Show missing chapter count between two chapters in chapter list (#10096)

* Show missing chapter count between two chapters in chapter list

Closes #8460

* Fix crash

* Lint

* Review changes

* Lint

app/src/main/java/eu/kanade/domain/chapter/model/ChapterFilter.kt

@@ -2,7 +2,7 @@ package eu.kanade.domain.chapter.model
 
 import eu.kanade.domain.manga.model.downloadedFilter
 import eu.kanade.tachiyomi.data.download.DownloadManager
-import eu.kanade.tachiyomi.ui.manga.ChapterItem
+import eu.kanade.tachiyomi.ui.manga.ChapterList
 import tachiyomi.domain.chapter.model.Chapter
 import tachiyomi.domain.chapter.service.getChapterSort
 import tachiyomi.domain.manga.model.Manga
@@ -34,7 +34,7 @@ fun List<Chapter>.applyFilters(manga: Manga, downloadManager: DownloadManager):
  * Applies the view filters to the list of chapters obtained from the database.
  * @return an observable of the list of chapters filtered and sorted.
  */
-fun List<ChapterItem>.applyFilters(manga: Manga): Sequence<ChapterItem> {
+fun List<ChapterList.Item>.applyFilters(manga: Manga): Sequence<ChapterList.Item> {
     val isLocalManga = manga.isLocal()
     val unreadFilter = manga.unreadFilter
     val downloadedFilter = manga.downloadedFilter

app/src/main/java/eu/kanade/presentation/manga/MangaScreen.kt

@@ -5,9 +5,11 @@ import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.core.animateFloatAsState
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.WindowInsetsSides
 import androidx.compose.foundation.layout.asPaddingValues
@@ -26,7 +28,9 @@ import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.PlayArrow
+import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Text
@@ -44,6 +48,7 @@ import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.platform.LocalHapticFeedback
 import androidx.compose.ui.platform.LocalLayoutDirection
+import androidx.compose.ui.res.pluralStringResource
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.util.fastAll
 import androidx.compose.ui.util.fastAny
@@ -61,7 +66,7 @@ import eu.kanade.presentation.util.formatChapterNumber
 import eu.kanade.tachiyomi.R
 import eu.kanade.tachiyomi.data.download.model.Download
 import eu.kanade.tachiyomi.source.getNameForMangaInfo
-import eu.kanade.tachiyomi.ui.manga.ChapterItem
+import eu.kanade.tachiyomi.ui.manga.ChapterList
 import eu.kanade.tachiyomi.ui.manga.MangaScreenModel
 import eu.kanade.tachiyomi.util.lang.toRelativeString
 import eu.kanade.tachiyomi.util.system.copyToClipboard
@@ -75,8 +80,10 @@ import tachiyomi.presentation.core.components.VerticalFastScroller
 import tachiyomi.presentation.core.components.material.ExtendedFloatingActionButton
 import tachiyomi.presentation.core.components.material.PullRefresh
 import tachiyomi.presentation.core.components.material.Scaffold
+import tachiyomi.presentation.core.components.material.padding
 import tachiyomi.presentation.core.util.isScrolledToEnd
 import tachiyomi.presentation.core.util.isScrollingUp
+import tachiyomi.presentation.core.util.secondaryItemAlpha
 import java.text.DateFormat
 import java.util.Date
 
@@ -92,7 +99,7 @@ fun MangaScreen(
     chapterSwipeEndAction: LibraryPreferences.ChapterSwipeAction,
     onBackClicked: () -> Unit,
     onChapterClicked: (Chapter) -> Unit,
-    onDownloadChapter: ((List<ChapterItem>, ChapterDownloadAction) -> Unit)?,
+    onDownloadChapter: ((List<ChapterList.Item>, ChapterDownloadAction) -> Unit)?,
     onAddToLibraryClicked: () -> Unit,
     onWebViewClicked: (() -> Unit)?,
     onWebViewLongClicked: (() -> Unit)?,
@@ -123,10 +130,10 @@ fun MangaScreen(
     onMultiDeleteClicked: (List<Chapter>) -> Unit,
 
     // For chapter swipe
-    onChapterSwipe: (ChapterItem, LibraryPreferences.ChapterSwipeAction) -> Unit,
+    onChapterSwipe: (ChapterList.Item, LibraryPreferences.ChapterSwipeAction) -> Unit,
 
     // Chapter selection
-    onChapterSelected: (ChapterItem, Boolean, Boolean, Boolean) -> Unit,
+    onChapterSelected: (ChapterList.Item, Boolean, Boolean, Boolean) -> Unit,
     onAllChapterSelected: (Boolean) -> Unit,
     onInvertSelection: () -> Unit,
 ) {
@@ -225,7 +232,7 @@ private fun MangaScreenSmallImpl(
     chapterSwipeEndAction: LibraryPreferences.ChapterSwipeAction,
     onBackClicked: () -> Unit,
     onChapterClicked: (Chapter) -> Unit,
-    onDownloadChapter: ((List<ChapterItem>, ChapterDownloadAction) -> Unit)?,
+    onDownloadChapter: ((List<ChapterList.Item>, ChapterDownloadAction) -> Unit)?,
     onAddToLibraryClicked: () -> Unit,
     onWebViewClicked: (() -> Unit)?,
     onWebViewLongClicked: (() -> Unit)?,
@@ -257,16 +264,17 @@ private fun MangaScreenSmallImpl(
     onMultiDeleteClicked: (List<Chapter>) -> Unit,
 
     // For chapter swipe
-    onChapterSwipe: (ChapterItem, LibraryPreferences.ChapterSwipeAction) -> Unit,
+    onChapterSwipe: (ChapterList.Item, LibraryPreferences.ChapterSwipeAction) -> Unit,
 
     // Chapter selection
-    onChapterSelected: (ChapterItem, Boolean, Boolean, Boolean) -> Unit,
+    onChapterSelected: (ChapterList.Item, Boolean, Boolean, Boolean) -> Unit,
     onAllChapterSelected: (Boolean) -> Unit,
     onInvertSelection: () -> Unit,
 ) {
     val chapterListState = rememberLazyListState()
 
     val chapters = remember(state) { state.processedChapters }
+    val listItem = remember(state) { state.chapterListItems }
 
     val isAnySelected by remember {
         derivedStateOf {
@@ -447,7 +455,8 @@ private fun MangaScreenSmallImpl(
 
                     sharedChapterItems(
                         manga = state.manga,
-                        chapters = chapters,
+                        chapters = listItem,
+                        isAnyChapterSelected = chapters.fastAny { it.selected },
                         dateRelativeTime = dateRelativeTime,
                         dateFormat = dateFormat,
                         chapterSwipeStartAction = chapterSwipeStartAction,
@@ -474,7 +483,7 @@ fun MangaScreenLargeImpl(
     chapterSwipeEndAction: LibraryPreferences.ChapterSwipeAction,
     onBackClicked: () -> Unit,
     onChapterClicked: (Chapter) -> Unit,
-    onDownloadChapter: ((List<ChapterItem>, ChapterDownloadAction) -> Unit)?,
+    onDownloadChapter: ((List<ChapterList.Item>, ChapterDownloadAction) -> Unit)?,
     onAddToLibraryClicked: () -> Unit,
     onWebViewClicked: (() -> Unit)?,
     onWebViewLongClicked: (() -> Unit)?,
@@ -506,10 +515,10 @@ fun MangaScreenLargeImpl(
     onMultiDeleteClicked: (List<Chapter>) -> Unit,
 
     // For swipe actions
-    onChapterSwipe: (ChapterItem, LibraryPreferences.ChapterSwipeAction) -> Unit,
+    onChapterSwipe: (ChapterList.Item, LibraryPreferences.ChapterSwipeAction) -> Unit,
 
     // Chapter selection
-    onChapterSelected: (ChapterItem, Boolean, Boolean, Boolean) -> Unit,
+    onChapterSelected: (ChapterList.Item, Boolean, Boolean, Boolean) -> Unit,
     onAllChapterSelected: (Boolean) -> Unit,
     onInvertSelection: () -> Unit,
 ) {
@@ -517,6 +526,7 @@ fun MangaScreenLargeImpl(
     val density = LocalDensity.current
 
     val chapters = remember(state) { state.processedChapters }
+    val listItem = remember(state) { state.chapterListItems }
 
     val isAnySelected by remember {
         derivedStateOf {
@@ -688,7 +698,8 @@ fun MangaScreenLargeImpl(
 
                             sharedChapterItems(
                                 manga = state.manga,
-                                chapters = chapters,
+                                chapters = listItem,
+                                isAnyChapterSelected = chapters.fastAny { it.selected },
                                 dateRelativeTime = dateRelativeTime,
                                 dateFormat = dateFormat,
                                 chapterSwipeStartAction = chapterSwipeStartAction,
@@ -708,12 +719,12 @@ fun MangaScreenLargeImpl(
 
 @Composable
 private fun SharedMangaBottomActionMenu(
-    selected: List<ChapterItem>,
+    selected: List<ChapterList.Item>,
     modifier: Modifier = Modifier,
     onMultiBookmarkClicked: (List<Chapter>, bookmarked: Boolean) -> Unit,
     onMultiMarkAsReadClicked: (List<Chapter>, markAsRead: Boolean) -> Unit,
     onMarkPreviousAsReadClicked: (Chapter) -> Unit,
-    onDownloadChapter: ((List<ChapterItem>, ChapterDownloadAction) -> Unit)?,
+    onDownloadChapter: ((List<ChapterList.Item>, ChapterDownloadAction) -> Unit)?,
     onMultiDeleteClicked: (List<Chapter>) -> Unit,
     fillFraction: Float,
 ) {
@@ -750,92 +761,123 @@ private fun SharedMangaBottomActionMenu(
 
 private fun LazyListScope.sharedChapterItems(
     manga: Manga,
-    chapters: List<ChapterItem>,
+    chapters: List<ChapterList>,
+    isAnyChapterSelected: Boolean,
     dateRelativeTime: Boolean,
     dateFormat: DateFormat,
     chapterSwipeStartAction: LibraryPreferences.ChapterSwipeAction,
     chapterSwipeEndAction: LibraryPreferences.ChapterSwipeAction,
     onChapterClicked: (Chapter) -> Unit,
-    onDownloadChapter: ((List<ChapterItem>, ChapterDownloadAction) -> Unit)?,
-    onChapterSelected: (ChapterItem, Boolean, Boolean, Boolean) -> Unit,
-    onChapterSwipe: (ChapterItem, LibraryPreferences.ChapterSwipeAction) -> Unit,
+    onDownloadChapter: ((List<ChapterList.Item>, ChapterDownloadAction) -> Unit)?,
+    onChapterSelected: (ChapterList.Item, Boolean, Boolean, Boolean) -> Unit,
+    onChapterSwipe: (ChapterList.Item, LibraryPreferences.ChapterSwipeAction) -> Unit,
 ) {
     items(
         items = chapters,
-        key = { "chapter-${it.chapter.id}" },
+        key = { item ->
+            when (item) {
+                is ChapterList.MissingCount -> "missing-count-${item.id}"
+                is ChapterList.Item -> "chapter-${item.id}"
+            }
+        },
         contentType = { MangaScreenItem.CHAPTER },
-    ) { chapterItem ->
+    ) { item ->
         val haptic = LocalHapticFeedback.current
         val context = LocalContext.current
 
-        MangaChapterListItem(
-            title = if (manga.displayMode == Manga.CHAPTER_DISPLAY_NUMBER) {
-                stringResource(
-                    R.string.display_mode_chapter,
-                    formatChapterNumber(chapterItem.chapter.chapterNumber),
-                )
-            } else {
-                chapterItem.chapter.name
-            },
-            date = chapterItem.chapter.dateUpload
-                .takeIf { it > 0L }
-                ?.let {
-                    Date(it).toRelativeString(
-                        context,
-                        dateRelativeTime,
-                        dateFormat,
-                    )
-                },
-            readProgress = chapterItem.chapter.lastPageRead
-                .takeIf { !chapterItem.chapter.read && it > 0L }
-                ?.let {
-                    stringResource(
-                        R.string.chapter_progress,
-                        it + 1,
+        when (item) {
+            is ChapterList.MissingCount -> {
+                Row(
+                    modifier = Modifier.padding(
+                        horizontal = MaterialTheme.padding.medium,
+                        vertical = MaterialTheme.padding.small,
+                    ),
+                    verticalAlignment = Alignment.CenterVertically,
+                    horizontalArrangement = Arrangement.spacedBy(MaterialTheme.padding.medium),
+                ) {
+                    HorizontalDivider(modifier = Modifier.weight(1f))
+                    Text(
+                        text = pluralStringResource(
+                            id = R.plurals.missing_chapters,
+                            count = item.count,
+                            item.count,
+                        ),
+                        modifier = Modifier.secondaryItemAlpha(),
                     )
-                },
-            scanlator = chapterItem.chapter.scanlator.takeIf { !it.isNullOrBlank() },
-            read = chapterItem.chapter.read,
-            bookmark = chapterItem.chapter.bookmark,
-            selected = chapterItem.selected,
-            downloadIndicatorEnabled = chapters.fastAll { !it.selected },
-            downloadStateProvider = { chapterItem.downloadState },
-            downloadProgressProvider = { chapterItem.downloadProgress },
-            chapterSwipeStartAction = chapterSwipeStartAction,
-            chapterSwipeEndAction = chapterSwipeEndAction,
-            onLongClick = {
-                onChapterSelected(chapterItem, !chapterItem.selected, true, true)
-                haptic.performHapticFeedback(HapticFeedbackType.LongPress)
-            },
-            onClick = {
-                onChapterItemClick(
-                    chapterItem = chapterItem,
-                    chapters = chapters,
-                    onToggleSelection = { onChapterSelected(chapterItem, !chapterItem.selected, true, false) },
-                    onChapterClicked = onChapterClicked,
+                    HorizontalDivider(modifier = Modifier.weight(1f))
+                }
+            }
+            is ChapterList.Item -> {
+                MangaChapterListItem(
+                    title = if (manga.displayMode == Manga.CHAPTER_DISPLAY_NUMBER) {
+                        stringResource(
+                            R.string.display_mode_chapter,
+                            formatChapterNumber(item.chapter.chapterNumber),
+                        )
+                    } else {
+                        item.chapter.name
+                    },
+                    date = item.chapter.dateUpload
+                        .takeIf { it > 0L }
+                        ?.let {
+                            Date(it).toRelativeString(
+                                context,
+                                dateRelativeTime,
+                                dateFormat,
+                            )
+                        },
+                    readProgress = item.chapter.lastPageRead
+                        .takeIf { !item.chapter.read && it > 0L }
+                        ?.let {
+                            stringResource(
+                                R.string.chapter_progress,
+                                it + 1,
+                            )
+                        },
+                    scanlator = item.chapter.scanlator.takeIf { !it.isNullOrBlank() },
+                    read = item.chapter.read,
+                    bookmark = item.chapter.bookmark,
+                    selected = item.selected,
+                    downloadIndicatorEnabled = !isAnyChapterSelected,
+                    downloadStateProvider = { item.downloadState },
+                    downloadProgressProvider = { item.downloadProgress },
+                    chapterSwipeStartAction = chapterSwipeStartAction,
+                    chapterSwipeEndAction = chapterSwipeEndAction,
+                    onLongClick = {
+                        onChapterSelected(item, !item.selected, true, true)
+                        haptic.performHapticFeedback(HapticFeedbackType.LongPress)
+                    },
+                    onClick = {
+                        onChapterItemClick(
+                            chapterItem = item,
+                            isAnyChapterSelected = isAnyChapterSelected,
+                            onToggleSelection = { onChapterSelected(item, !item.selected, true, false) },
+                            onChapterClicked = onChapterClicked,
+                        )
+                    },
+                    onDownloadClick = if (onDownloadChapter != null) {
+                        { onDownloadChapter(listOf(item), it) }
+                    } else {
+                        null
+                    },
+                    onChapterSwipe = {
+                        onChapterSwipe(item, it)
+                    },
                 )
-            },
-            onDownloadClick = if (onDownloadChapter != null) {
-                { onDownloadChapter(listOf(chapterItem), it) }
-            } else {
-                null
-            },
-            onChapterSwipe = {
-                onChapterSwipe(chapterItem, it)
-            },
-        )
+            }
+        }
     }
 }
 
 private fun onChapterItemClick(
-    chapterItem: ChapterItem,
-    chapters: List<ChapterItem>,
+    chapterItem: ChapterList.Item,
+    isAnyChapterSelected: Boolean,
     onToggleSelection: (Boolean) -> Unit,
     onChapterClicked: (Chapter) -> Unit,
 ) {
     when {
         chapterItem.selected -> onToggleSelection(false)
-        chapters.fastAny { it.selected } -> onToggleSelection(true)
+        isAnyChapterSelected -> onToggleSelection(true)
         else -> onChapterClicked(chapterItem.chapter)
     }
 }

app/src/main/java/eu/kanade/tachiyomi/ui/manga/MangaScreenModel.kt

@@ -10,6 +10,7 @@ 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.SetReadStatus
 import eu.kanade.domain.chapter.interactor.SyncChaptersWithSource
 import eu.kanade.domain.manga.interactor.UpdateManga
@@ -61,6 +62,7 @@ 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.download.service.DownloadPreferences
 import tachiyomi.domain.library.service.LibraryPreferences
@@ -75,6 +77,7 @@ import tachiyomi.domain.track.interactor.GetTracks
 import tachiyomi.source.local.isLocal
 import uy.kohesive.injekt.Injekt
 import uy.kohesive.injekt.api.get
+import kotlin.math.floor
 
 class MangaScreenModel(
     val context: Context,
@@ -117,10 +120,10 @@ class MangaScreenModel(
     private val isFavorited: Boolean
         get() = manga?.favorite ?: false
 
-    private val allChapters: List<ChapterItem>?
+    private val allChapters: List<ChapterList.Item>?
         get() = successState?.chapters
 
-    private val filteredChapters: List<ChapterItem>?
+    private val filteredChapters: List<ChapterList.Item>?
         get() = successState?.processedChapters
 
     val chapterSwipeStartAction = libraryPreferences.swipeToEndAction().get()
@@ -158,7 +161,7 @@ class MangaScreenModel(
                     updateSuccessState {
                         it.copy(
                             manga = manga,
-                            chapters = chapters.toChapterItems(manga),
+                            chapters = chapters.toChapterListItems(manga),
                         )
                     }
                 }
@@ -169,7 +172,7 @@ class MangaScreenModel(
         screenModelScope.launchIO {
             val manga = getMangaAndChapters.awaitManga(mangaId)
             val chapters = getMangaAndChapters.awaitChapters(mangaId)
-                .toChapterItems(manga)
+                .toChapterListItems(manga)
 
             if (!manga.favorite) {
                 setMangaDefaultChapterFlags.await(manga)
@@ -455,7 +458,7 @@ class MangaScreenModel(
 
     private fun updateDownloadState(download: Download) {
         updateSuccessState { successState ->
-            val modifiedIndex = successState.chapters.indexOfFirst { it.chapter.id == download.chapter.id }
+            val modifiedIndex = successState.chapters.indexOfFirst { it.id == download.chapter.id }
             if (modifiedIndex < 0) return@updateSuccessState successState
 
             val newChapters = successState.chapters.toMutableList().apply {
@@ -467,7 +470,7 @@ class MangaScreenModel(
         }
     }
 
-    private fun List<Chapter>.toChapterItems(manga: Manga): List<ChapterItem> {
+    private fun List<Chapter>.toChapterListItems(manga: Manga): List<ChapterList.Item> {
         val isLocal = manga.isLocal()
         return map { chapter ->
             val activeDownload = if (isLocal) {
@@ -486,7 +489,7 @@ class MangaScreenModel(
                 else -> Download.State.NOT_DOWNLOADED
             }
 
-            ChapterItem(
+            ChapterList.Item(
                 chapter = chapter,
                 downloadState = downloadState,
                 downloadProgress = activeDownload?.progress ?: 0,
@@ -534,7 +537,7 @@ class MangaScreenModel(
     /**
      * @throws IllegalStateException if the swipe action is [LibraryPreferences.ChapterSwipeAction.Disabled]
      */
-    fun chapterSwipe(chapterItem: ChapterItem, swipeAction: LibraryPreferences.ChapterSwipeAction) {
+    fun chapterSwipe(chapterItem: ChapterList.Item, swipeAction: LibraryPreferences.ChapterSwipeAction) {
         screenModelScope.launch {
             executeChapterSwipeAction(chapterItem, swipeAction)
         }
@@ -544,7 +547,7 @@ class MangaScreenModel(
      * @throws IllegalStateException if the swipe action is [LibraryPreferences.ChapterSwipeAction.Disabled]
      */
     private fun executeChapterSwipeAction(
-        chapterItem: ChapterItem,
+        chapterItem: ChapterList.Item,
         swipeAction: LibraryPreferences.ChapterSwipeAction,
     ) {
         val chapter = chapterItem.chapter
@@ -626,7 +629,7 @@ class MangaScreenModel(
     }
 
     fun runChapterDownloadActions(
-        items: List<ChapterItem>,
+        items: List<ChapterList.Item>,
         action: ChapterDownloadAction,
     ) {
         when (action) {
@@ -641,7 +644,7 @@ class MangaScreenModel(
                 startDownload(listOf(chapter), true)
             }
             ChapterDownloadAction.CANCEL -> {
-                val chapterId = items.singleOrNull()?.chapter?.id ?: return
+                val chapterId = items.singleOrNull()?.id ?: return
                 cancelDownload(chapterId)
             }
             ChapterDownloadAction.DELETE -> {
@@ -842,14 +845,14 @@ class MangaScreenModel(
     }
 
     fun toggleSelection(
-        item: ChapterItem,
+        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.chapter.id == item.chapter.id }
+                val selectedIndex = successState.processedChapters.indexOfFirst { it.id == item.chapter.id }
                 if (selectedIndex < 0) return@apply
 
                 val selectedItem = get(selectedIndex)
@@ -857,7 +860,7 @@ class MangaScreenModel(
 
                 val firstSelection = none { it.selected }
                 set(selectedIndex, selectedItem.copy(selected = selected))
-                selectedChapterIds.addOrRemove(item.chapter.id, selected)
+                selectedChapterIds.addOrRemove(item.id, selected)
 
                 if (selected && userSelected && fromLongPress) {
                     if (firstSelection) {
@@ -880,7 +883,7 @@ class MangaScreenModel(
                         range.forEach {
                             val inbetweenItem = get(it)
                             if (!inbetweenItem.selected) {
-                                selectedChapterIds.add(inbetweenItem.chapter.id)
+                                selectedChapterIds.add(inbetweenItem.id)
                                 set(it, inbetweenItem.copy(selected = true))
                             }
                         }
@@ -908,7 +911,7 @@ class MangaScreenModel(
     fun toggleAllSelection(selected: Boolean) {
         updateSuccessState { successState ->
             val newChapters = successState.chapters.map {
-                selectedChapterIds.addOrRemove(it.chapter.id, selected)
+                selectedChapterIds.addOrRemove(it.id, selected)
                 it.copy(selected = selected)
             }
             selectedPositions[0] = -1
@@ -920,7 +923,7 @@ class MangaScreenModel(
     fun invertSelection() {
         updateSuccessState { successState ->
             val newChapters = successState.chapters.map {
-                selectedChapterIds.addOrRemove(it.chapter.id, !it.selected)
+                selectedChapterIds.addOrRemove(it.id, !it.selected)
                 it.copy(selected = !it.selected)
             }
             selectedPositions[0] = -1
@@ -994,7 +997,7 @@ class MangaScreenModel(
             val manga: Manga,
             val source: Source,
             val isFromSource: Boolean,
-            val chapters: List<ChapterItem>,
+            val chapters: List<ChapterList.Item>,
             val trackItems: List<TrackItem> = emptyList(),
             val isRefreshingData: Boolean = false,
             val dialog: Dialog? = null,
@@ -1005,6 +1008,33 @@ class MangaScreenModel(
                 chapters.applyFilters(manga).toList()
             }
 
+            val chapterListItems by lazy {
+                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 trackingAvailable: Boolean
                 get() = trackItems.isNotEmpty()
 
@@ -1015,7 +1045,7 @@ class MangaScreenModel(
              * 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<ChapterItem>.applyFilters(manga: Manga): Sequence<ChapterItem> {
+            private fun List<ChapterList.Item>.applyFilters(manga: Manga): Sequence<ChapterList.Item> {
                 val isLocalManga = manga.isLocal()
                 val unreadFilter = manga.unreadFilter
                 val downloadedFilter = manga.downloadedFilter
@@ -1031,11 +1061,21 @@ class MangaScreenModel(
 }
 
 @Immutable
-data class ChapterItem(
-    val chapter: Chapter,
-    val downloadState: Download.State,
-    val downloadProgress: Int,
-    val selected: Boolean = false,
-) {
-    val isDownloaded = downloadState == Download.State.DOWNLOADED
+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
+    }
 }

app/src/main/java/eu/kanade/tachiyomi/util/chapter/ChapterGetNextUnread.kt

@@ -2,7 +2,7 @@ package eu.kanade.tachiyomi.util.chapter
 
 import eu.kanade.domain.chapter.model.applyFilters
 import eu.kanade.tachiyomi.data.download.DownloadManager
-import eu.kanade.tachiyomi.ui.manga.ChapterItem
+import eu.kanade.tachiyomi.ui.manga.ChapterList
 import tachiyomi.domain.chapter.model.Chapter
 import tachiyomi.domain.manga.model.Manga
 
@@ -22,7 +22,7 @@ fun List<Chapter>.getNextUnread(manga: Manga, downloadManager: DownloadManager):
 /**
  * Gets next unread chapter with filters and sorting applied
  */
-fun List<ChapterItem>.getNextUnread(manga: Manga): Chapter? {
+fun List<ChapterList.Item>.getNextUnread(manga: Manga): Chapter? {
     return applyFilters(manga).let { chapters ->
         if (manga.sortDescending()) {
             chapters.findLast { !it.chapter.read }