    enum AttachmentPrecondition: Error, LocalizedError {
        case videoAttachWithPhoto
        case moreThanOneVideo
        
        var errorDescription: String? {
            return L10n.Common.Alerts.PublishPostFailure.title
        }
        
        var failureReason: String? {
            switch self {
            case .videoAttachWithPhoto:
                return L10n.Common.Alerts.PublishPostFailure.AttachmentsMessage.videoAttachWithPhoto
            case .moreThanOneVideo:
                return L10n.Common.Alerts.PublishPostFailure.AttachmentsMessage.moreThanOneVideo
            }
        }
    }
    
    // check exclusive limit:
    // - up to 1 video
    // - up to 4 photos
    func checkAttachmentPrecondition() throws {
        let attachmentServices = self.attachmentServices.value
        guard !attachmentServices.isEmpty else { return }
        var photoAttachmentServices: [MastodonAttachmentService] = []
        var videoAttachmentServices: [MastodonAttachmentService] = []
        attachmentServices.forEach { service in
            guard let file = service.file.value else {
                assertionFailure()
                return
            }
            switch file {
            case .jpeg, .png, .gif:
                photoAttachmentServices.append(service)
            case .other:
                videoAttachmentServices.append(service)
            }
        }
        
        if !videoAttachmentServices.isEmpty {
            guard videoAttachmentServices.count == 1 else {
                throw AttachmentPrecondition.moreThanOneVideo
            }
            guard photoAttachmentServices.isEmpty else {
                throw AttachmentPrecondition.videoAttachWithPhoto
            }
        }
    }
    
}

// MARK: - MastodonAttachmentServiceDelegate
extension ComposeViewModel: MastodonAttachmentServiceDelegate {
    func mastodonAttachmentService(_ service: MastodonAttachmentService, uploadStateDidChange state: MastodonAttachmentService.UploadState?) {
        // trigger new output event
        attachmentServices.value = attachmentServices.value
    }
}

// MARK: - ComposePollAttributeDelegate
extension ComposeViewModel: ComposePollAttributeDelegate {
    func composePollAttribute(_ attribute: ComposeStatusPollItem.PollOptionAttribute, pollOptionDidChange: String?) {
        // trigger update
        pollOptionAttributes.value = pollOptionAttributes.value
    }
}