src: remove cache and simplify db logic

Signed-off-by: Aditya Wasan <adityawasan55@gmail.com>

app/src/main/java/dev/msfjarvis/lobsters/data/remote/LobstersPagingSource.kt

@@ -14,9 +14,17 @@ class LobstersPagingSource @Inject constructor(
   override suspend fun load(params: LoadParams<Int>): LoadResult<Int, LobstersPost> {
     return try {
       val page = params.key ?: 1
-      val savedPosts = lobstersRepository.getCachedPosts()
       val posts = lobstersApi.getHottestPosts(page).map { post ->
-        post.copy(is_saved = savedPosts.contains(post.short_id))
+        // We can replace these two lines below with a getOrInsertPost repository method.
+        val dbPost = lobstersRepository.getPost(post.short_id)
+        return@map if (dbPost == null) {
+          // If db does not contain the post, add it and return the original post
+          lobstersRepository.addPostToDB(post)
+          post
+        } else {
+          // Otherwise return the db post
+          dbPost
+        }
       }
 
       LoadResult.Page(

app/src/main/java/dev/msfjarvis/lobsters/data/repo/LobstersRepository.kt

@@ -8,32 +8,33 @@ import javax.inject.Inject
 
 class LobstersRepository @Inject constructor(private val lobstersDatabase: LobstersDatabase) {
 
-  private var savedPostCache: MutableSet<String>? = null
-
   fun isPostSaved(postId: String): Boolean {
-    savedPostCache ?: return false
+    // returns the post if it exists and its is_saved property is true
-    return requireNotNull(savedPostCache).contains(postId)
+    val post = lobstersDatabase.postQueries.isPostSaved(postId).executeAsOneOrNull()
+    return post != null
+  }
+
+  suspend fun getPost(postId: String): LobstersPost? = withContext(Dispatchers.IO) {
+    return@withContext lobstersDatabase.postQueries.selectPost(postId).executeAsOneOrNull()
+  }
+
+  suspend fun getSavedPosts(): List<LobstersPost> = withContext(Dispatchers.IO) {
+    return@withContext lobstersDatabase.postQueries.selectSavedPosts().executeAsList()
+  }
+
+  suspend fun addPostToDB(post: LobstersPost) = withContext(Dispatchers.IO) {
+    lobstersDatabase.postQueries.insertOrReplacePost(post)
   }
 
   suspend fun savePost(post: LobstersPost) = withContext(Dispatchers.IO) {
-    val isElementAdded = getCachedPosts().add(post.short_id)
+    if (!isPostSaved(post.short_id)) {
-    if (isElementAdded) {
       lobstersDatabase.postQueries.savePost(post.short_id)
     }
   }
 
   suspend fun removeSavedPost(post: LobstersPost) = withContext(Dispatchers.IO) {
-    val isElementRemoved = getCachedPosts().remove(post.short_id)
+    if (isPostSaved(post.short_id)) {
-    if (isElementRemoved) {
       lobstersDatabase.postQueries.removeSavedPost(post.short_id)
     }
   }
-
-  suspend fun getCachedPosts(): MutableSet<String> = withContext(Dispatchers.IO) {
-    if (savedPostCache != null) return@withContext requireNotNull(savedPostCache)
-
-    val dbPosts = lobstersDatabase.postQueries.selectSavedPosts().executeAsList()
-    savedPostCache = dbPosts.filter { it.is_saved ?: false }.map { it.short_id }.toMutableSet()
-    return@withContext requireNotNull(savedPostCache)
-  }
 }

app/src/main/java/dev/msfjarvis/lobsters/injection/DatabaseModule.kt

@@ -12,17 +12,20 @@ import dev.msfjarvis.lobsters.data.local.LobstersPost
 import dev.msfjarvis.lobsters.database.LobstersDatabase
 import dev.msfjarvis.lobsters.model.SubmitterAdapter
 import dev.msfjarvis.lobsters.model.TagsAdapter
+import javax.inject.Singleton
 
 @Module
 @InstallIn(SingletonComponent::class)
 object DatabaseModule {
 
   @Provides
+  @Singleton
   fun providesSqlDriver(@ApplicationContext context: Context): SqlDriver {
     return AndroidSqliteDriver(LobstersDatabase.Schema, context)
   }
 
   @Provides
+  @Singleton
   fun providesLobstersDatabase(sqlDriver: SqlDriver): LobstersDatabase {
     return LobstersDatabase(sqlDriver, LobstersPost.Adapter(SubmitterAdapter(), TagsAdapter()))
   }

app/src/main/java/dev/msfjarvis/lobsters/ui/main/MainActivity.kt

@@ -64,6 +64,8 @@ fun LobstersApp() {
   val savedPosts by viewModel.savedPosts.collectAsState()
   val hottestPostsListState = rememberLazyListState()
 
+  viewModel.getSavedPosts()
+
   Scaffold(
     bottomBar = {
       LobstersBottomNav(

app/src/main/java/dev/msfjarvis/lobsters/ui/posts/LobstersItem.kt

@@ -14,6 +14,10 @@ import androidx.compose.material.Surface
 import androidx.compose.material.Text
 import androidx.compose.material.ripple.rememberRipple
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
@@ -65,6 +69,8 @@ fun LobstersItem(
   onLongClick: () -> Unit,
   onSaveButtonClick: () -> Unit,
 ) {
+  var isSaved by remember { mutableStateOf(post.is_saved ?: false) }
+
   Surface(
     modifier = Modifier
       .fillMaxWidth()
@@ -121,11 +127,14 @@ fun LobstersItem(
           },
       )
       IconResource(
-        resourceId = if (post.is_saved == true) R.drawable.ic_favorite_24px else R.drawable.ic_favorite_border_24px,
+        resourceId = if (isSaved) R.drawable.ic_favorite_24px else R.drawable.ic_favorite_border_24px,
         modifier = Modifier
           .padding(8.dp)
           .clickable(
-            onClick = onSaveButtonClick,
+            onClick = {
+              onSaveButtonClick()
+              isSaved = isSaved.not()
+            },
             indication = rememberRipple(),
           )
           .constrainAs(saveButton) {

app/src/main/java/dev/msfjarvis/lobsters/ui/viewmodel/LobstersViewModel.kt

@@ -20,7 +20,7 @@ class LobstersViewModel @Inject constructor(
 ) : ViewModel() {
   private val _savedPosts = MutableStateFlow<List<LobstersPost>>(emptyList())
   val savedPosts = _savedPosts.asStateFlow()
-  val posts = Pager(PagingConfig(25)) {
+  val posts = Pager(PagingConfig(5)) {
     pagingSource
   }.flow
 
@@ -31,17 +31,25 @@ class LobstersViewModel @Inject constructor(
     }
   }
 
+  fun getSavedPosts() {
+    viewModelScope.launch {
+      lobstersRepository.getSavedPosts().forEach {
+        _savedPosts.value = _savedPosts.value + it
+      }
+    }
+  }
+
   private fun savePost(post: LobstersPost) {
     viewModelScope.launch {
       lobstersRepository.savePost(post)
-      _savedPosts.value = _savedPosts.value + post
+      _savedPosts.value = _savedPosts.value + post.copy(is_saved = true)
     }
   }
 
   private fun removeSavedPost(post: LobstersPost) {
     viewModelScope.launch {
       lobstersRepository.removeSavedPost(post)
-      _savedPosts.value = _savedPosts.value - post
+      _savedPosts.value = _savedPosts.value - post.copy(is_saved = true)
     }
   }
 }

database/src/main/sqldelight/dev/msfjarvis/lobsters/data/local/Post.sq

@@ -56,6 +56,12 @@ deleteAllPosts:
 DELETE
 FROM LobstersPost;
 
+isPostSaved:
+SELECT *
+FROM LobstersPost
+WHERE short_id = ?
+AND is_saved = 1;
+
 selectCount:
 SELECT COUNT(*)
 FROM LobstersPost;