[Emulator] has default constructor and factory to load env string

packages/dart_firebase_admin/lib/src/app/emulator.dart

@@ -3,8 +3,29 @@ part of '../app.dart';
 /// Represents a Firebase Emulator.
 /// Now for Auth and Firestore.
 class Emulator {
-  Emulator(this.host, this.port);
+  const Emulator._(this.host, this.port);
+
+  const Emulator.defaultAuth()
+      : host = '127.0.0.1',
+        port = 9099;
+
+  const Emulator.defaultFirestore()
+      : host = '127.0.0.1',
+        port = 8080;
+
+  factory Emulator.fromEnvString(String envString) {
+    final parts = envString.split(':');
+    if (parts.length != 2) {
+      throw ArgumentError.value(envString, 'envString', 'Invalid format');
+    }
+    final host = parts[0];
+    final port = int.tryParse(parts[1]);
+    if (port == null) {
+      throw ArgumentError.value(envString, 'envString', 'Invalid port');
+    }
+    return Emulator._(host, port);
+  }
 
   final String host;
   final int port;
-}
+}

packages/dart_firebase_admin/lib/src/app/firebase_admin.dart

@@ -10,8 +10,11 @@ class FirebaseAdminApp {
   final Credential credential;
 
   bool get isUsingAuthEmulator => _isUsingAuthEmulator;
+
   bool get isUsingFirestoreEmulator => _isUsingFirestoreEmulator;
+
   bool get isUsingEmulator => _isUsingAuthEmulator || _isUsingFirestoreEmulator;
+
   var _isUsingAuthEmulator = false;
   var _isUsingFirestoreEmulator = false;
 
@@ -21,25 +24,29 @@ class FirebaseAdminApp {
   Uri firestoreApiHost = Uri.https('firestore.googleapis.com', '/');
 
   /// Use the Firebase Emulator suite to run the app locally.
-  void useEmulator({Emulator? authEmulator, Emulator? firestoreEmulator}) {
+  void useEmulator({
+    Emulator authEmulator = const Emulator.defaultAuth(),
+    Emulator firestoreEmulator = const Emulator.defaultFirestore(),
+  }) {
     useAuthEmulator(emulator: authEmulator);
     useFirestoreEmulator(emulator: firestoreEmulator);
   }
 
   /// Use the Firebase Auth Emulator to run the app locally.
-  void useAuthEmulator({Emulator? emulator}) {
+  void useAuthEmulator({
+    Emulator emulator = const Emulator.defaultAuth(),
+  }) {
     _isUsingAuthEmulator = true;
-    final host = emulator?.host ?? '127.0.0.1';
-    final port = emulator?.port ?? 9099;
-    authApiHost = Uri.http('$host:$port', 'identitytoolkit.googleapis.com/');
+    authApiHost = Uri.http(
+        '${emulator.host}:${emulator.port}', 'identitytoolkit.googleapis.com/');
   }
 
   /// Use the Firebase Firestore Emulator to run the app locally.
-  void useFirestoreEmulator({Emulator? emulator}) {
+  void useFirestoreEmulator({
+    Emulator emulator = const Emulator.defaultFirestore(),
+  }) {
     _isUsingFirestoreEmulator = true;
-    final host = emulator?.host ?? '127.0.0.1';
-    final port = emulator?.port ?? 8080;
-    firestoreApiHost = Uri.http('$host:$port', '/');
+    firestoreApiHost = Uri.http('${emulator.host}:${emulator.port}', '/');
   }
 
   /// Stops the app and releases any resources associated with it.