Add the refresh button when the character list is empty.

Add the surface color to the dark app theme.
Fix the null safety bug.

app/src/main/java/cz/fel/barysole/ackeetesttask/db/room/AppDatabase.kt

@@ -9,7 +9,7 @@ import cz.fel.barysole.ackeetesttask.model.PaginationInfo
 
 @Database(
     entities = [CharacterInfo::class, PaginationInfo::class],
-    version = 4,
+    version = 1,
     exportSchema = false
 )
 abstract class AppDatabase : RoomDatabase() {

app/src/main/java/cz/fel/barysole/ackeetesttask/db/room/dao/CharacterDao.kt

@@ -20,7 +20,7 @@ interface CharacterDao {
     fun getAll(): PagingSource<Int, CharacterInfo>
 
     @Query("SELECT * FROM CharacterInfo WHERE id=:id")
-    fun getById(id: Long): CharacterInfo
+    fun getById(id: Long): CharacterInfo?
 
     @Query(
         "SELECT * FROM CharacterInfo WHERE " +

app/src/main/java/cz/fel/barysole/ackeetesttask/repository/characters/CharacterRemoteMediator.kt

@@ -88,7 +88,7 @@ class CharacterRemoteMediator(
         appDatabase.characterDao().deleteNotFavorite()
         for (item in items) {
             val itemInDb = appDatabase.characterDao().getById(item.id)
-            if (itemInDb.isFavorite) {
+            if (itemInDb?.isFavorite == true) {
                 appDatabase.characterDao().insert(item.copy(isFavorite = true))
             } else {
                 appDatabase.characterDao().insert(item)

app/src/main/java/cz/fel/barysole/ackeetesttask/ui/screen/characterlist/CharacterListScreen.kt

 package cz.fel.barysole.ackeetesttask.ui.screen.characterlist
 
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.paging.LoadState
 import androidx.paging.compose.collectAsLazyPagingItems
@@ -19,7 +28,7 @@ fun CharacterListScreen(
         color = MaterialTheme.colorScheme.background
     ) {
         characterListViewModel.pagingDataFlow.collectAsLazyPagingItems().let {
-            if (it.loadState.mediator?.refresh is LoadState.Error) {
+            if (it.loadState.mediator?.refresh is LoadState.Error || it.loadState.mediator?.append is LoadState.Error) {
                 characterListViewModel.showLoadingError(true)
             } else {
                 characterListViewModel.showLoadingError(false)
@@ -32,7 +41,23 @@ fun CharacterListScreen(
                     )
                 }
             }
-            CharacterList(it)
+            // todo: there is no pullToRefresh in MD3 at this moment :c Add it later.
+            if (it.itemCount == 0) {
+                Column(
+                    modifier = Modifier.fillMaxWidth().fillMaxHeight(),
+                    verticalArrangement = Arrangement.Center,
+                    horizontalAlignment = Alignment.CenterHorizontally
+                ) {
+                    Button(
+                        onClick = { characterListViewModel.refreshList() },
+                        colors = ButtonDefaults.buttonColors(containerColor = MaterialTheme.colorScheme.surface, contentColor = MaterialTheme.colorScheme.primary)
+                    ) {
+                        Text("Reload")
+                    }
+                }
+            } else {
+                CharacterList(it)
+            }
         }
     }
 }

app/src/main/java/cz/fel/barysole/ackeetesttask/ui/screen/characterlist/CharacterListViewModel.kt

@@ -14,9 +14,9 @@ import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
-import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.onStart
+import kotlinx.coroutines.launch
 import javax.inject.Inject
 
 @OptIn(ExperimentalCoroutinesApi::class)
@@ -34,7 +34,6 @@ class CharacterListViewModel @Inject constructor(
 
     init {
         pagingDataFlow = getAllCharacters
-            .distinctUntilChanged()
             .onStart { emit(Unit) }
             .flatMapLatest { getCharactersPagingData() }
             .cachedIn(viewModelScope)
@@ -44,6 +43,11 @@ class CharacterListViewModel @Inject constructor(
         _uiState.value = UiState(showError = hasError)
     }
 
+    fun refreshList() {
+        showLoadingError(false)
+        viewModelScope.launch { getAllCharacters.emit(Unit) }
+    }
+
     private fun getCharactersPagingData(): Flow<PagingData<CharacterInfo>> =
         characterRepository.getCharactersFlow()
 

app/src/main/java/cz/fel/barysole/ackeetesttask/ui/theme/Color.kt

@@ -9,5 +9,6 @@ val Pink80 = Color(0xFFEFB8C8)
 val Pink40 = Color(0xFF7D5260)
 
 val White = Color(0xFFFFFFFF)
+val DarkGray = Color(0xFF212224)
 val LightGray = Color(0xFFF4F4F9)
 val Gray = Color(0xFFbCBCBC)
\ No newline at end of file

app/src/main/java/cz/fel/barysole/ackeetesttask/ui/theme/Theme.kt

@@ -19,7 +19,8 @@ import androidx.core.view.WindowCompat
 private val DarkColorScheme = darkColorScheme(
     primary = Purple80,
     secondary = PurpleGrey80,
-    tertiary = Pink80
+    tertiary = Pink80,
+    surface = DarkGray
 )
 
 private val LightColorScheme = lightColorScheme(