app: add support for fetching newest posts

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

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

@@ -0,0 +1,33 @@
+package dev.msfjarvis.lobsters.data.remote
+
+import androidx.paging.PagingSource
+import androidx.paging.PagingState
+import dev.msfjarvis.lobsters.data.repo.LobstersRepository
+import dev.msfjarvis.lobsters.model.LobstersPost
+
+class NewestPostsPagingSource constructor(
+  private val lobstersRepository: LobstersRepository,
+) : PagingSource<Int, LobstersPost>() {
+
+  override suspend fun load(params: LoadParams<Int>): LoadResult<Int, LobstersPost> {
+    return try {
+      val page = params.key ?: 1
+      // Update cache before fetching a list.
+      // This is done to make sure that we can update the isSaved status of incoming posts.
+      lobstersRepository.updateCache()
+      val posts = lobstersRepository.fetchNewestPosts(page)
+
+      LoadResult.Page(
+        data = posts,
+        prevKey = if (page == 1) null else page - 1,
+        nextKey = page.plus(1)
+      )
+    } catch (e: Exception) {
+      LoadResult.Error(e)
+    }
+  }
+
+  override fun getRefreshKey(state: PagingState<Int, LobstersPost>): Int {
+    return state.pages.size + 1
+  }
+}

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

@@ -30,6 +30,10 @@ class LobstersRepository constructor(
     return@withContext lobstersApi.getHottestPosts(page)
   }
 
+  suspend fun fetchNewestPosts(page: Int): List<LobstersPost> = withContext(Dispatchers.IO) {
+    return@withContext lobstersApi.getNewestPosts(page)
+  }
+
   // https://issuetracker.google.com/issues/181221325
   @Suppress("NewApi")
   suspend fun updateCache() {

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

@@ -9,6 +9,7 @@ import dagger.hilt.android.lifecycle.HiltViewModel
 import dev.msfjarvis.lobsters.data.local.SavedPost
 import dev.msfjarvis.lobsters.data.preferences.ClawPreferences
 import dev.msfjarvis.lobsters.data.remote.HottestPostsPagingSource
+import dev.msfjarvis.lobsters.data.remote.NewestPostsPagingSource
 import dev.msfjarvis.lobsters.data.repo.LobstersRepository
 import javax.inject.Inject
 import kotlinx.coroutines.flow.Flow
@@ -28,7 +29,11 @@ class LobstersViewModel @Inject constructor(
   val hottestPosts = Pager(PagingConfig(25)) {
     HottestPostsPagingSource(lobstersRepository).also { hottestPostsPagingSource = it }
   }.flow.cachedIn(viewModelScope)
+  val newestPosts = Pager(PagingConfig(25)) {
+    NewestPostsPagingSource(lobstersRepository).also { newestPostsPagingSource = it }
+  }.flow.cachedIn(viewModelScope)
   private var hottestPostsPagingSource: HottestPostsPagingSource? = null
+  private var newestPostsPagingSource: NewestPostsPagingSource? = null
 
   init {
     lobstersRepository.isCacheReady.onEach { ready ->
@@ -50,6 +55,10 @@ class LobstersViewModel @Inject constructor(
     hottestPostsPagingSource?.invalidate()
   }
 
+  fun reloadNewestPosts() {
+    newestPostsPagingSource?.invalidate()
+  }
+
   fun toggleSave(post: SavedPost) {
     viewModelScope.launch {
       val isSaved = lobstersRepository.isPostSaved(post.shortId)