Merge pull request #3558 from kiwix/Issue#3556

Fixed: Version 3.8.0 shuts down after searching for an entry.

core/src/main/java/org/kiwix/kiwixmobile/core/search/SearchFragment.kt

@@ -61,7 +61,6 @@ import org.kiwix.kiwixmobile.core.search.viewmodel.Action
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ActivityResultReceived
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ClickedSearchInText
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ExitedSearch
-import org.kiwix.kiwixmobile.core.search.viewmodel.Action.Filter
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnItemClick
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnItemLongClick
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnOpenInNewTabClick
@@ -219,7 +218,7 @@ class SearchFragment : BaseFragment() {
           searchView?.setOnQueryTextListener(
             SimpleTextListener {
               if (it.isNotEmpty()) {
-                searchViewModel.actions.trySend(Filter(it)).isSuccess
+                searchViewModel.searchResults(it)
               }
             }
           )

core/src/main/java/org/kiwix/kiwixmobile/core/search/viewmodel/SearchViewModel.kt

@@ -31,6 +31,8 @@ import kotlinx.coroutines.channels.trySendBlocking
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.asFlow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.debounce
+import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.mapLatest
 import kotlinx.coroutines.flow.receiveAsFlow
 import kotlinx.coroutines.launch
@@ -65,6 +67,8 @@ import org.kiwix.kiwixmobile.core.search.viewmodel.effects.StartSpeechInput
 import org.kiwix.libzim.SuggestionSearch
 import javax.inject.Inject
 
+const val DEBOUNCE_DELAY = 500L
+
 @OptIn(ExperimentalCoroutinesApi::class)
 class SearchViewModel @Inject constructor(
   private val recentSearchDao: NewRecentSearchDao,
@@ -88,10 +92,24 @@ class SearchViewModel @Inject constructor(
   val actions = Channel<Action>(Channel.UNLIMITED)
   private val filter = ConflatedBroadcastChannel("")
   private val searchOrigin = ConflatedBroadcastChannel(FromWebView)
+  private val debouncedSearchQuery = MutableStateFlow("")
 
   init {
     viewModelScope.launch { reducer() }
     viewModelScope.launch { actionMapper() }
+    viewModelScope.launch { debouncedSearchQuery() }
+  }
+
+  private suspend fun debouncedSearchQuery() {
+    // Observe and collect the debounced search query
+    debouncedSearchQuery
+      // Applying debouncing to delay the emission of consecutive search queries
+      .debounce(DEBOUNCE_DELAY)
+      // Ensuring that only distinct search queries are processed
+      .distinctUntilChanged()
+      .collect { query ->
+        actions.trySend(Filter(query)).isSuccess
+      }
   }
 
   @Suppress("DEPRECATION")
@@ -201,6 +219,10 @@ class SearchViewModel @Inject constructor(
     }, LATEST)
       .subscribeOn(Schedulers.io())
   }
+
+  fun searchResults(query: String) {
+    debouncedSearchQuery.value = query
+  }
 }
 
 data class SearchResultsWithTerm(val searchTerm: String, val suggestionSearch: SuggestionSearch?)

core/src/test/java/org/kiwix/kiwixmobile/core/search/viewmodel/SearchViewModelTest.kt

@@ -29,10 +29,12 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.consumeAsFlow
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.test.TestCoroutineDispatcher
+import kotlinx.coroutines.test.TestCoroutineScheduler
 import kotlinx.coroutines.test.TestCoroutineScope
 import kotlinx.coroutines.test.TestScope
 import kotlinx.coroutines.test.resetMain
@@ -57,7 +59,6 @@ import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ClickedSearchInText
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ConfirmedDelete
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.CreatedWithArguments
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.ExitedSearch
-import org.kiwix.kiwixmobile.core.search.viewmodel.Action.Filter
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnItemClick
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnItemLongClick
 import org.kiwix.kiwixmobile.core.search.viewmodel.Action.OnOpenInNewTabClick
@@ -109,6 +110,94 @@ internal class SearchViewModelTest {
     viewModel = SearchViewModel(recentSearchDao, zimReaderContainer, searchResultGenerator)
   }
 
+  @Nested
+  inner class DebouncedTest {
+    @Test
+    fun `Search action is debounced`() = runTest {
+      val searchTerm1 = "query1"
+      val searchTerm2 = "query2"
+      val searchTerm3 = "query3"
+      val searchOrigin = FromWebView
+      val suggestionSearch: SuggestionSearch = mockk()
+
+      viewModel.state
+        .test(this)
+        .also {
+          searchResult(searchTerm1, suggestionSearch, testScheduler)
+          delay(100)
+          searchResult(searchTerm2, suggestionSearch, testScheduler)
+          delay(100)
+          searchResult(searchTerm3, suggestionSearch, testScheduler)
+          delay(DEBOUNCE_DELAY)
+          it.assertValue(
+            SearchState(
+              searchTerm3,
+              SearchResultsWithTerm(searchTerm3, suggestionSearch),
+              emptyList(),
+              searchOrigin
+            )
+          )
+        }
+        .finish()
+    }
+
+    @Test
+    fun `Search action is not debounced if time hasn't passed`() = runTest {
+      val searchTerm1 = "query1"
+      val searchTerm2 = "query2"
+      val searchTerm3 = "query3"
+      val searchOrigin = FromWebView
+      val suggestionSearch: SuggestionSearch = mockk()
+
+      viewModel.state
+        .test(this)
+        .also {
+          searchResult(searchTerm1, suggestionSearch, testScheduler)
+          delay(50) // assume user rapidly typing
+          searchResult(searchTerm2, suggestionSearch, testScheduler)
+          delay(50)
+          // test value is not passed to searchResult as time has not passed and user still typing
+          // Match if it is initial `SearchState`
+          it.assertValue(
+            SearchState(
+              "",
+              SearchResultsWithTerm("", null),
+              emptyList(),
+              searchOrigin
+            )
+          )
+          searchResult(searchTerm3, suggestionSearch, testScheduler)
+          delay(DEBOUNCE_DELAY)
+          it.assertValue(
+            SearchState(
+              searchTerm3,
+              SearchResultsWithTerm(searchTerm3, suggestionSearch),
+              emptyList(),
+              searchOrigin
+            )
+          )
+        }
+        .finish()
+    }
+
+    private fun searchResult(
+      searchTerm: String,
+      suggestionSearch: SuggestionSearch,
+      testScheduler: TestCoroutineScheduler
+    ) {
+      coEvery {
+        searchResultGenerator.generateSearchResults(searchTerm, zimFileReader)
+      } returns suggestionSearch
+      viewModel.searchResults(searchTerm)
+      recentsFromDb.trySend(emptyList()).isSuccess
+      viewModel.actions.trySend(ScreenWasStartedFrom(FromWebView)).isSuccess
+      testScheduler.apply {
+        advanceTimeBy(400)
+        runCurrent()
+      }
+    }
+  }
+
   @Nested
   inner class StateTests {
     @Test
@@ -252,7 +341,7 @@ internal class SearchViewModelTest {
     coEvery {
       searchResultGenerator.generateSearchResults(searchTerm, zimFileReader)
     } returns suggestionSearch
-    viewModel.actions.trySend(Filter(searchTerm)).isSuccess
+    viewModel.searchResults(searchTerm)
     recentsFromDb.trySend(databaseResults).isSuccess
     viewModel.actions.trySend(ScreenWasStartedFrom(searchOrigin)).isSuccess
     testScheduler.apply {