From a2c058877a9a10cca275330b484fd371cdf8a7ed Mon Sep 17 00:00:00 2001
From: Aditya Wasan <adityawasan55@gmail.com>
Date: Sun, 31 Jan 2021 15:42:39 +0530
Subject: [PATCH] src: add an in-memory map to cache db posts

Signed-off-by: Aditya Wasan <adityawasan55@gmail.com>
---
 .../lobsters/data/repo/LobstersRepository.kt  | 45 ++++++++++++++-----
 .../lobsters/ui/main/MainActivity.kt          |  2 -
 .../ui/viewmodel/LobstersViewModel.kt         | 21 +++------
 3 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/app/src/main/java/dev/msfjarvis/lobsters/data/repo/LobstersRepository.kt b/app/src/main/java/dev/msfjarvis/lobsters/data/repo/LobstersRepository.kt
index 8285df9d..af3c920f 100644
--- a/app/src/main/java/dev/msfjarvis/lobsters/data/repo/LobstersRepository.kt
+++ b/app/src/main/java/dev/msfjarvis/lobsters/data/repo/LobstersRepository.kt
@@ -2,35 +2,56 @@ package dev.msfjarvis.lobsters.data.repo
 
 import dev.msfjarvis.lobsters.data.local.LobstersPost
 import dev.msfjarvis.lobsters.database.LobstersDatabase
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 import javax.inject.Inject
 
 class LobstersRepository @Inject constructor(private val lobstersDatabase: LobstersDatabase) {
 
+  private val savedPostsCache: MutableMap<String, LobstersPost> = mutableMapOf()
+  private val coroutineScope = CoroutineScope(Job() + Dispatchers.IO)
+
+  init {
+    coroutineScope.launch {
+      getAllPosts().forEach {
+        savedPostsCache.putIfAbsent(it.short_id, it)
+      }
+    }
+  }
+
   fun isPostSaved(postId: String): Boolean {
-    val post = lobstersDatabase.postQueries.isPostSaved(postId).executeAsOneOrNull()
-    return post != null
+    return savedPostsCache.containsKey(postId)
   }
 
-  suspend fun getPost(postId: String): LobstersPost? = withContext(Dispatchers.IO) {
+  fun getPostFromCache(postId: String): LobstersPost? {
+    return savedPostsCache[postId]
+  }
+
+  fun getAllPostsFromCache(): List<LobstersPost> {
+    return savedPostsCache.values.toList()
+  }
+
+  private 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()
+  private suspend fun getAllPosts(): List<LobstersPost> = withContext(Dispatchers.IO) {
+    return@withContext lobstersDatabase.postQueries.selectAllPosts().executeAsList()
   }
 
-  suspend fun addPostToDB(post: LobstersPost) = withContext(Dispatchers.IO) {
-    lobstersDatabase.postQueries.insertOrReplacePost(post)
-  }
-
-  suspend fun savePost(post: LobstersPost) = withContext(Dispatchers.IO) {
+  suspend fun addPost(post: LobstersPost) = withContext(Dispatchers.IO) {
+    if (!savedPostsCache.containsKey(post.short_id)) {
+      savedPostsCache.putIfAbsent(post.short_id, post)
       lobstersDatabase.postQueries.insertOrReplacePost(post.copy(is_saved = true))
+    }
   }
 
-  suspend fun removeSavedPost(post: LobstersPost) = withContext(Dispatchers.IO) {
-    if (isPostSaved(post.short_id)) {
+  suspend fun removePost(post: LobstersPost) = withContext(Dispatchers.IO) {
+    if (savedPostsCache.containsKey(post.short_id)) {
+      savedPostsCache.remove(post.short_id)
       lobstersDatabase.postQueries.removeSavedPost(post.short_id)
     }
   }
diff --git a/app/src/main/java/dev/msfjarvis/lobsters/ui/main/MainActivity.kt b/app/src/main/java/dev/msfjarvis/lobsters/ui/main/MainActivity.kt
index ade5f6f2..ec54d98f 100644
--- a/app/src/main/java/dev/msfjarvis/lobsters/ui/main/MainActivity.kt
+++ b/app/src/main/java/dev/msfjarvis/lobsters/ui/main/MainActivity.kt
@@ -64,8 +64,6 @@ fun LobstersApp() {
   val savedPosts by viewModel.savedPosts.collectAsState()
   val hottestPostsListState = rememberLazyListState()
 
-  viewModel.getSavedPosts()
-
   Scaffold(
     bottomBar = {
       LobstersBottomNav(
diff --git a/app/src/main/java/dev/msfjarvis/lobsters/ui/viewmodel/LobstersViewModel.kt b/app/src/main/java/dev/msfjarvis/lobsters/ui/viewmodel/LobstersViewModel.kt
index 5e996b6f..d2e14d75 100644
--- a/app/src/main/java/dev/msfjarvis/lobsters/ui/viewmodel/LobstersViewModel.kt
+++ b/app/src/main/java/dev/msfjarvis/lobsters/ui/viewmodel/LobstersViewModel.kt
@@ -17,12 +17,11 @@ import javax.inject.Inject
 
 @HiltViewModel
 class LobstersViewModel @Inject constructor(
-  private val pagingSource: LobstersPagingSource,
   private val lobstersRepository: LobstersRepository,
   private val lobstersApi: LobstersApi,
 ) : ViewModel() {
-  private val _savedPosts = MutableStateFlow<List<LobstersPost>>(emptyList())
   private lateinit var source: LobstersPagingSource
+  private val _savedPosts = MutableStateFlow(lobstersRepository.getAllPostsFromCache())
   val savedPosts = _savedPosts.asStateFlow()
   val posts = Pager(PagingConfig(25)) {
     source = LobstersPagingSource(lobstersApi, lobstersRepository)
@@ -37,29 +36,21 @@ class LobstersViewModel @Inject constructor(
     }
   }
 
-  fun getSavedPosts() {
-    viewModelScope.launch {
-      lobstersRepository.getSavedPosts().forEach {
-        _savedPosts.value = _savedPosts.value + it
-      }
-    }
-  }
-
-  fun invalidateSource() {
+  private fun invalidateSource() {
     source.invalidate()
   }
 
   private fun savePost(post: LobstersPost) {
     viewModelScope.launch {
-      lobstersRepository.savePost(post)
-      _savedPosts.value = _savedPosts.value + post.copy(is_saved = true)
+      lobstersRepository.addPost(post)
+      _savedPosts.value = lobstersRepository.getAllPostsFromCache()
     }
   }
 
   private fun removeSavedPost(post: LobstersPost) {
     viewModelScope.launch {
-      lobstersRepository.removeSavedPost(post)
-      _savedPosts.value = _savedPosts.value - post.copy(is_saved = true)
+      lobstersRepository.removePost(post)
+      _savedPosts.value = lobstersRepository.getAllPostsFromCache()
     }
   }
 }