Merge pull request #31 from msfjarvis/offline-cache

Set up offline caching and no posts state

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

@@ -4,6 +4,9 @@ import android.os.Bundle
 import androidx.activity.viewModels
 import androidx.appcompat.app.AppCompatActivity
 import androidx.compose.foundation.Text
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.lazy.LazyColumnForIndexed
 import androidx.compose.material.Scaffold
 import androidx.compose.material.TopAppBar
@@ -11,10 +14,13 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Providers
 import androidx.compose.runtime.ambientOf
 import androidx.compose.runtime.collectAsState
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.setContent
 import androidx.compose.ui.res.stringResource
 import dagger.hilt.android.AndroidEntryPoint
 import dev.msfjarvis.lobsters.api.LobstersApi
+import dev.msfjarvis.lobsters.compose.utils.IconResource
 import dev.msfjarvis.lobsters.data.LobstersViewModel
 import dev.msfjarvis.lobsters.ui.LobstersItem
 import dev.msfjarvis.lobsters.ui.LobstersTheme
@@ -52,15 +58,26 @@ fun LobstersApp(
   Scaffold(
     topBar = { TopAppBar({ Text(text = stringResource(R.string.app_name)) }) },
     bodyContent = {
-      LazyColumnForIndexed(state.value) { index, item ->
-        if (lastIndex == index) {
-          viewModel.getMorePosts()
+      if (state.value.isEmpty()) {
+        Column(
+          modifier = Modifier.fillMaxSize(),
+          verticalArrangement = Arrangement.Center,
+          horizontalAlignment = Alignment.CenterHorizontally,
+        ) {
+          IconResource(R.drawable.ic_sync_problem_24px)
+          Text(stringResource(R.string.nothing_to_see_here))
+        }
+      } else {
+        LazyColumnForIndexed(state.value) { index, item ->
+          if (lastIndex == index) {
+            viewModel.getMorePosts()
+          }
+          LobstersItem(
+            item,
+            linkOpenAction = { post -> urlLauncher.launch(post.url) },
+            commentOpenAction = { post -> urlLauncher.launch(post.commentsUrl) },
+          )
         }
-        LobstersItem(
-          item,
-          linkOpenAction = { post -> urlLauncher.launch(post.url) },
-          commentOpenAction = { post -> urlLauncher.launch(post.commentsUrl) },
-        )
       }
     }
   )

app/src/main/java/dev/msfjarvis/lobsters/data/LobstersViewModel.kt

@@ -4,27 +4,44 @@ import androidx.hilt.lifecycle.ViewModelInject
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dev.msfjarvis.lobsters.api.LobstersApi
+import dev.msfjarvis.lobsters.data.source.PostsDatabase
 import dev.msfjarvis.lobsters.model.LobstersPost
+import kotlinx.coroutines.CoroutineExceptionHandler
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.launch
-
+import java.net.UnknownHostException
 
 class LobstersViewModel @ViewModelInject constructor(
   private val lobstersApi: LobstersApi,
+  database: PostsDatabase,
 ) : ViewModel() {
   private var apiPage = 1
   private val _posts = MutableStateFlow<List<LobstersPost>>(emptyList())
+  private val dao = database.postsDao()
+  private val coroutineExceptionHandler = CoroutineExceptionHandler { _, throwable ->
+    when (throwable) {
+      // Swallow UHE since that happens when there is no internet and we'll just rely on our cache
+      is UnknownHostException -> {}
+      else -> throw throwable
+    }
+  }
   val posts: StateFlow<List<LobstersPost>> get() = _posts
 
   init {
+    viewModelScope.launch {
+      dao.loadPosts().collectLatest { _posts.value = it }
+    }
     getMorePosts()
   }
 
   fun getMorePosts() {
-    viewModelScope.launch {
-      _posts.value += lobstersApi.getHottestPosts(apiPage)
+    viewModelScope.launch(coroutineExceptionHandler) {
+      val newPosts = lobstersApi.getHottestPosts(apiPage)
+      _posts.value += newPosts
       apiPage += 1
+      dao.insertPosts(*_posts.value.toTypedArray())
     }
   }
 }

app/src/main/res/drawable/ic_sync_problem_24px.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+  <path
+      android:fillColor="#FF000000"
+      android:pathData="M3,12c0,2.21 0.91,4.2 2.36,5.64l-1.51,1.51c-0.31,0.31 -0.09,0.85 0.36,0.85L8.5,20c0.28,0 0.5,-0.22 0.5,-0.5v-4.29c0,-0.45 -0.54,-0.67 -0.85,-0.35l-1.39,1.39C5.68,15.15 5,13.66 5,12c0,-2.39 1.4,-4.46 3.43,-5.42 0.34,-0.16 0.57,-0.47 0.57,-0.84v-0.19c0,-0.68 -0.71,-1.11 -1.32,-0.82C4.92,5.99 3,8.77 3,12zM11,17h2v-2h-2v2zM19.79,4L15.5,4c-0.28,0 -0.5,0.22 -0.5,0.5v4.29c0,0.45 0.54,0.67 0.85,0.35l1.39,-1.39C18.32,8.85 19,10.34 19,12c0,2.39 -1.4,4.46 -3.43,5.42 -0.34,0.16 -0.57,0.47 -0.57,0.84v0.18c0,0.68 0.71,1.11 1.32,0.82C19.08,18.01 21,15.23 21,12c0,-2.21 -0.91,-4.2 -2.36,-5.64l1.51,-1.51c0.31,-0.31 0.09,-0.85 -0.36,-0.85zM12,13c0.55,0 1,-0.45 1,-1L13,8c0,-0.55 -0.45,-1 -1,-1s-1,0.45 -1,1v4c0,0.55 0.45,1 1,1z"/>
+</vector>

app/src/main/res/values/strings.xml

@@ -1,3 +1,4 @@
 <resources>
     <string name="app_name">lobste.rs</string>
-</resources>
+    <string name="nothing_to_see_here">Nothing to see here…</string>
+</resources>

data/src/main/java/dev/msfjarvis/lobsters/data/source/PostsDao.kt

@@ -3,6 +3,7 @@ package dev.msfjarvis.lobsters.data.source
 import androidx.room.Dao
 import androidx.room.Delete
 import androidx.room.Insert
+import androidx.room.OnConflictStrategy
 import androidx.room.Query
 import androidx.room.Transaction
 import dev.msfjarvis.lobsters.data.model.LobstersEntity
@@ -19,7 +20,7 @@ abstract class PostsDao {
     insertPosts(posts.map { LobstersEntity(it) })
   }
 
-  @Insert
+  @Insert(onConflict = OnConflictStrategy.IGNORE)
   protected abstract suspend fun insertPosts(posts: List<LobstersEntity>)
 
   @Transaction