Fix pages filename #151

app/src/main/java/org/koitharu/kotatsu/base/domain/MangaUtils.kt

@@ -15,6 +15,7 @@ import org.koitharu.kotatsu.core.parser.MangaRepository
 import org.koitharu.kotatsu.parsers.model.MangaPage
 import org.koitharu.kotatsu.parsers.util.await
 import org.koitharu.kotatsu.parsers.util.medianOrNull
+import java.io.File
 import java.io.InputStream
 import java.util.zip.ZipFile
 
@@ -59,6 +60,14 @@ object MangaUtils : KoinComponent {
 		}
 	}
 
+	suspend fun getImageMimeType(file: File): String? = runInterruptible(Dispatchers.IO) {
+		val options = BitmapFactory.Options().apply {
+			inJustDecodeBounds = true
+		}
+		BitmapFactory.decodeFile(file.path, options)?.recycle()
+		options.outMimeType
+	}
+
 	private fun getBitmapSize(input: InputStream?): Size {
 		val options = BitmapFactory.Options().apply {
 			inJustDecodeBounds = true

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

@@ -2,19 +2,26 @@ package org.koitharu.kotatsu.reader.ui
 
 import android.content.Context
 import android.net.Uri
+import android.webkit.MimeTypeMap
 import androidx.activity.result.ActivityResultLauncher
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.runInterruptible
 import kotlinx.coroutines.suspendCancellableCoroutine
+import kotlinx.coroutines.withContext
 import okhttp3.HttpUrl.Companion.toHttpUrl
 import okio.IOException
+import org.koitharu.kotatsu.base.domain.MangaUtils
 import org.koitharu.kotatsu.local.data.PagesCache
 import org.koitharu.kotatsu.parsers.model.MangaPage
+import org.koitharu.kotatsu.parsers.util.toFileNameSafe
 import org.koitharu.kotatsu.reader.domain.PageLoader
+import java.io.File
 import kotlin.coroutines.Continuation
-import kotlin.coroutines.coroutineContext
 import kotlin.coroutines.resume
 
+private const val MAX_FILENAME_LENGTH = 10
+private const val EXTENSION_FALLBACK = "png"
+
 class PageSaveHelper(
 	private val cache: PagesCache,
 	context: Context,
@@ -28,22 +35,17 @@ class PageSaveHelper(
 		page: MangaPage,
 		saveLauncher: ActivityResultLauncher<String>,
 	): Uri {
-		var pageFile = cache[page.url]
-		var fileName = pageFile?.name
-		if (fileName == null) {
-			fileName = pageLoader.getPageUrl(page).toHttpUrl().pathSegments.last()
-		}
-		val cc = coroutineContext
-		val destination = suspendCancellableCoroutine<Uri> { cont ->
-			continuation = cont
-			Dispatchers.Main.dispatch(cc) {
-				saveLauncher.launch(fileName)
+		val pageUrl = pageLoader.getPageUrl(page)
+		val pageFile = pageLoader.loadPage(page, force = false)
+		val proposedName = getProposedFileName(pageUrl, pageFile)
+		val destination = withContext(Dispatchers.Main) {
+			suspendCancellableCoroutine<Uri> { cont ->
+				continuation = cont
+				saveLauncher.launch(proposedName)
+			}.also {
+				continuation = null
 			}
 		}
-		continuation = null
-		if (pageFile == null) {
-			pageFile = pageLoader.loadPage(page, force = false)
-		}
 		runInterruptible(Dispatchers.IO) {
 			contentResolver.openOutputStream(destination)?.use { output ->
 				pageFile.inputStream().use { input ->
@@ -57,4 +59,19 @@ class PageSaveHelper(
 	fun onActivityResult(uri: Uri): Boolean = continuation?.apply {
 		resume(uri)
 	} != null
+
+	private suspend fun getProposedFileName(url: String, file: File): String {
+		var name = url.toHttpUrl().pathSegments.last()
+		var extension = name.substringAfterLast('.', "")
+		name = name.substringBeforeLast('.')
+		if (extension.length !in 2..4) {
+			val mimeType = MangaUtils.getImageMimeType(file)
+			extension = if (mimeType != null) {
+				MimeTypeMap.getSingleton().getExtensionFromMimeType(mimeType) ?: EXTENSION_FALLBACK
+			} else {
+				EXTENSION_FALLBACK
+			}
+		}
+		return name.toFileNameSafe().take(MAX_FILENAME_LENGTH) + "." + extension
+	}
 }