Fix race condition in concurrent append/prepend

app/src/main/kotlin/com/hippo/ehviewer/client/data/FavListUrlBuilder.kt

@@ -25,9 +25,9 @@ import kotlinx.serialization.Serializable
 data class FavListUrlBuilder(
     val favCat: Int = FAV_CAT_ALL,
     val keyword: String? = null,
-    var jumpTo: String? = null,
-    var prev: String? = null,
-    var next: String? = null,
+    private var jumpTo: String? = null,
+    private var prev: String? = null,
+    private var next: String? = null,
 ) {
     val isLocal
         get() = favCat == FAV_CAT_LOCAL
@@ -35,6 +35,7 @@ data class FavListUrlBuilder(
     fun setIndex(index: String?, isNext: Boolean) {
         next = index.takeIf { isNext }
         prev = index.takeUnless { isNext }
+        jumpTo = null
     }
 
     fun build() = ehUrl(EhUrl.FAV_PATH) {

app/src/main/kotlin/com/hippo/ehviewer/client/data/ListUrlBuilder.kt

@@ -24,16 +24,14 @@ import com.hippo.ehviewer.client.ehUrl
 import com.hippo.ehviewer.dao.QuickSearch
 import com.hippo.ehviewer.ui.main.AdvanceTable
 import io.ktor.http.Parameters
-import kotlin.text.toIntOrNull
 import kotlinx.serialization.Serializable
 
 @Serializable
 data class ListUrlBuilder(
     var mode: Int = MODE_NORMAL,
     private var prev: String? = null,
-    var next: String? = null,
-    // Reset to null after initial loading
-    var jumpTo: String? = null,
+    private var next: String? = null,
+    private var jumpTo: String? = null,
     private var range: Int = 0,
     var category: Int = EhUtils.NONE,
     private var mKeyword: String? = null,
@@ -49,11 +47,14 @@ data class ListUrlBuilder(
         next = index.takeIf { isNext }
         prev = index.takeUnless { isNext }
         range = 0
+        jumpTo = null
     }
 
-    fun setJumpTo(to: Int) {
-        jumpTo = to.takeUnless { it == 0 }?.toString()
-    }
+    var page: Int
+        get() = (jumpTo?.toInt() ?: 0) + 1
+        set(value) {
+            jumpTo = (value - 1).takeUnless { it == 0 }?.toString()
+        }
 
     fun setRange(to: Int) {
         range = to
@@ -62,6 +63,11 @@ data class ListUrlBuilder(
         jumpTo = null
     }
 
+    fun setSeek(date: String) {
+        setIndex("2", true)
+        jumpTo = date
+    }
+
     var keyword: String?
         get() = if (MODE_UPLOADER == mode) "uploader:$mKeyword" else mKeyword
         set(keyword) {

app/src/main/kotlin/com/hippo/ehviewer/ui/CommonOperations.kt

@@ -419,7 +419,7 @@ suspend fun showMoveDownloadLabelList(list: Collection<DownloadInfo>): String? {
 }
 
 context(_: DialogState)
-suspend fun awaitSelectDate(): String? {
+suspend fun awaitSelectDate(): String {
     val initial = LocalDate(2007, 3, 21)
     val yesterday = Clock.System.todayIn(TimeZone.UTC).minus(1, DateTimeUnit.DAY)
     val initialMillis = initial.toEpochMillis()
@@ -432,8 +432,7 @@ suspend fun awaitSelectDate(): String? {
             override fun isSelectableDate(utcTimeMillis: Long): Boolean = utcTimeMillis in dateRange
         },
     )
-    val date = dateMillis?.run { toLocalDateTime().date.toString() }
-    return date
+    return dateMillis.toLocalDateTime().date.toString()
 }
 
 context(_: Context, _: DialogState)

app/src/main/kotlin/com/hippo/ehviewer/ui/screen/FavoritesScreen.kt

@@ -313,7 +313,7 @@ fun AnimatedVisibilityScope.FavouritesScreen(navigator: DestinationsNavigator, v
             }
             onClick(EhIcons.Default.GoTo) {
                 val date = awaitSelectDate()
-                refresh(urlBuilder.copy(jumpTo = date))
+                refresh(urlBuilder.copy(jumpTo = date, prev = null, next = "2"))
             }
             onClick(Icons.Default.Refresh) {
                 refresh()

app/src/main/kotlin/com/hippo/ehviewer/ui/screen/FavoritesViewModel.kt

@@ -23,9 +23,13 @@ import com.hippo.ehviewer.client.data.FavListUrlBuilder
 import com.hippo.ehviewer.ui.tools.foldToLoadResult
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import moe.tarsin.coroutines.runSuspendCatching
 
 class FavoritesViewModel(savedStateHandle: SavedStateHandle) : ViewModel() {
+    private val mutex = Mutex()
+
     val urlBuilder by savedStateHandle.saved(MutableStateSerializer()) {
         mutableStateOf(FavListUrlBuilder(favCat = Settings.recentFavCat))
     }
@@ -43,32 +47,26 @@ class FavoritesViewModel(savedStateHandle: SavedStateHandle) : ViewModel() {
                 }
             }
         } else {
-            Pager(PagingConfig(25)) {
+            Pager(PagingConfig(DEFAULT_PAGE_SIZE, prefetchDistance = 20)) {
                 object : PagingSource<String, BaseGalleryInfo>() {
                     override fun getRefreshKey(state: PagingState<String, BaseGalleryInfo>): String? = null
                     override suspend fun load(params: LoadParams<String>) = withIOContext {
-                        val urlBuilder = urlBuilder.value
-                        when (params) {
-                            is LoadParams.Prepend -> urlBuilder.setIndex(params.key, isNext = false)
-                            is LoadParams.Append -> urlBuilder.setIndex(params.key, isNext = true)
-                            is LoadParams.Refresh -> {
-                                val key = params.key
-                                if (key.isNullOrBlank()) {
-                                    if (urlBuilder.jumpTo != null) {
-                                        urlBuilder.next ?: urlBuilder.setIndex("2", true)
-                                    }
-                                } else {
-                                    urlBuilder.setIndex(key, false)
+                        val url = mutex.withLock {
+                            with(urlBuilder.value) {
+                                when (params) {
+                                    is LoadParams.Prepend -> setIndex(params.key, isNext = false)
+                                    is LoadParams.Append -> setIndex(params.key, isNext = true)
+                                    is LoadParams.Refresh -> params.key?.let { setIndex(it, false) }
                                 }
+                                build()
                             }
                         }
                         runSuspendCatching {
-                            EhEngine.getFavorites(urlBuilder.build())
+                            EhEngine.getFavorites(url)
                         }.foldToLoadResult { result ->
                             Settings.favCat = result.catArray.toTypedArray()
                             Settings.favCount = result.countArray.toIntArray()
                             Settings.favCloudCount = result.countArray.sum()
-                            urlBuilder.jumpTo = null
                             LoadResult.Page(result.galleryInfoList, result.prev, result.next)
                         }
                     }
@@ -77,8 +75,10 @@ class FavoritesViewModel(savedStateHandle: SavedStateHandle) : ViewModel() {
         }.flow.map { pagingData ->
             // https://github.com/FooIbar/EhViewer/issues/1190
             // Workaround for duplicate items when sorting by favorited time
-            val gidSet = MutableLongSet(50)
+            val gidSet = MutableLongSet(DEFAULT_PAGE_SIZE)
             pagingData.filter { gidSet.add(it.gid) }
         }
     }.cachedIn(viewModelScope)
 }
+
+private const val DEFAULT_PAGE_SIZE = 50

app/src/main/kotlin/com/hippo/ehviewer/ui/screen/GalleryListScreen.kt

@@ -590,22 +590,21 @@ fun AnimatedVisibilityScope.GalleryListScreen(
         if (urlBuilder.mode != MODE_WHATS_HOT) {
             onClick(EhIcons.Default.GoTo) {
                 if (isTopList) {
-                    val page = urlBuilder.jumpTo?.toIntOrNull() ?: 0
-                    val hint = string(R.string.go_to_hint, page + 1, TOPLIST_PAGES)
+                    val hint = string(R.string.go_to_hint, urlBuilder.page, TOPLIST_PAGES)
                     val text = awaitInputText(title = gotoTitle, hint = hint, isNumber = true) { oriText ->
-                        val goto = ensureNotNull(oriText.trim().toIntOrNull()) { invalidNum } - 1
-                        ensure(goto in 0..<TOPLIST_PAGES) { outOfRange }
-                    }.trim().toInt() - 1
-                    urlBuilder.setJumpTo(text)
+                        val goto = ensureNotNull(oriText.trim().toIntOrNull()) { invalidNum }
+                        ensure(goto in 1..TOPLIST_PAGES) { outOfRange }
+                    }
+                    urlBuilder.page = text.trim().toInt()
                 } else {
                     val date = awaitSelectDate()
-                    urlBuilder.jumpTo = date
+                    urlBuilder.setSeek(date)
                 }
                 data.refresh()
             }
             onClick(Icons.AutoMirrored.Default.LastPage) {
                 if (isTopList) {
-                    urlBuilder.setJumpTo(TOPLIST_PAGES - 1)
+                    urlBuilder.page = TOPLIST_PAGES
                 } else {
                     urlBuilder.setIndex("1", false)
                 }

app/src/main/kotlin/com/hippo/ehviewer/ui/screen/GalleryListViewModel.kt

@@ -17,49 +17,54 @@ import com.hippo.ehviewer.client.data.BaseGalleryInfo
 import com.hippo.ehviewer.client.data.ListUrlBuilder
 import com.hippo.ehviewer.client.data.ListUrlBuilder.Companion.MODE_TOPLIST
 import com.hippo.ehviewer.ui.tools.foldToLoadResult
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import moe.tarsin.coroutines.runSuspendCatching
 
 class GalleryListViewModel(lub: ListUrlBuilder, savedStateHandle: SavedStateHandle) : ViewModel() {
+    private val mutex = Mutex()
+
     val urlBuilder by savedStateHandle.saved(MutableStateSerializer()) {
         mutableStateOf(lub)
     }
 
-    val data = Pager(PagingConfig(25)) {
+    // Use a smaller prefetch distance to avoid prepending an additional page after jumping
+    val data = Pager(PagingConfig(25, prefetchDistance = 20)) {
         object : PagingSource<String, BaseGalleryInfo>() {
             override fun getRefreshKey(state: PagingState<String, BaseGalleryInfo>): String? = null
             override suspend fun load(params: LoadParams<String>) = withIOContext {
                 val urlBuilder = urlBuilder.value
                 if (urlBuilder.mode == MODE_TOPLIST) {
                     // TODO: Since we know total pages, let pager support jump
-                    val key = (params.key ?: urlBuilder.jumpTo)?.toInt() ?: 0
+                    val key: Int
+                    val url = mutex.withLock {
+                        with(urlBuilder) {
+                            params.key?.let { page = it.toInt() }
+                            key = page
+                            build()
+                        }
+                    }
                     val prev = (key - 1).takeIf { it > 0 }
-                    val next = (key + 1).takeIf { it < TOPLIST_PAGES }
+                    val next = (key + 1).takeIf { it <= TOPLIST_PAGES }
                     runSuspendCatching {
-                        urlBuilder.setJumpTo(key)
-                        EhEngine.getGalleryList(urlBuilder.build())
+                        EhEngine.getGalleryList(url)
                     }.foldToLoadResult { result ->
                         LoadResult.Page(result.galleryInfoList, prev?.toString(), next?.toString())
                     }
                 } else {
-                    when (params) {
-                        is LoadParams.Prepend -> urlBuilder.setIndex(params.key, isNext = false)
-                        is LoadParams.Append -> urlBuilder.setIndex(params.key, isNext = true)
-                        is LoadParams.Refresh -> {
-                            val key = params.key
-                            if (key.isNullOrBlank()) {
-                                if (urlBuilder.jumpTo != null) {
-                                    urlBuilder.next ?: urlBuilder.setIndex("2", true)
-                                }
-                            } else {
-                                urlBuilder.setIndex(key, false)
+                    val url = mutex.withLock {
+                        with(urlBuilder) {
+                            when (params) {
+                                is LoadParams.Prepend -> setIndex(params.key, isNext = false)
+                                is LoadParams.Append -> setIndex(params.key, isNext = true)
+                                is LoadParams.Refresh -> params.key?.let { setIndex(it, false) }
                             }
+                            build()
                         }
                     }
                     runSuspendCatching {
-                        val url = urlBuilder.build()
                         EhEngine.getGalleryList(url)
                     }.foldToLoadResult { result ->
-                        urlBuilder.jumpTo = null
                         LoadResult.Page(result.galleryInfoList, result.prev, result.next)
                     }
                 }

app/src/main/kotlin/com/hippo/ehviewer/ui/tools/Dialog.kt

@@ -487,7 +487,7 @@ suspend fun awaitSelectDate(
     initialDisplayMode: DisplayMode = DisplayMode.Picker,
     selectableDates: SelectableDates = DatePickerDefaults.AllDates,
     showModeToggle: Boolean = true,
-): Long? = dialog { cont ->
+): Long = dialog { cont ->
     val state = rememberDatePickerState(
         initialSelectedDateMillis,
         initialDisplayedMonthMillis,
@@ -498,7 +498,7 @@ suspend fun awaitSelectDate(
     DatePickerDialog(
         onDismissRequest = { cont.cancel() },
         confirmButton = {
-            TextButton(onClick = { cont.resume(state.selectedDateMillis) }, shapes = ButtonDefaults.shapes()) {
+            TextButton(onClick = { state.selectedDateMillis?.let { cont.resume(it) } ?: cont.cancel() }, shapes = ButtonDefaults.shapes()) {
                 Text(text = stringResource(id = android.R.string.ok))
             }
         },