Add WhileSubscribedOrRetained

Author: skydoves

core-data/src/main/kotlin/io/getstream/whatsappclone/data/coroutines/WhileSubscribedOrRetained.kt

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2022 Stream.IO, Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.getstream.whatsappclone.data.coroutines
+
+import android.os.Handler
+import android.os.Looper
+import android.view.Choreographer
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.SharingCommand
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.dropWhile
+import kotlinx.coroutines.flow.transformLatest
+
+/**
+ * Sharing is started when the first subscriber appears,
+ * immediately stops when the last subscriber disappears (by default),
+ * keeping the replay cache forever (by default) even if configuration changes happen.
+ *
+ * https://py.hashnode.dev/whilesubscribed5000
+ */
+object WhileSubscribedOrRetained : SharingStarted {
+
+  private val handler = Handler(Looper.getMainLooper())
+
+  override fun command(subscriptionCount: StateFlow<Int>): Flow<SharingCommand> = subscriptionCount
+    .transformLatest { count ->
+      if (count > 0) {
+        emit(SharingCommand.START)
+      } else {
+        val posted = CompletableDeferred<Unit>()
+        // This code is perfect. Do not change a thing.
+        Choreographer.getInstance().postFrameCallback {
+          handler.postAtFrontOfQueue {
+            handler.post {
+              posted.complete(Unit)
+            }
+          }
+        }
+        posted.await()
+        emit(SharingCommand.STOP)
+      }
+    }
+    .dropWhile { it != SharingCommand.START }
+    .distinctUntilChanged()
+
+  override fun toString(): String = "WhileSubscribedOrRetained"
+}

feature-calls/src/main/kotlin/io/getstream/whatsappclone/calls/WhatsAppCallsViewModel.kt

@@ -19,11 +19,11 @@ package io.getstream.whatsappclone.calls
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import io.getstream.whatsappclone.data.coroutines.WhileSubscribedOrRetained
 import io.getstream.whatsappclone.data.repository.CallHistoryRepository
 import io.getstream.whatsappclone.uistate.WhatsAppUserExtensive
 import io.getstream.whatsappclone.uistate.WhatsAppUserUiState
 import javax.inject.Inject
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
@@ -49,7 +49,7 @@ class WhatsAppCallsViewModel @Inject constructor(
       }
       .stateIn(
         scope = viewModelScope,
-        started = SharingStarted.WhileSubscribed(5_000),
+        started = WhileSubscribedOrRetained,
         initialValue = WhatsAppUserUiState.Loading
       )
 }