Add toFlow extensions to DocumentSnapshot and Query

Author: michgauz

firebase-firestore/ktx/ktx.gradle

@@ -51,6 +51,7 @@ dependencies {
     implementation project(':firebase-common:ktx')
     implementation project(':firebase-firestore')
     implementation 'androidx.annotation:annotation:1.1.0'
+    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.3'
     testImplementation project(':firebase-database-collection')
     testImplementation 'org.mockito:mockito-core:2.25.0'
     testImplementation 'com.fasterxml.jackson.core:jackson-databind:2.9.8'

firebase-firestore/ktx/src/main/kotlin/com/google/firebase/firestore/ktx/Firestore.kt

@@ -18,15 +18,13 @@ import androidx.annotation.Keep
 import com.google.firebase.FirebaseApp
 import com.google.firebase.components.Component
 import com.google.firebase.components.ComponentRegistrar
-import com.google.firebase.firestore.DocumentSnapshot
-import com.google.firebase.firestore.FieldPath
-import com.google.firebase.firestore.FirebaseFirestore
-import com.google.firebase.firestore.QueryDocumentSnapshot
-import com.google.firebase.firestore.QuerySnapshot
-import com.google.firebase.firestore.FirebaseFirestoreSettings
+import com.google.firebase.firestore.*
+import com.google.firebase.firestore.util.Logger
 
 import com.google.firebase.ktx.Firebase
 import com.google.firebase.platforminfo.LibraryVersionComponent
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.callbackFlow
 
 /** Returns the [FirebaseFirestore] instance of the default [FirebaseApp]. */
 val Firebase.firestore: FirebaseFirestore
@@ -163,3 +161,35 @@ class FirebaseFirestoreKtxRegistrar : ComponentRegistrar {
     override fun getComponents(): List<Component<*>> =
             listOf(LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME))
 }
+
+/**
+ * Attach a snapshotListener to a DocumentReference and use it as a coroutine flow
+ */
+fun DocumentReference.toFlow() = callbackFlow {
+    val listener = addSnapshotListener { value, error ->
+        if (value != null && value.exists()) {
+            offer(value)
+        } else if (error != null) {
+            Logger.warn("DocumentReference:flow", error.message)
+        }
+    }
+    awaitClose {
+        listener.remove()
+    }
+}
+
+/**
+ * Attach a snapshotListener to a Query and use it as a coroutine flow
+ */
+fun Query.toFlow() = callbackFlow {
+    val listener = addSnapshotListener { value, error ->
+        if (value != null) {
+            offer(value)
+        } else if (error != null) {
+            Logger.warn("Query:flow", error.message)
+        }
+    }
+    awaitClose {
+        listener.remove()
+    }
+}