app: add BackupHandler

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

app/src/main/java/dev/msfjarvis/lobsters/data/backup/BackupHandler.kt

@@ -0,0 +1,32 @@
+package dev.msfjarvis.lobsters.data.backup
+
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.adapter
+import dev.msfjarvis.lobsters.data.local.SavedPost
+import dev.msfjarvis.lobsters.database.LobstersDatabase
+import javax.inject.Inject
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+
+@OptIn(ExperimentalStdlibApi::class)
+class BackupHandler
+@Inject
+constructor(
+  private val database: LobstersDatabase,
+  moshi: Moshi,
+) {
+  private val adapter = moshi.adapter<List<SavedPost>>()
+
+  suspend fun exportSavedPosts(): String {
+    val posts =
+      withContext(Dispatchers.IO) { database.savedPostQueries.selectAllPosts().executeAsList() }
+    return adapter.toJson(posts)
+  }
+
+  suspend fun importSavedPosts(json: String) {
+    withContext(Dispatchers.IO) {
+      val posts = requireNotNull(adapter.fromJson(json))
+      database.transaction { posts.forEach { database.savedPostQueries.insertOrReplacePost(it) } }
+    }
+  }
+}

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

@@ -0,0 +1,21 @@
+package dev.msfjarvis.lobsters.injection
+
+import com.squareup.moshi.Moshi
+import dagger.Module
+import dagger.Provides
+import dagger.hilt.InstallIn
+import dagger.hilt.android.components.ActivityComponent
+import dev.msfjarvis.lobsters.data.backup.BackupHandler
+import dev.msfjarvis.lobsters.database.LobstersDatabase
+
+@Module
+@InstallIn(ActivityComponent::class)
+object BackupModule {
+  @Provides
+  fun provideBackupHandler(
+    database: LobstersDatabase,
+    moshi: Moshi,
+  ): BackupHandler {
+    return BackupHandler(database, moshi)
+  }
+}