package eu.kanade.tachiyomi.ui.manga

import android.content.Context
import androidx.compose.material3.SnackbarDuration
import androidx.compose.material3.SnackbarHostState
import androidx.compose.material3.SnackbarResult
import androidx.compose.runtime.Immutable
import androidx.compose.runtime.getValue
import androidx.compose.ui.util.fastAny
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.flowWithLifecycle
import cafe.adriel.voyager.core.model.StateScreenModel
import cafe.adriel.voyager.core.model.screenModelScope
import eu.kanade.core.preference.asState
import eu.kanade.core.util.addOrRemove
import eu.kanade.core.util.insertSeparators
import eu.kanade.domain.chapter.interactor.GetAvailableScanlators
import eu.kanade.domain.chapter.interactor.SetReadStatus
import eu.kanade.domain.chapter.interactor.SyncChaptersWithSource
import eu.kanade.domain.manga.interactor.GetExcludedScanlators
import eu.kanade.domain.manga.interactor.SetExcludedScanlators
import eu.kanade.domain.manga.interactor.UpdateManga
import eu.kanade.domain.manga.model.chaptersFiltered
import eu.kanade.domain.manga.model.downloadedFilter
import eu.kanade.domain.manga.model.toSManga
import eu.kanade.domain.track.interactor.AddTracks
import eu.kanade.domain.track.interactor.RefreshTracks
import eu.kanade.domain.track.interactor.TrackChapter
import eu.kanade.domain.track.model.AutoTrackState
import eu.kanade.domain.track.service.TrackPreferences
import eu.kanade.presentation.manga.DownloadAction
import eu.kanade.presentation.manga.components.ChapterDownloadAction
import eu.kanade.presentation.util.formattedMessage
import eu.kanade.tachiyomi.data.download.DownloadCache
import eu.kanade.tachiyomi.data.download.DownloadManager
import eu.kanade.tachiyomi.data.download.model.Download
import eu.kanade.tachiyomi.data.track.EnhancedTracker
import eu.kanade.tachiyomi.data.track.TrackerManager
import eu.kanade.tachiyomi.network.HttpException
import eu.kanade.tachiyomi.source.Source
import eu.kanade.tachiyomi.ui.reader.setting.ReaderPreferences
import eu.kanade.tachiyomi.util.chapter.getNextUnread
import eu.kanade.tachiyomi.util.removeCovers
import eu.kanade.tachiyomi.util.system.toast
import kotlinx.collections.immutable.ImmutableList
import kotlinx.collections.immutable.toImmutableList
import kotlinx.coroutines.async
import kotlinx.coroutines.awaitAll
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.collectLatest
import kotlinx.coroutines.flow.combine
import kotlinx.coroutines.flow.distinctUntilChanged
import kotlinx.coroutines.flow.filter
import kotlinx.coroutines.flow.update
import kotlinx.coroutines.isActive
import kotlinx.coroutines.launch
import logcat.LogPriority
import mihon.domain.chapter.interactor.FilterChaptersForDownload
import tachiyomi.core.common.i18n.stringResource
import tachiyomi.core.common.preference.CheckboxState
import tachiyomi.core.common.preference.TriState
import tachiyomi.core.common.preference.mapAsCheckboxState
import tachiyomi.core.common.util.lang.launchIO
import tachiyomi.core.common.util.lang.launchNonCancellable
import tachiyomi.core.common.util.lang.withIOContext
import tachiyomi.core.common.util.lang.withUIContext
import tachiyomi.core.common.util.system.logcat
import tachiyomi.domain.category.interactor.GetCategories
import tachiyomi.domain.category.interactor.SetMangaCategories
import tachiyomi.domain.category.model.Category
import tachiyomi.domain.chapter.interactor.SetMangaDefaultChapterFlags
import tachiyomi.domain.chapter.interactor.UpdateChapter
import tachiyomi.domain.chapter.model.Chapter
import tachiyomi.domain.chapter.model.ChapterUpdate
import tachiyomi.domain.chapter.model.NoChaptersException
import tachiyomi.domain.chapter.service.calculateChapterGap
import tachiyomi.domain.chapter.service.getChapterSort
import tachiyomi.domain.library.service.LibraryPreferences
import tachiyomi.domain.manga.interactor.GetDuplicateLibraryManga
import tachiyomi.domain.manga.interactor.GetMangaWithChapters
import tachiyomi.domain.manga.interactor.SetMangaChapterFlags
import tachiyomi.domain.manga.model.Manga
import tachiyomi.domain.manga.model.MangaWithChapterCount
import tachiyomi.domain.manga.model.applyFilter
import tachiyomi.domain.manga.repository.MangaRepository
import tachiyomi.domain.source.service.SourceManager
import tachiyomi.domain.track.interactor.GetTracks
import tachiyomi.i18n.MR
import tachiyomi.source.local.isLocal
import uy.kohesive.injekt.Injekt
import uy.kohesive.injekt.api.get
import kotlin.math.floor

class MangaScreenModel(
    private val context: Context,
    private val lifecycle: Lifecycle,
    private val mangaId: Long,
    private val isFromSource: Boolean,
    private val libraryPreferences: LibraryPreferences = Injekt.get(),
    private val trackPreferences: TrackPreferences = Injekt.get(),
    readerPreferences: ReaderPreferences = Injekt.get(),
    private val trackerManager: TrackerManager = Injekt.get(),
    private val trackChapter: TrackChapter = Injekt.get(),
    private val downloadManager: DownloadManager = Injekt.get(),
    private val downloadCache: DownloadCache = Injekt.get(),
    private val getMangaAndChapters: GetMangaWithChapters = Injekt.get(),
    private val getDuplicateLibraryManga: GetDuplicateLibraryManga = Injekt.get(),
    private val getAvailableScanlators: GetAvailableScanlators = Injekt.get(),
    private val getExcludedScanlators: GetExcludedScanlators = Injekt.get(),
    private val setExcludedScanlators: SetExcludedScanlators = Injekt.get(),
    private val setMangaChapterFlags: SetMangaChapterFlags = Injekt.get(),
    private val setMangaDefaultChapterFlags: SetMangaDefaultChapterFlags = Injekt.get(),
    private val setReadStatus: SetReadStatus = Injekt.get(),
    private val updateChapter: UpdateChapter = Injekt.get(),
    private val updateManga: UpdateManga = Injekt.get(),
    private val syncChaptersWithSource: SyncChaptersWithSource = Injekt.get(),
    private val getCategories: GetCategories = Injekt.get(),
    private val getTracks: GetTracks = Injekt.get(),
    private val addTracks: AddTracks = Injekt.get(),
    private val setMangaCategories: SetMangaCategories = Injekt.get(),
    private val mangaRepository: MangaRepository = Injekt.get(),
    private val filterChaptersForDownload: FilterChaptersForDownload = Injekt.get(),
    val snackbarHostState: SnackbarHostState = SnackbarHostState(),
) : StateScreenModel<MangaScreenModel.State>(State.Loading) {

    private val successState: State.Success?
        get() = state.value as? State.Success

    val manga: Manga?
        get() = successState?.manga

    val source: Source?
        get() = successState?.source

    private val isFavorited: Boolean
        get() = manga?.favorite ?: false

    private val allChapters: List<ChapterList.Item>?
        get() = successState?.chapters

    private val filteredChapters: List<ChapterList.Item>?
        get() = successState?.processedChapters

    val chapterSwipeStartAction = libraryPreferences.swipeToEndAction().get()
    val chapterSwipeEndAction = libraryPreferences.swipeToStartAction().get()
    var autoTrackState = trackPreferences.autoUpdateTrackOnMarkRead().get()

    private val skipFiltered by readerPreferences.skipFiltered().asState(screenModelScope)

    val isUpdateIntervalEnabled =
        LibraryPreferences.MANGA_OUTSIDE_RELEASE_PERIOD in libraryPreferences.autoUpdateMangaRestrictions().get()

    private val selectedPositions: Array<Int> = arrayOf(-1, -1) // first and last selected index in list
    private val selectedChapterIds: HashSet<Long> = HashSet()

    /**
     * Helper function to update the UI state only if it's currently in success state
     */
    private inline fun updateSuccessState(func: (State.Success) -> State.Success) {
        mutableState.update {
            when (it) {
                State.Loading -> it
                is State.Success -> func(it)
            }
        }
    }

    init {
        screenModelScope.launchIO {
            combine(
                getMangaAndChapters.subscribe(mangaId, applyScanlatorFilter = true).distinctUntilChanged(),
                downloadCache.changes,
                downloadManager.queueState,
            ) { mangaAndChapters, _, _ -> mangaAndChapters }
                .flowWithLifecycle(lifecycle)
                .collectLatest { (manga, chapters) ->
                    updateSuccessState {
                        it.copy(
                            manga = manga,
                            chapters = chapters.toChapterListItems(manga),
                        )
                    }
                }
        }

        screenModelScope.launchIO {
            getExcludedScanlators.subscribe(mangaId)
                .flowWithLifecycle(lifecycle)
                .distinctUntilChanged()
                .collectLatest { excludedScanlators ->
                    updateSuccessState {
                        it.copy(excludedScanlators = excludedScanlators)
                    }
                }
        }

        screenModelScope.launchIO {
            getAvailableScanlators.subscribe(mangaId)
                .flowWithLifecycle(lifecycle)
                .distinctUntilChanged()
                .collectLatest { availableScanlators ->
                    updateSuccessState {
                        it.copy(availableScanlators = availableScanlators)
                    }
                }
        }

        observeDownloads()

        screenModelScope.launchIO {
            val manga = getMangaAndChapters.awaitManga(mangaId)
            val chapters = getMangaAndChapters.awaitChapters(mangaId, applyScanlatorFilter = true)
                .toChapterListItems(manga)

            if (!manga.favorite) {
                setMangaDefaultChapterFlags.await(manga)
            }

            val needRefreshInfo = !manga.initialized
            val needRefreshChapter = chapters.isEmpty()

            // Show what we have earlier
            mutableState.update {
                State.Success(
                    manga = manga,
                    source = Injekt.get<SourceManager>().getOrStub(manga.source),
                    isFromSource = isFromSource,
                    chapters = chapters,
                    availableScanlators = getAvailableScanlators.await(mangaId),
                    excludedScanlators = getExcludedScanlators.await(mangaId),
                    isRefreshingData = needRefreshInfo || needRefreshChapter,
                    dialog = null,
                    hideMissingChapters = libraryPreferences.hideMissingChapters().get(),
                )
            }

            // Start observe tracking since it only needs mangaId
            observeTrackers()

            // Fetch info-chapters when needed
            if (screenModelScope.isActive) {
                val fetchFromSourceTasks = listOf(
                    async { if (needRefreshInfo) fetchMangaFromSource() },
                    async { if (needRefreshChapter) fetchChaptersFromSource() },
                )
                fetchFromSourceTasks.awaitAll()
            }

            // Initial loading finished
            updateSuccessState { it.copy(isRefreshingData = false) }
        }
    }

    fun fetchAllFromSource(manualFetch: Boolean = true) {
        screenModelScope.launch {
            updateSuccessState { it.copy(isRefreshingData = true) }
            val fetchFromSourceTasks = listOf(
                async { fetchMangaFromSource(manualFetch) },
                async { fetchChaptersFromSource(manualFetch) },
            )
            fetchFromSourceTasks.awaitAll()
            updateSuccessState { it.copy(isRefreshingData = false) }
        }
    }

    // Manga info - start

    /**
     * Fetch manga information from source.
     */
    private suspend fun fetchMangaFromSource(manualFetch: Boolean = false) {
        val state = successState ?: return
        try {
            withIOContext {
                val networkManga = state.source.getMangaDetails(state.manga.toSManga())
                updateManga.awaitUpdateFromSource(state.manga, networkManga, manualFetch)
            }
        } catch (e: Throwable) {
            // Ignore early hints "errors" that aren't handled by OkHttp
            if (e is HttpException && e.code == 103) return

            logcat(LogPriority.ERROR, e)
            screenModelScope.launch {
                snackbarHostState.showSnackbar(message = with(context) { e.formattedMessage })
            }
        }
    }

    fun toggleFavorite() {
        toggleFavorite(
            onRemoved = {
                screenModelScope.launch {
                    if (!hasDownloads()) return@launch
                    val result = snackbarHostState.showSnackbar(
                        message = context.stringResource(MR.strings.delete_downloads_for_manga),
                        actionLabel = context.stringResource(MR.strings.action_delete),
                        withDismissAction = true,
                    )
                    if (result == SnackbarResult.ActionPerformed) {
                        deleteDownloads()
                    }
                }
            },
        )
    }

    /**
     * Update favorite status of manga, (removes / adds) manga (to / from) library.
     */
    fun toggleFavorite(
        onRemoved: () -> Unit,
        checkDuplicate: Boolean = true,
    ) {
        val state = successState ?: return
        screenModelScope.launchIO {
            val manga = state.manga

            if (isFavorited) {
                // Remove from library
                if (updateManga.awaitUpdateFavorite(manga.id, false)) {
                    // Remove covers and update last modified in db
                    if (manga.removeCovers() != manga) {
                        updateManga.awaitUpdateCoverLastModified(manga.id)
                    }
                    withUIContext { onRemoved() }
                }
            } else {
                // Add to library
                // First, check if duplicate exists if callback is provided
                if (checkDuplicate) {
                    val duplicates = getDuplicateLibraryManga(manga)

                    if (duplicates.isNotEmpty()) {
                        updateSuccessState { it.copy(dialog = Dialog.DuplicateManga(manga, duplicates)) }
                        return@launchIO
                    }
                }

                // Now check if user previously set categories, when available
                val categories = getCategories()
                val defaultCategoryId = libraryPreferences.defaultCategory().get().toLong()
                val defaultCategory = categories.find { it.id == defaultCategoryId }
                when {
                    // Default category set
                    defaultCategory != null -> {
                        val result = updateManga.awaitUpdateFavorite(manga.id, true)
                        if (!result) return@launchIO
                        moveMangaToCategory(defaultCategory)
                    }

                    // Automatic 'Default' or no categories
                    defaultCategoryId == 0L || categories.isEmpty() -> {
                        val result = updateManga.awaitUpdateFavorite(manga.id, true)
                        if (!result) return@launchIO
                        moveMangaToCategory(null)
                    }

                    // Choose a category
                    else -> showChangeCategoryDialog()
                }

                // Finally match with enhanced tracking when available
                addTracks.bindEnhancedTrackers(manga, state.source)
            }
        }
    }

    fun showChangeCategoryDialog() {
        val manga = successState?.manga ?: return
        screenModelScope.launch {
            val categories = getCategories()
            val selection = getMangaCategoryIds(manga)
            updateSuccessState { successState ->
                successState.copy(
                    dialog = Dialog.ChangeCategory(
                        manga = manga,
                        initialSelection = categories.mapAsCheckboxState { it.id in selection }.toImmutableList(),
                    ),
                )
            }
        }
    }

    fun showSetFetchIntervalDialog() {
        val manga = successState?.manga ?: return
        updateSuccessState {
            it.copy(dialog = Dialog.SetFetchInterval(manga))
        }
    }

    fun setFetchInterval(manga: Manga, interval: Int) {
        screenModelScope.launchIO {
            if (
                updateManga.awaitUpdateFetchInterval(
                    // Custom intervals are negative
                    manga.copy(fetchInterval = -interval),
                )
            ) {
                val updatedManga = mangaRepository.getMangaById(manga.id)
                updateSuccessState { it.copy(manga = updatedManga) }
            }
        }
    }

    /**
     * Returns true if the manga has any downloads.
     */
    private fun hasDownloads(): Boolean {
        val manga = successState?.manga ?: return false
        return downloadManager.getDownloadCount(manga) > 0
    }

    /**
     * Deletes all the downloads for the manga.
     */
    private fun deleteDownloads() {
        val state = successState ?: return
        downloadManager.deleteManga(state.manga, state.source)
    }

    /**
     * Get user categories.
     *
     * @return List of categories, not including the default category
     */
    suspend fun getCategories(): List<Category> {
        return getCategories.await().filterNot { it.isSystemCategory }
    }

    /**
     * Gets the category id's the manga is in, if the manga is not in a category, returns the default id.
     *
     * @param manga the manga to get categories from.
     * @return Array of category ids the manga is in, if none returns default id
     */
    private suspend fun getMangaCategoryIds(manga: Manga): List<Long> {
        return getCategories.await(manga.id)
            .map { it.id }
    }

    fun moveMangaToCategoriesAndAddToLibrary(manga: Manga, categories: List<Long>) {
        moveMangaToCategory(categories)
        if (manga.favorite) return

        screenModelScope.launchIO {
            updateManga.awaitUpdateFavorite(manga.id, true)
        }
    }

    /**
     * Move the given manga to categories.
     *
     * @param categories the selected categories.
     */
    private fun moveMangaToCategories(categories: List<Category>) {
        val categoryIds = categories.map { it.id }
        moveMangaToCategory(categoryIds)
    }

    private fun moveMangaToCategory(categoryIds: List<Long>) {
        screenModelScope.launchIO {
            setMangaCategories.await(mangaId, categoryIds)
        }
    }

    /**
     * Move the given manga to the category.
     *
     * @param category the selected category, or null for default category.
     */
    private fun moveMangaToCategory(category: Category?) {
        moveMangaToCategories(listOfNotNull(category))
    }

    // Manga info - end

    // Chapters list - start

    private fun observeDownloads() {
        screenModelScope.launchIO {
            downloadManager.statusFlow()
                .filter { it.manga.id == successState?.manga?.id }
                .catch { error -> logcat(LogPriority.ERROR, error) }
                .flowWithLifecycle(lifecycle)
                .collect {
                    withUIContext {
                        updateDownloadState(it)
                    }
                }
        }

        screenModelScope.launchIO {
            downloadManager.progressFlow()
                .filter { it.manga.id == successState?.manga?.id }
                .catch { error -> logcat(LogPriority.ERROR, error) }
                .flowWithLifecycle(lifecycle)
                .collect {
                    withUIContext {
                        updateDownloadState(it)
                    }
                }
        }
    }

    private fun updateDownloadState(download: Download) {
        updateSuccessState { successState ->
            val modifiedIndex = successState.chapters.indexOfFirst { it.id == download.chapter.id }
            if (modifiedIndex < 0) return@updateSuccessState successState

            val newChapters = successState.chapters.toMutableList().apply {
                val item = removeAt(modifiedIndex)
                    .copy(downloadState = download.status, downloadProgress = download.progress)
                add(modifiedIndex, item)
            }
            successState.copy(chapters = newChapters)
        }
    }

    private fun List<Chapter>.toChapterListItems(manga: Manga): List<ChapterList.Item> {
        val isLocal = manga.isLocal()
        return map { chapter ->
            val activeDownload = if (isLocal) {
                null
            } else {
                downloadManager.getQueuedDownloadOrNull(chapter.id)
            }
            val downloaded = if (isLocal) {
                true
            } else {
                downloadManager.isChapterDownloaded(
                    chapter.name,
                    chapter.scanlator,
                    chapter.url,
                    manga.title,
                    manga.source,
                )
            }
            val downloadState = when {
                activeDownload != null -> activeDownload.status
                downloaded -> Download.State.DOWNLOADED
                else -> Download.State.NOT_DOWNLOADED
            }

            ChapterList.Item(
                chapter = chapter,
                downloadState = downloadState,
                downloadProgress = activeDownload?.progress ?: 0,
                selected = chapter.id in selectedChapterIds,
            )
        }
    }

    /**
     * Requests an updated list of chapters from the source.
     */
    private suspend fun fetchChaptersFromSource(manualFetch: Boolean = false) {
        val state = successState ?: return
        try {
            withIOContext {
                val chapters = state.source.getChapterList(state.manga.toSManga())

                val newChapters = syncChaptersWithSource.await(
                    chapters,
                    state.manga,
                    state.source,
                    manualFetch,
                )

                if (manualFetch) {
                    downloadNewChapters(newChapters)
                }
            }
        } catch (e: Throwable) {
            val message = if (e is NoChaptersException) {
                context.stringResource(MR.strings.no_chapters_error)
            } else {
                logcat(LogPriority.ERROR, e)
                with(context) { e.formattedMessage }
            }

            screenModelScope.launch {
                snackbarHostState.showSnackbar(message = message)
            }
            val newManga = mangaRepository.getMangaById(mangaId)
            updateSuccessState { it.copy(manga = newManga, isRefreshingData = false) }
        }
    }

    /**
     * @throws IllegalStateException if the swipe action is [LibraryPreferences.ChapterSwipeAction.Disabled]
     */
    fun chapterSwipe(chapterItem: ChapterList.Item, swipeAction: LibraryPreferences.ChapterSwipeAction) {
        screenModelScope.launch {
            executeChapterSwipeAction(chapterItem, swipeAction)
        }
    }

    /**
     * @throws IllegalStateException if the swipe action is [LibraryPreferences.ChapterSwipeAction.Disabled]
     */
    private fun executeChapterSwipeAction(
        chapterItem: ChapterList.Item,
        swipeAction: LibraryPreferences.ChapterSwipeAction,
    ) {
        val chapter = chapterItem.chapter
        when (swipeAction) {
            LibraryPreferences.ChapterSwipeAction.ToggleRead -> {
                markChaptersRead(listOf(chapter), !chapter.read)
            }
            LibraryPreferences.ChapterSwipeAction.ToggleBookmark -> {
                bookmarkChapters(listOf(chapter), !chapter.bookmark)
            }
            LibraryPreferences.ChapterSwipeAction.Download -> {
                val downloadAction: ChapterDownloadAction = when (chapterItem.downloadState) {
                    Download.State.ERROR,
                    Download.State.NOT_DOWNLOADED,
                    -> ChapterDownloadAction.START_NOW
                    Download.State.QUEUE,
                    Download.State.DOWNLOADING,
                    -> ChapterDownloadAction.CANCEL
                    Download.State.DOWNLOADED -> ChapterDownloadAction.DELETE
                }
                runChapterDownloadActions(
                    items = listOf(chapterItem),
                    action = downloadAction,
                )
            }
            LibraryPreferences.ChapterSwipeAction.Disabled -> throw IllegalStateException()
        }
    }

    /**
     * Returns the next unread chapter or null if everything is read.
     */
    fun getNextUnreadChapter(): Chapter? {
        val successState = successState ?: return null
        return successState.chapters.getNextUnread(successState.manga)
    }

    private fun getUnreadChapters(): List<Chapter> {
        val chapterItems = if (skipFiltered) filteredChapters.orEmpty() else allChapters.orEmpty()
        return chapterItems
            .filter { (chapter, dlStatus) -> !chapter.read && dlStatus == Download.State.NOT_DOWNLOADED }
            .map { it.chapter }
    }

    private fun getUnreadChaptersSorted(): List<Chapter> {
        val manga = successState?.manga ?: return emptyList()
        val chaptersSorted = getUnreadChapters().sortedWith(getChapterSort(manga))
        return if (manga.sortDescending()) chaptersSorted.reversed() else chaptersSorted
    }

    private fun startDownload(
        chapters: List<Chapter>,
        startNow: Boolean,
    ) {
        val successState = successState ?: return

        screenModelScope.launchNonCancellable {
            if (startNow) {
                val chapterId = chapters.singleOrNull()?.id ?: return@launchNonCancellable
                downloadManager.startDownloadNow(chapterId)
            } else {
                downloadChapters(chapters)
            }

            if (!isFavorited && !successState.hasPromptedToAddBefore) {
                updateSuccessState { state ->
                    state.copy(hasPromptedToAddBefore = true)
                }
                val result = snackbarHostState.showSnackbar(
                    message = context.stringResource(MR.strings.snack_add_to_library),
                    actionLabel = context.stringResource(MR.strings.action_add),
                    withDismissAction = true,
                )
                if (result == SnackbarResult.ActionPerformed && !isFavorited) {
                    toggleFavorite()
                }
            }
        }
    }

    fun runChapterDownloadActions(
        items: List<ChapterList.Item>,
        action: ChapterDownloadAction,
    ) {
        when (action) {
            ChapterDownloadAction.START -> {
                startDownload(items.map { it.chapter }, false)
                if (items.any { it.downloadState == Download.State.ERROR }) {
                    downloadManager.startDownloads()
                }
            }
            ChapterDownloadAction.START_NOW -> {
                val chapter = items.singleOrNull()?.chapter ?: return
                startDownload(listOf(chapter), true)
            }
            ChapterDownloadAction.CANCEL -> {
                val chapterId = items.singleOrNull()?.id ?: return
                cancelDownload(chapterId)
            }
            ChapterDownloadAction.DELETE -> {
                deleteChapters(items.map { it.chapter })
            }
        }
    }

    fun runDownloadAction(action: DownloadAction) {
        val chaptersToDownload = when (action) {
            DownloadAction.NEXT_1_CHAPTER -> getUnreadChaptersSorted().take(1)
            DownloadAction.NEXT_5_CHAPTERS -> getUnreadChaptersSorted().take(5)
            DownloadAction.NEXT_10_CHAPTERS -> getUnreadChaptersSorted().take(10)
            DownloadAction.NEXT_25_CHAPTERS -> getUnreadChaptersSorted().take(25)
            DownloadAction.UNREAD_CHAPTERS -> getUnreadChapters()
        }
        if (chaptersToDownload.isNotEmpty()) {
            startDownload(chaptersToDownload, false)
        }
    }

    private fun cancelDownload(chapterId: Long) {
        val activeDownload = downloadManager.getQueuedDownloadOrNull(chapterId) ?: return
        downloadManager.cancelQueuedDownloads(listOf(activeDownload))
        updateDownloadState(activeDownload.apply { status = Download.State.NOT_DOWNLOADED })
    }

    fun markPreviousChapterRead(pointer: Chapter) {
        val manga = successState?.manga ?: return
        val chapters = filteredChapters.orEmpty().map { it.chapter }
        val prevChapters = if (manga.sortDescending()) chapters.asReversed() else chapters
        val pointerPos = prevChapters.indexOf(pointer)
        if (pointerPos != -1) markChaptersRead(prevChapters.take(pointerPos), true)
    }

    /**
     * Mark the selected chapter list as read/unread.
     * @param chapters the list of selected chapters.
     * @param read whether to mark chapters as read or unread.
     */
    fun markChaptersRead(chapters: List<Chapter>, read: Boolean) {
        toggleAllSelection(false)
        if (chapters.isEmpty()) return
        screenModelScope.launchIO {
            setReadStatus.await(
                read = read,
                chapters = chapters.toTypedArray(),
            )

            if (!read || successState?.hasLoggedInTrackers == false || autoTrackState == AutoTrackState.NEVER) {
                return@launchIO
            }

            refreshTrackers()

            val tracks = getTracks.await(mangaId)
            val maxChapterNumber = chapters.maxOf { it.chapterNumber }
            val shouldPromptTrackingUpdate = tracks.any { track -> maxChapterNumber > track.lastChapterRead }

            if (!shouldPromptTrackingUpdate) return@launchIO
            if (autoTrackState == AutoTrackState.ALWAYS) {
                trackChapter.await(context, mangaId, maxChapterNumber)
                withUIContext {
                    context.toast(context.stringResource(MR.strings.trackers_updated_summary, maxChapterNumber.toInt()))
                }
                return@launchIO
            }

            val result = snackbarHostState.showSnackbar(
                message = context.stringResource(MR.strings.confirm_tracker_update, maxChapterNumber.toInt()),
                actionLabel = context.stringResource(MR.strings.action_ok),
                duration = SnackbarDuration.Short,
                withDismissAction = true,
            )

            if (result == SnackbarResult.ActionPerformed) {
                trackChapter.await(context, mangaId, maxChapterNumber)
            }
        }
    }

    private suspend fun refreshTrackers(
        refreshTracks: RefreshTracks = Injekt.get(),
    ) {
        refreshTracks.await(mangaId)
            .filter { it.first != null }
            .forEach { (track, e) ->
                logcat(LogPriority.ERROR, e) {
                    "Failed to refresh track data mangaId=$mangaId for service ${track!!.id}"
                }
                withUIContext {
                    context.toast(
                        context.stringResource(
                            MR.strings.track_error,
                            track!!.name,
                            e.message ?: "",
                        ),
                    )
                }
            }
    }

    /**
     * Downloads the given list of chapters with the manager.
     * @param chapters the list of chapters to download.
     */
    private fun downloadChapters(chapters: List<Chapter>) {
        val manga = successState?.manga ?: return
        downloadManager.downloadChapters(manga, chapters)
        toggleAllSelection(false)
    }

    /**
     * Bookmarks the given list of chapters.
     * @param chapters the list of chapters to bookmark.
     */
    fun bookmarkChapters(chapters: List<Chapter>, bookmarked: Boolean) {
        screenModelScope.launchIO {
            chapters
                .filterNot { it.bookmark == bookmarked }
                .map { ChapterUpdate(id = it.id, bookmark = bookmarked) }
                .let { updateChapter.awaitAll(it) }
        }
        toggleAllSelection(false)
    }

    /**
     * Deletes the given list of chapter.
     *
     * @param chapters the list of chapters to delete.
     */
    fun deleteChapters(chapters: List<Chapter>) {
        screenModelScope.launchNonCancellable {
            try {
                successState?.let { state ->
                    downloadManager.deleteChapters(
                        chapters,
                        state.manga,
                        state.source,
                    )
                }
            } catch (e: Throwable) {
                logcat(LogPriority.ERROR, e)
            }
        }
    }

    private fun downloadNewChapters(chapters: List<Chapter>) {
        screenModelScope.launchNonCancellable {
            val manga = successState?.manga ?: return@launchNonCancellable
            val chaptersToDownload = filterChaptersForDownload.await(manga, chapters)

            if (chaptersToDownload.isNotEmpty()) {
                downloadChapters(chaptersToDownload)
            }
        }
    }

    /**
     * Sets the read filter and requests an UI update.
     * @param state whether to display only unread chapters or all chapters.
     */
    fun setUnreadFilter(state: TriState) {
        val manga = successState?.manga ?: return

        val flag = when (state) {
            TriState.DISABLED -> Manga.SHOW_ALL
            TriState.ENABLED_IS -> Manga.CHAPTER_SHOW_UNREAD
            TriState.ENABLED_NOT -> Manga.CHAPTER_SHOW_READ
        }
        screenModelScope.launchNonCancellable {
            setMangaChapterFlags.awaitSetUnreadFilter(manga, flag)
        }
    }

    /**
     * Sets the download filter and requests an UI update.
     * @param state whether to display only downloaded chapters or all chapters.
     */
    fun setDownloadedFilter(state: TriState) {
        val manga = successState?.manga ?: return

        val flag = when (state) {
            TriState.DISABLED -> Manga.SHOW_ALL
            TriState.ENABLED_IS -> Manga.CHAPTER_SHOW_DOWNLOADED
            TriState.ENABLED_NOT -> Manga.CHAPTER_SHOW_NOT_DOWNLOADED
        }

        screenModelScope.launchNonCancellable {
            setMangaChapterFlags.awaitSetDownloadedFilter(manga, flag)
        }
    }

    /**
     * Sets the bookmark filter and requests an UI update.
     * @param state whether to display only bookmarked chapters or all chapters.
     */
    fun setBookmarkedFilter(state: TriState) {
        val manga = successState?.manga ?: return

        val flag = when (state) {
            TriState.DISABLED -> Manga.SHOW_ALL
            TriState.ENABLED_IS -> Manga.CHAPTER_SHOW_BOOKMARKED
            TriState.ENABLED_NOT -> Manga.CHAPTER_SHOW_NOT_BOOKMARKED
        }

        screenModelScope.launchNonCancellable {
            setMangaChapterFlags.awaitSetBookmarkFilter(manga, flag)
        }
    }

    /**
     * Sets the active display mode.
     * @param mode the mode to set.
     */
    fun setDisplayMode(mode: Long) {
        val manga = successState?.manga ?: return

        screenModelScope.launchNonCancellable {
            setMangaChapterFlags.awaitSetDisplayMode(manga, mode)
        }
    }

    /**
     * Sets the sorting method and requests an UI update.
     * @param sort the sorting mode.
     */
    fun setSorting(sort: Long) {
        val manga = successState?.manga ?: return

        screenModelScope.launchNonCancellable {
            setMangaChapterFlags.awaitSetSortingModeOrFlipOrder(manga, sort)
        }
    }

    fun setCurrentSettingsAsDefault(applyToExisting: Boolean) {
        val manga = successState?.manga ?: return
        screenModelScope.launchNonCancellable {
            libraryPreferences.setChapterSettingsDefault(manga)
            if (applyToExisting) {
                setMangaDefaultChapterFlags.awaitAll()
            }
            snackbarHostState.showSnackbar(message = context.stringResource(MR.strings.chapter_settings_updated))
        }
    }

    fun resetToDefaultSettings() {
        val manga = successState?.manga ?: return
        screenModelScope.launchNonCancellable {
            setMangaDefaultChapterFlags.await(manga)
        }
    }

    fun toggleSelection(
        item: ChapterList.Item,
        selected: Boolean,
        userSelected: Boolean = false,
        fromLongPress: Boolean = false,
    ) {
        updateSuccessState { successState ->
            val newChapters = successState.processedChapters.toMutableList().apply {
                val selectedIndex = successState.processedChapters.indexOfFirst { it.id == item.chapter.id }
                if (selectedIndex < 0) return@apply

                val selectedItem = get(selectedIndex)
                if ((selectedItem.selected && selected) || (!selectedItem.selected && !selected)) return@apply

                val firstSelection = none { it.selected }
                set(selectedIndex, selectedItem.copy(selected = selected))
                selectedChapterIds.addOrRemove(item.id, selected)

                if (selected && userSelected && fromLongPress) {
                    if (firstSelection) {
                        selectedPositions[0] = selectedIndex
                        selectedPositions[1] = selectedIndex
                    } else {
                        // Try to select the items in-between when possible
                        val range: IntRange
                        if (selectedIndex < selectedPositions[0]) {
                            range = selectedIndex + 1..<selectedPositions[0]
                            selectedPositions[0] = selectedIndex
                        } else if (selectedIndex > selectedPositions[1]) {
                            range = (selectedPositions[1] + 1)..<selectedIndex
                            selectedPositions[1] = selectedIndex
                        } else {
                            // Just select itself
                            range = IntRange.EMPTY
                        }

                        range.forEach {
                            val inbetweenItem = get(it)
                            if (!inbetweenItem.selected) {
                                selectedChapterIds.add(inbetweenItem.id)
                                set(it, inbetweenItem.copy(selected = true))
                            }
                        }
                    }
                } else if (userSelected && !fromLongPress) {
                    if (!selected) {
                        if (selectedIndex == selectedPositions[0]) {
                            selectedPositions[0] = indexOfFirst { it.selected }
                        } else if (selectedIndex == selectedPositions[1]) {
                            selectedPositions[1] = indexOfLast { it.selected }
                        }
                    } else {
                        if (selectedIndex < selectedPositions[0]) {
                            selectedPositions[0] = selectedIndex
                        } else if (selectedIndex > selectedPositions[1]) {
                            selectedPositions[1] = selectedIndex
                        }
                    }
                }
            }
            successState.copy(chapters = newChapters)
        }
    }

    fun toggleAllSelection(selected: Boolean) {
        updateSuccessState { successState ->
            val newChapters = successState.chapters.map {
                selectedChapterIds.addOrRemove(it.id, selected)
                it.copy(selected = selected)
            }
            selectedPositions[0] = -1
            selectedPositions[1] = -1
            successState.copy(chapters = newChapters)
        }
    }

    fun invertSelection() {
        updateSuccessState { successState ->
            val newChapters = successState.chapters.map {
                selectedChapterIds.addOrRemove(it.id, !it.selected)
                it.copy(selected = !it.selected)
            }
            selectedPositions[0] = -1
            selectedPositions[1] = -1
            successState.copy(chapters = newChapters)
        }
    }

    // Chapters list - end

    // Track sheet - start

    private fun observeTrackers() {
        val manga = successState?.manga ?: return

        screenModelScope.launchIO {
            combine(
                getTracks.subscribe(manga.id).catch { logcat(LogPriority.ERROR, it) },
                trackerManager.loggedInTrackersFlow(),
            ) { mangaTracks, loggedInTrackers ->
                // Show only if the service supports this manga's source
                val supportedTrackers = loggedInTrackers.filter { (it as? EnhancedTracker)?.accept(source!!) ?: true }
                val supportedTrackerIds = supportedTrackers.map { it.id }.toHashSet()
                val supportedTrackerTracks = mangaTracks.filter { it.trackerId in supportedTrackerIds }
                supportedTrackerTracks.size to supportedTrackers.isNotEmpty()
            }
                .flowWithLifecycle(lifecycle)
                .distinctUntilChanged()
                .collectLatest { (trackingCount, hasLoggedInTrackers) ->
                    updateSuccessState {
                        it.copy(
                            trackingCount = trackingCount,
                            hasLoggedInTrackers = hasLoggedInTrackers,
                        )
                    }
                }
        }
    }

    // Track sheet - end

    sealed interface Dialog {
        data class ChangeCategory(
            val manga: Manga,
            val initialSelection: ImmutableList<CheckboxState<Category>>,
        ) : Dialog
        data class DeleteChapters(val chapters: List<Chapter>) : Dialog
        data class DuplicateManga(val manga: Manga, val duplicates: List<MangaWithChapterCount>) : Dialog
        data class Migrate(val target: Manga, val current: Manga) : Dialog
        data class SetFetchInterval(val manga: Manga) : Dialog
        data object SettingsSheet : Dialog
        data object TrackSheet : Dialog
        data object FullCover : Dialog
    }

    fun dismissDialog() {
        updateSuccessState { it.copy(dialog = null) }
    }

    fun showDeleteChapterDialog(chapters: List<Chapter>) {
        updateSuccessState { it.copy(dialog = Dialog.DeleteChapters(chapters)) }
    }

    fun showSettingsDialog() {
        updateSuccessState { it.copy(dialog = Dialog.SettingsSheet) }
    }

    fun showTrackDialog() {
        updateSuccessState { it.copy(dialog = Dialog.TrackSheet) }
    }

    fun showCoverDialog() {
        updateSuccessState { it.copy(dialog = Dialog.FullCover) }
    }

    fun showMigrateDialog(duplicate: Manga) {
        val manga = successState?.manga ?: return
        updateSuccessState { it.copy(dialog = Dialog.Migrate(target = manga, current = duplicate)) }
    }

    fun setExcludedScanlators(excludedScanlators: Set<String>) {
        screenModelScope.launchIO {
            setExcludedScanlators.await(mangaId, excludedScanlators)
        }
    }

    sealed interface State {
        @Immutable
        data object Loading : State

        @Immutable
        data class Success(
            val manga: Manga,
            val source: Source,
            val isFromSource: Boolean,
            val chapters: List<ChapterList.Item>,
            val availableScanlators: Set<String>,
            val excludedScanlators: Set<String>,
            val trackingCount: Int = 0,
            val hasLoggedInTrackers: Boolean = false,
            val isRefreshingData: Boolean = false,
            val dialog: Dialog? = null,
            val hasPromptedToAddBefore: Boolean = false,
            val hideMissingChapters: Boolean = false,
        ) : State {
            val processedChapters by lazy {
                chapters.applyFilters(manga).toList()
            }

            val isAnySelected by lazy {
                chapters.fastAny { it.selected }
            }

            val chapterListItems by lazy {
                if (hideMissingChapters) {
                    return@lazy processedChapters
                }

                processedChapters.insertSeparators { before, after ->
                    val (lowerChapter, higherChapter) = if (manga.sortDescending()) {
                        after to before
                    } else {
                        before to after
                    }
                    if (higherChapter == null) return@insertSeparators null

                    if (lowerChapter == null) {
                        floor(higherChapter.chapter.chapterNumber)
                            .toInt()
                            .minus(1)
                            .coerceAtLeast(0)
                    } else {
                        calculateChapterGap(higherChapter.chapter, lowerChapter.chapter)
                    }
                        .takeIf { it > 0 }
                        ?.let { missingCount ->
                            ChapterList.MissingCount(
                                id = "${lowerChapter?.id}-${higherChapter.id}",
                                count = missingCount,
                            )
                        }
                }
            }

            val scanlatorFilterActive: Boolean
                get() = excludedScanlators.intersect(availableScanlators).isNotEmpty()

            val filterActive: Boolean
                get() = scanlatorFilterActive || manga.chaptersFiltered()

            /**
             * Applies the view filters to the list of chapters obtained from the database.
             * @return an observable of the list of chapters filtered and sorted.
             */
            private fun List<ChapterList.Item>.applyFilters(manga: Manga): Sequence<ChapterList.Item> {
                val isLocalManga = manga.isLocal()
                val unreadFilter = manga.unreadFilter
                val downloadedFilter = manga.downloadedFilter
                val bookmarkedFilter = manga.bookmarkedFilter
                return asSequence()
                    .filter { (chapter) -> applyFilter(unreadFilter) { !chapter.read } }
                    .filter { (chapter) -> applyFilter(bookmarkedFilter) { chapter.bookmark } }
                    .filter { applyFilter(downloadedFilter) { it.isDownloaded || isLocalManga } }
                    .sortedWith { (chapter1), (chapter2) -> getChapterSort(manga).invoke(chapter1, chapter2) }
            }
        }
    }
}

@Immutable
sealed class ChapterList {
    @Immutable
    data class MissingCount(
        val id: String,
        val count: Int,
    ) : ChapterList()

    @Immutable
    data class Item(
        val chapter: Chapter,
        val downloadState: Download.State,
        val downloadProgress: Int,
        val selected: Boolean = false,
    ) : ChapterList() {
        val id = chapter.id
        val isDownloaded = downloadState == Download.State.DOWNLOADED
    }
}
