Adding release signing for code magic

Author: burhanrashid52

android/app/build.gradle

@@ -14,6 +14,12 @@ if (flutterRoot == null) {
 apply plugin: 'com.android.application'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
+def keystoreProperties = new Properties()
+def keystorePropertiesFile = rootProject.file('key.properties')
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+}
+
 android {
     compileSdkVersion 29
 
@@ -30,10 +36,27 @@ android {
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
 
+    signingConfigs {
+        release {
+            if (System.getenv()["CI"]) { // CI=true is exported by Codemagic
+                storeFile file(System.getenv()["FCI_KEYSTORE_PATH"])
+                storePassword System.getenv()["FCI_KEYSTORE_PASSWORD"]
+                keyAlias System.getenv()["FCI_KEY_ALIAS"]
+                keyPassword System.getenv()["FCI_KEY_PASSWORD"]
+            } else {
+                keyAlias keystoreProperties['keyAlias']
+                keyPassword keystoreProperties['keyPassword']
+                storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
+                storePassword keystoreProperties['storePassword']
+            }
+        }
+    }
+
     buildTypes {
         release {
-            // TODO: Add your own signing config for the release build.
-            // Signing with the debug keys for now, so `flutter run --release` works.
+            signingConfig signingConfigs.release
+        }
+        debug {
             signingConfig signingConfigs.debug
         }
     }