fix: probe source availability before showing download progress

Instant server failures (404/HTML error page) no longer flash a 0%
progress bar; the check mirrors the downloader's previous-day fallback
and tolerates transient network errors, which still go through the
downloader's retry path.

app/src/main/java/com/example/research/ReSearchApplication.kt

@@ -62,7 +62,8 @@ class ReSearchApplication : Application() {
 
         downloadManager = DownloadManager(
             dictionaryRepository = downloadDictionaryRepository,
-            unknownErrorMessage = getString(R.string.unknown_error)
+            unknownErrorMessage = getString(R.string.unknown_error),
+            sourceUnavailableMessage = getString(R.string.download_file_not_found)
         )
 
         dictionaryImportManager = DictionaryImportManager(

app/src/main/java/com/example/research/feature/download/DownloadManager.kt

@@ -12,6 +12,7 @@ import kotlin.time.Duration.Companion.seconds
 class DownloadManager(
     private val dictionaryRepository: DictionaryRepository,
     private val unknownErrorMessage: String,
+    private val sourceUnavailableMessage: String,
     dispatcher: CoroutineDispatcher = Dispatchers.IO,
     externalScope: CoroutineScope? = null
 ) {
@@ -49,22 +50,32 @@ class DownloadManager(
         downloadJob = downloadScope.launch {
             mutex.withLock {
                 try {
-                    updateDownloadProgressState(DownloadState.Loading, 0f)
+                    val enabledSources = try {
-
+                        dictionaryRepository.getEnabledSources()
-                    val hasEnabledSources = try {
-                        dictionaryRepository.hasEnabledSources()
                     } catch (_: Exception) {
-                        false
+                        emptyList()
                     }
 
-                    if (!hasEnabledSources) {
+                    if (enabledSources.isEmpty()) {
                         dictionaryRepository.performAllCleanup()
                         updateDownloadProgressState(DownloadState.Success, 1f)
                         return@withLock
                     }
+
+                    val downloadableSources =
+                        dictionaryRepository.filterServerAvailableSources(enabledSources)
+                    if (downloadableSources.isEmpty()) {
+                        updateDownloadProgressState(
+                            DownloadState.Error(sourceUnavailableMessage), 0f
+                        )
+                        return@withLock
+                    }
+
+                    updateDownloadProgressState(DownloadState.Loading, 0f)
+
                     var lastReportedProgressBucket = -1
                     val result = ReSearchTrace.asyncSection(ReSearchTrace.DICTIONARY_DOWNLOAD) {
-                        dictionaryRepository.downloadDictionaries { progress ->
+                        dictionaryRepository.downloadSources(downloadableSources) { progress ->
                             val progressBucket = progressBucket(progress, DOWNLOAD_PROGRESS_STEP_PERCENT)
                             if (progressBucket != lastReportedProgressBucket) {
                                 lastReportedProgressBucket = progressBucket
@@ -130,16 +141,36 @@ class DownloadManager(
         downloadJob = downloadScope.launch {
             mutex.withLock {
                 try {
-                    updateDownloadProgressState(DownloadState.Loading, 0f)
-
                     if (sourceUrls.isEmpty()) {
                         updateDownloadProgressState(DownloadState.Success, 1f)
                         return@withLock
                     }
 
+                    val sources = try {
+                        dictionaryRepository.getEnabledSources(sourceUrls)
+                    } catch (_: Exception) {
+                        emptyList()
+                    }
+
+                    if (sources.isEmpty()) {
+                        updateDownloadProgressState(DownloadState.Success, 1f)
+                        return@withLock
+                    }
+
+                    val downloadableSources =
+                        dictionaryRepository.filterServerAvailableSources(sources)
+                    if (downloadableSources.isEmpty()) {
+                        updateDownloadProgressState(
+                            DownloadState.Error(sourceUnavailableMessage), 0f
+                        )
+                        return@withLock
+                    }
+
+                    updateDownloadProgressState(DownloadState.Loading, 0f)
+
                     var lastReportedProgressBucket = -1
                     val result = ReSearchTrace.asyncSection(ReSearchTrace.DICTIONARY_DOWNLOAD) {
-                        dictionaryRepository.downloadSpecificSources(sourceUrls) { progress ->
+                        dictionaryRepository.downloadSources(downloadableSources) { progress ->
                             val progressBucket = progressBucket(progress, DOWNLOAD_PROGRESS_STEP_PERCENT)
                             if (progressBucket != lastReportedProgressBucket) {
                                 lastReportedProgressBucket = progressBucket

app/src/main/java/com/example/research/feature/download/repository/DictionaryChecker.kt

@@ -12,6 +12,12 @@ import kotlinx.coroutines.withContext
 import okhttp3.OkHttpClient
 import okhttp3.Request
 
+enum class SourceAvailability {
+    AVAILABLE,
+    NOT_FOUND,
+    UNKNOWN
+}
+
 class DictionaryChecker(
     private val fileStorageManager: FileStorageManager,
     private val client: OkHttpClient
@@ -85,7 +91,26 @@ class DictionaryChecker(
         }
     }
 
-    private fun isSourceAvailableOnServer(source: DictionarySource, date: String): Boolean {
+    suspend fun checkSourceAvailability(source: DictionarySource): SourceAvailability =
+        withContext(Dispatchers.IO) {
+            val currentDate = DateUtils.getCurrentDateString()
+            when (probeSource(source, currentDate)) {
+                SourceAvailability.AVAILABLE -> SourceAvailability.AVAILABLE
+                SourceAvailability.UNKNOWN -> SourceAvailability.UNKNOWN
+                SourceAvailability.NOT_FOUND -> {
+                    if (DictionarySource.hasDatePlaceholder(source.urlTemplate)) {
+                        probeSource(source, DateUtils.getPreviousDateString())
+                    } else {
+                        SourceAvailability.NOT_FOUND
+                    }
+                }
+            }
+        }
+
+    private fun isSourceAvailableOnServer(source: DictionarySource, date: String): Boolean =
+        probeSource(source, date) == SourceAvailability.AVAILABLE
+
+    private fun probeSource(source: DictionarySource, date: String): SourceAvailability {
         return try {
             val url = DictionarySource.buildUrl(source.urlTemplate, date)
             val request = Request.Builder()
@@ -94,12 +119,17 @@ class DictionaryChecker(
                 .build()
 
             client.newCall(request).execute().use { response ->
-                response.isSuccessful &&
+                if (response.isSuccessful &&
                     response.header("Content-Type")?.startsWith("text/html") != true
+                ) {
+                    SourceAvailability.AVAILABLE
+                } else {
+                    SourceAvailability.NOT_FOUND
+                }
             }
         } catch (e: Exception) {
             Log.w(TAG, "Failed to check source availability for ${source.urlTemplate}: ${e.message}")
-            false
+            SourceAvailability.UNKNOWN
         }
     }
 

app/src/main/java/com/example/research/feature/download/repository/DictionaryRepository.kt

@@ -8,6 +8,8 @@ import com.example.research.core.domain.model.DictionarySource
 import com.example.research.data.local.preferences.PreferencesManager
 import com.example.research.common.util.FileStorageManager
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.async
+import kotlinx.coroutines.awaitAll
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.withContext
 import okhttp3.OkHttpClient
@@ -40,74 +42,58 @@ class DictionaryRepository(
         checker.areDictionariesUpToDate(uri, sourcesToCheck, files)
     }
 
-    suspend fun hasEnabledSources(): Boolean = withContext(Dispatchers.IO) {
+    suspend fun getEnabledSources(sourceUrls: List<String>? = null): List<DictionarySource> =
-        preferencesManager.dictionarySources.first().any { it.isEnabled }
+        withContext(Dispatchers.IO) {
-    }
+            val enabledSources = preferencesManager.dictionarySources.first()
-
+                .filter { it.isEnabled }
-    suspend fun downloadDictionaries(
+            if (sourceUrls == null) {
-        onProgress: (Float) -> Unit
+                return@withContext enabledSources
-    ): Result<Unit> = withContext(Dispatchers.IO) {
+            }
-        val folderUri = preferencesManager.dictionaryPath
+            val sourceKeys = sourceUrls.mapTo(mutableSetOf(), DictionarySource::identityKey)
-        val uri = Uri.fromFile(File(folderUri))
+            enabledSources.mapNotNull { source ->
-        val files = fileStorageManager.listFilesInFolder(uri)
+                if (DictionarySource.identityKey(source.urlTemplate) !in sourceKeys) {
-        cleaner.deleteCorruptedArchives(uri, files)
+                    null
-
+                } else {
-        synchronized(filesBeforeDownload) {
+                    source.copy(urlTemplate = DictionarySource.normalizeTemplate(source.urlTemplate))
-            filesBeforeDownload = files.map { it.name }.toMutableSet()
+                }
-        }
-
-        val sources = preferencesManager.dictionarySources.first()
-        val enabledSources = sources.filter { it.isEnabled }
-
-        synchronized(downloadedPrefixes) {
-            downloadedPrefixes = enabledSources.mapNotNull {
-                DictionarySource.extractPrefix(it.urlTemplate)
-            }.toMutableSet()
-        }
-
-        downloader.downloadDictionaries(
-            folderUri = uri,
-            sources = enabledSources,
-            onProgress = onProgress
-        )
-    }
-
-    suspend fun downloadSpecificSources(
-        sourceUrls: List<String>,
-        onProgress: (Float) -> Unit
-    ): Result<Unit> = withContext(Dispatchers.IO) {
-        val folderUri = preferencesManager.dictionaryPath
-        val uri = Uri.fromFile(File(folderUri))
-        val files = fileStorageManager.listFilesInFolder(uri)
-        cleaner.deleteCorruptedArchives(uri, files)
-
-        synchronized(filesBeforeDownload) {
-            filesBeforeDownload = files.map { it.name }.toMutableSet()
-        }
-
-        val allSources = preferencesManager.dictionarySources.first()
-        val sourceKeys = sourceUrls.mapTo(mutableSetOf(), DictionarySource::identityKey)
-        val sourcesToDownload = allSources.mapNotNull { source ->
-            if (!source.isEnabled || DictionarySource.identityKey(source.urlTemplate) !in sourceKeys) {
-                null
-            } else {
-                source.copy(urlTemplate = DictionarySource.normalizeTemplate(source.urlTemplate))
             }
         }
 
-        if (sourcesToDownload.isEmpty()) {
+    suspend fun filterServerAvailableSources(
-            return@withContext Result.success(Unit)
+        sources: List<DictionarySource>
+    ): List<DictionarySource> = withContext(Dispatchers.IO) {
+        if (sources.isEmpty()) {
+            return@withContext emptyList()
+        }
+        sources
+            .map { source -> async { source to checker.checkSourceAvailability(source) } }
+            .awaitAll()
+            .filter { (_, availability) -> availability != SourceAvailability.NOT_FOUND }
+            .map { (source, _) -> source }
+    }
+
+    suspend fun downloadSources(
+        sources: List<DictionarySource>,
+        onProgress: (Float) -> Unit
+    ): Result<Unit> = withContext(Dispatchers.IO) {
+        val folderUri = preferencesManager.dictionaryPath
+        val uri = Uri.fromFile(File(folderUri))
+        val files = fileStorageManager.listFilesInFolder(uri)
+        cleaner.deleteCorruptedArchives(uri, files)
+
+        synchronized(filesBeforeDownload) {
+            filesBeforeDownload = files.map { it.name }.toMutableSet()
         }
 
         synchronized(downloadedPrefixes) {
-            downloadedPrefixes = sourcesToDownload.mapNotNull {
+            downloadedPrefixes = sources.mapNotNull {
                 DictionarySource.extractPrefix(it.urlTemplate)
             }.toMutableSet()
         }
 
         downloader.downloadDictionaries(
             folderUri = uri,
-            sources = sourcesToDownload,
+            sources = sources,
             onProgress = onProgress
         )
     }