Preload pages

app/src/main/java/org/koitharu/kotatsu/reader/domain/PageLoader.kt

@@ -10,25 +10,61 @@ import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import okhttp3.OkHttpClient
 import okhttp3.Request
+import okio.Closeable
 import org.koin.core.component.KoinComponent
+import org.koin.core.component.get
 import org.koitharu.kotatsu.core.model.MangaPage
+import org.koitharu.kotatsu.core.model.MangaSource
 import org.koitharu.kotatsu.core.network.CommonHeaders
 import org.koitharu.kotatsu.core.parser.MangaRepository
+import org.koitharu.kotatsu.core.parser.RemoteMangaRepository
 import org.koitharu.kotatsu.local.data.PagesCache
+import org.koitharu.kotatsu.reader.ui.pager.ReaderPage
 import org.koitharu.kotatsu.utils.ext.await
 import org.koitharu.kotatsu.utils.ext.mangaRepositoryOf
 import java.io.File
+import java.util.*
+import java.util.concurrent.atomic.AtomicInteger
 import java.util.zip.ZipFile
 
-class PageLoader(
-	scope: CoroutineScope,
-	private val okHttp: OkHttpClient,
-	private val cache: PagesCache
-) : CoroutineScope by scope, KoinComponent {
+class PageLoader : KoinComponent, Closeable {
 
-	private var repository: MangaRepository? = null
+	val loaderScope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
+
+	private val okHttp = get<OkHttpClient>()
+	private val cache = get<PagesCache>()
 	private val tasks = LongSparseArray<Deferred<File>>()
 	private val convertLock = Mutex()
+	private var repository: MangaRepository? = null
+	private var prefetchQueue = LinkedList<MangaPage>()
+	private val counter = AtomicInteger(0)
+	private var prefetchQueueLimit = 10 // TODO adaptive
+
+	override fun close() {
+		loaderScope.cancel()
+		tasks.clear()
+	}
+
+	fun isPrefetchApplicable(): Boolean {
+		return repository is RemoteMangaRepository
+	}
+
+	fun prefetch(pages: List<ReaderPage>) {
+		synchronized(prefetchQueue) {
+			for (page in pages.asReversed()) {
+				if (tasks.containsKey(page.id)) {
+					continue
+				}
+				prefetchQueue.offerFirst(page.toMangaPage())
+				if (prefetchQueue.size > prefetchQueueLimit) {
+					prefetchQueue.pollLast()
+				}
+			}
+		}
+		if (counter.get() == 0) {
+			onIdle()
+		}
+	}
 
 	suspend fun loadPage(page: MangaPage, force: Boolean): File {
 		if (!force) {
@@ -42,53 +78,14 @@ class PageLoader(
 		} else if (task?.isCancelled == false) {
 			return task.await()
 		}
-		task = loadAsync(page)
+		task = loadPageAsync(page)
 		tasks[page.id] = task
 		return task.await()
 	}
 
-	private fun loadAsync(page: MangaPage): Deferred<File> {
-		var repo = repository
-		if (repo?.source != page.source) {
-			repo = mangaRepositoryOf(page.source)
-			repository = repo
-		}
-		return async(Dispatchers.IO) {
-			val pageUrl = repo.getPageUrl(page)
-			check(pageUrl.isNotBlank()) { "Cannot obtain full image url" }
-			val uri = Uri.parse(pageUrl)
-			if (uri.scheme == "cbz") {
-				val zip = ZipFile(uri.schemeSpecificPart)
-				val entry = zip.getEntry(uri.fragment)
-				zip.getInputStream(entry).use {
-					cache.put(pageUrl, it)
-				}
-			} else {
-				val request = Request.Builder()
-					.url(pageUrl)
-					.get()
-					.header(CommonHeaders.REFERER, page.referer)
-					.header(CommonHeaders.ACCEPT, "image/webp,image/png;q=0.9,image/jpeg,*/*;q=0.8")
-					.cacheControl(CommonHeaders.CACHE_CONTROL_DISABLED)
-					.build()
-				okHttp.newCall(request).await().use { response ->
-					check(response.isSuccessful) {
-						"Invalid response: ${response.code} ${response.message}"
-					}
-					val body = checkNotNull(response.body) {
-						"Null response"
-					}
-					body.byteStream().use {
-						cache.put(pageUrl, it)
-					}
-				}
-			}
-		}
-	}
-
 	suspend fun convertInPlace(file: File) {
-		convertLock.withLock(Lock) {
-			withContext(Dispatchers.Default) {
+		convertLock.withLock {
+			runInterruptible(Dispatchers.Default) {
 				val image = BitmapFactory.decodeFile(file.absolutePath)
 				try {
 					file.outputStream().use { out ->
@@ -101,5 +98,69 @@ class PageLoader(
 		}
 	}
 
-	private companion object Lock
-}
+	private fun onIdle() {
+		synchronized(prefetchQueue) {
+			val page = prefetchQueue.pollFirst() ?: return
+			tasks[page.id] = loadPageAsync(page)
+		}
+	}
+
+	private fun loadPageAsync(page: MangaPage): Deferred<File> {
+		return loaderScope.async {
+			counter.incrementAndGet()
+			try {
+				loadPageImpl(page)
+			} finally {
+				if (counter.decrementAndGet() == 0) {
+					onIdle()
+				}
+			}
+		}
+	}
+
+	@Synchronized
+	private fun getRepository(source: MangaSource): MangaRepository {
+		val result = repository
+		return if (result != null && result.source == source) {
+			result
+		} else {
+			mangaRepositoryOf(source).also { repository = it }
+		}
+	}
+
+	private suspend fun loadPageImpl(page: MangaPage): File {
+		val pageUrl = getRepository(page.source).getPageUrl(page)
+		check(pageUrl.isNotBlank()) { "Cannot obtain full image url" }
+		val uri = Uri.parse(pageUrl)
+		return if (uri.scheme == "cbz") {
+			runInterruptible(Dispatchers.IO) {
+				val zip = ZipFile(uri.schemeSpecificPart)
+				val entry = zip.getEntry(uri.fragment)
+				zip.getInputStream(entry).use {
+					cache.put(pageUrl, it)
+				}
+			}
+		} else {
+			val request = Request.Builder()
+				.url(pageUrl)
+				.get()
+				.header(CommonHeaders.REFERER, page.referer)
+				.header(CommonHeaders.ACCEPT, "image/webp,image/png;q=0.9,image/jpeg,*/*;q=0.8")
+				.cacheControl(CommonHeaders.CACHE_CONTROL_DISABLED)
+				.build()
+			okHttp.newCall(request).await().use { response ->
+				check(response.isSuccessful) {
+					"Invalid response: ${response.code} ${response.message}"
+				}
+				val body = checkNotNull(response.body) {
+					"Null response"
+				}
+				runInterruptible(Dispatchers.IO) {
+					body.byteStream().use {
+						cache.put(pageUrl, it)
+					}
+				}
+			}
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/reader/ui/ReaderViewModel.kt

@@ -22,6 +22,7 @@ import org.koitharu.kotatsu.core.prefs.AppSettings
 import org.koitharu.kotatsu.core.prefs.ReaderMode
 import org.koitharu.kotatsu.core.prefs.ScreenshotsPolicy
 import org.koitharu.kotatsu.history.domain.HistoryRepository
+import org.koitharu.kotatsu.reader.domain.PageLoader
 import org.koitharu.kotatsu.reader.ui.pager.ReaderPage
 import org.koitharu.kotatsu.reader.ui.pager.ReaderUiState
 import org.koitharu.kotatsu.utils.DownloadManagerHelper
@@ -45,6 +46,8 @@ class ReaderViewModel(
 	private val mangaData = MutableStateFlow(intent.manga)
 	private val chapters = LongSparseArray<MangaChapter>()
 
+	val pageLoader = PageLoader()
+
 	val readerMode = MutableLiveData<ReaderMode>()
 	val onPageSaved = SingleLiveEvent<Uri?>()
 	val uiState = combine(
@@ -126,6 +129,11 @@ class ReaderViewModel(
 		subscribeToSettings()
 	}
 
+	override fun onCleared() {
+		pageLoader.close()
+		super.onCleared()
+	}
+
 	fun switchMode(newMode: ReaderMode) {
 		launchJob {
 			val manga = checkNotNull(mangaData.value)
@@ -206,6 +214,9 @@ class ReaderViewModel(
 		if (position >= pages.size - BOUNDS_PAGE_OFFSET) {
 			loadPrevNextChapter(pages.last().chapterId, 1)
 		}
+		if (pageLoader.isPrefetchApplicable()) {
+			pageLoader.prefetch(pages.trySublist(position + 1, position + PREFETCH_LIMIT))
+		}
 	}
 
 	private fun getReaderMode(isWebtoon: Boolean?) = when {
@@ -262,10 +273,21 @@ class ReaderViewModel(
 			.launchIn(viewModelScope + Dispatchers.IO)
 	}
 
+	private fun <T> List<T>.trySublist(fromIndex: Int, toIndex: Int): List<T> {
+		val fromIndexBounded = fromIndex.coerceAtMost(lastIndex)
+		val toIndexBounded = toIndex.coerceIn(fromIndexBounded, lastIndex)
+		return if (fromIndexBounded == toIndexBounded) {
+			emptyList()
+		} else {
+			subList(fromIndexBounded, toIndexBounded)
+		}
+	}
+
 	private companion object : KoinComponent {
 
 		const val BOUNDS_PAGE_OFFSET = 2
 		const val PAGES_TRIM_THRESHOLD = 120
+		const val PREFETCH_LIMIT = 10
 
 		fun saveState(manga: Manga, state: ReaderState) {
 			processLifecycleScope.launch(Dispatchers.Default + IgnoreErrors) {

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/BasePageHolder.kt

@@ -1,6 +1,7 @@
 package org.koitharu.kotatsu.reader.ui.pager
 
 import android.content.Context
+import androidx.annotation.CallSuper
 import androidx.recyclerview.widget.RecyclerView
 import androidx.viewbinding.ViewBinding
 import org.koitharu.kotatsu.core.exceptions.resolve.ExceptionResolver
@@ -33,5 +34,8 @@ abstract class BasePageHolder<B : ViewBinding>(
 
 	protected abstract fun onBind(data: ReaderPage)
 
-	open fun onRecycled() = Unit
+	@CallSuper
+	open fun onRecycled() {
+		delegate.onRecycle()
+	}
 }

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/BaseReader.kt

@@ -3,21 +3,15 @@ package org.koitharu.kotatsu.reader.ui.pager
 import android.os.Bundle
 import android.view.View
 import androidx.core.graphics.Insets
-import androidx.lifecycle.lifecycleScope
 import androidx.viewbinding.ViewBinding
-import org.koin.android.ext.android.get
 import org.koin.androidx.viewmodel.ext.android.sharedViewModel
 import org.koitharu.kotatsu.base.ui.BaseFragment
-import org.koitharu.kotatsu.reader.domain.PageLoader
 import org.koitharu.kotatsu.reader.ui.ReaderState
 import org.koitharu.kotatsu.reader.ui.ReaderViewModel
 
 abstract class BaseReader<B : ViewBinding> : BaseFragment<B>() {
 
 	protected val viewModel by sharedViewModel<ReaderViewModel>()
-	protected val loader by lazy(LazyThreadSafetyMode.NONE) {
-		PageLoader(lifecycleScope, get(), get())
-	}
 	private var stateToSave: ReaderState? = null
 
 	override fun onViewCreated(view: View, savedInstanceState: Bundle?) {

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/PageHolderDelegate.kt

@@ -3,7 +3,10 @@ package org.koitharu.kotatsu.reader.ui.pager
 import android.net.Uri
 import androidx.core.net.toUri
 import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
-import kotlinx.coroutines.*
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.plus
 import org.koitharu.kotatsu.core.exceptions.resolve.ExceptionResolver
 import org.koitharu.kotatsu.core.exceptions.resolve.ResolvableException
 import org.koitharu.kotatsu.core.model.MangaPage
@@ -20,21 +23,22 @@ class PageHolderDelegate(
 	private val settings: AppSettings,
 	private val callback: Callback,
 	private val exceptionResolver: ExceptionResolver
-) : SubsamplingScaleImageView.DefaultOnImageEventListener(), CoroutineScope by loader {
+) : SubsamplingScaleImageView.DefaultOnImageEventListener() {
 
+	private val scope = loader.loaderScope + Dispatchers.Main.immediate
 	private var state = State.EMPTY
 	private var job: Job? = null
 	private var file: File? = null
 	private var error: Throwable? = null
 
 	fun onBind(page: MangaPage) {
-		job = launchInstead(job) {
+		job = scope.launchInstead(job) {
 			doLoad(page, force = false)
 		}
 	}
 
 	fun retry(page: MangaPage) {
-		job = launchInstead(job) {
+		job = scope.launchInstead(job) {
 			(error as? ResolvableException)?.let {
 				exceptionResolver.resolve(it)
 			}
@@ -65,7 +69,7 @@ class PageHolderDelegate(
 		val file = this.file
 		error = e
 		if (state == State.LOADED && e is IOException && file != null && file.exists()) {
-			job = launchAfter(job) {
+			job = scope.launchAfter(job) {
 				state = State.CONVERTING
 				try {
 					loader.convertInPlace(file)

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/reversed/ReversedReaderFragment.kt

@@ -13,7 +13,10 @@ import org.koitharu.kotatsu.reader.ui.pager.BaseReader
 import org.koitharu.kotatsu.reader.ui.pager.BaseReaderAdapter
 import org.koitharu.kotatsu.reader.ui.pager.ReaderPage
 import org.koitharu.kotatsu.reader.ui.pager.standard.PagerReaderFragment
-import org.koitharu.kotatsu.utils.ext.*
+import org.koitharu.kotatsu.utils.ext.doOnPageChanged
+import org.koitharu.kotatsu.utils.ext.recyclerView
+import org.koitharu.kotatsu.utils.ext.resetTransformations
+import org.koitharu.kotatsu.utils.ext.viewLifecycleScope
 import kotlin.math.absoluteValue
 
 class ReversedReaderFragment : BaseReader<FragmentReaderStandardBinding>() {
@@ -27,7 +30,7 @@ class ReversedReaderFragment : BaseReader<FragmentReaderStandardBinding>() {
 
 	override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 		super.onViewCreated(view, savedInstanceState)
-		pagerAdapter = ReversedPagesAdapter(loader, get(), exceptionResolver)
+		pagerAdapter = ReversedPagesAdapter(viewModel.pageLoader, get(), exceptionResolver)
 		with(binding.pager) {
 			adapter = pagerAdapter
 			offscreenPageLimit = 2

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/standard/PageHolder.kt

@@ -37,7 +37,7 @@ open class PageHolder(
 	}
 
 	override fun onRecycled() {
-		delegate.onRecycle()
+		super.onRecycled()
 		binding.ssiv.recycle()
 	}
 

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/standard/PagerReaderFragment.kt

@@ -29,7 +29,7 @@ class PagerReaderFragment : BaseReader<FragmentReaderStandardBinding>() {
 
 	override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 		super.onViewCreated(view, savedInstanceState)
-		pagesAdapter = PagesAdapter(loader, get(), exceptionResolver)
+		pagesAdapter = PagesAdapter(viewModel.pageLoader, get(), exceptionResolver)
 		with(binding.pager) {
 			adapter = pagesAdapter
 			offscreenPageLimit = 2

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/webtoon/WebtoonHolder.kt

@@ -37,7 +37,7 @@ class WebtoonHolder(
 	}
 
 	override fun onRecycled() {
-		delegate.onRecycle()
+		super.onRecycled()
 		binding.ssiv.recycle()
 	}
 

app/src/main/java/org/koitharu/kotatsu/reader/ui/pager/webtoon/WebtoonReaderFragment.kt

@@ -12,7 +12,10 @@ import org.koitharu.kotatsu.reader.ui.ReaderState
 import org.koitharu.kotatsu.reader.ui.pager.BaseReader
 import org.koitharu.kotatsu.reader.ui.pager.BaseReaderAdapter
 import org.koitharu.kotatsu.reader.ui.pager.ReaderPage
-import org.koitharu.kotatsu.utils.ext.*
+import org.koitharu.kotatsu.utils.ext.doOnCurrentItemChanged
+import org.koitharu.kotatsu.utils.ext.findCenterViewPosition
+import org.koitharu.kotatsu.utils.ext.firstItem
+import org.koitharu.kotatsu.utils.ext.viewLifecycleScope
 
 class WebtoonReaderFragment : BaseReader<FragmentReaderWebtoonBinding>() {
 
@@ -26,7 +29,7 @@ class WebtoonReaderFragment : BaseReader<FragmentReaderWebtoonBinding>() {
 
 	override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 		super.onViewCreated(view, savedInstanceState)
-		webtoonAdapter = WebtoonAdapter(loader, get(), exceptionResolver)
+		webtoonAdapter = WebtoonAdapter(viewModel.pageLoader, get(), exceptionResolver)
 		with(binding.recyclerView) {
 			setHasFixedSize(true)
 			adapter = webtoonAdapter

app/src/main/java/org/koitharu/kotatsu/utils/ext/AndroidExt.kt

@@ -4,6 +4,8 @@ import android.content.Context
 import android.net.ConnectivityManager
 import android.net.Network
 import android.net.NetworkRequest
+import android.os.Bundle
+import android.os.Parcelable
 import androidx.appcompat.app.AlertDialog
 import com.google.android.material.dialog.MaterialAlertDialogBuilder
 import kotlinx.coroutines.suspendCancellableCoroutine
@@ -26,4 +28,10 @@ suspend fun ConnectivityManager.waitForNetwork(): Network {
 
 inline fun buildAlertDialog(context: Context, block: MaterialAlertDialogBuilder.() -> Unit): AlertDialog {
 	return MaterialAlertDialogBuilder(context).apply(block).create()
+}
+
+fun <T : Parcelable> Bundle.requireParcelable(key: String): T {
+	return checkNotNull(getParcelable(key)) {
+		"Value for key $key not found"
+	}
 }