[Android] Fix crash regression and no browser crash (#190)

* Fix crash regression and no browser crash

* Grammar

---------

Co-authored-by: Long Yang Paffrath <lypaffrath@dfn.de>

Author: Mino5531

flutter_web_auth_2/android/src/main/kotlin/com/linusu/flutter_web_auth_2/AuthenticationManagementActivity.kt

@@ -35,7 +35,7 @@ class AuthenticationManagementActivity : ComponentActivity() {
     private var authStarted: Boolean = false
     private lateinit var authenticationUri: Uri
     private var intentFlags: Int = 0
-    private lateinit var targetPackage: String
+    private var targetPackage: String? = null
     private var preferEphemeral: Boolean = false
     private lateinit var callbackScheme: String
     private var callbackHost: String? = null
@@ -107,14 +107,24 @@ class AuthenticationManagementActivity : ComponentActivity() {
             val intent = intentBuilder.build()
 
             intent.intent.addFlags(intentFlags)
-            intent.intent.setPackage(targetPackage)
+            if(targetPackage != null){
+                intent.intent.setPackage(targetPackage)
+            }
 
-            if (callbackScheme == "https" && callbackHost != null && callbackPath != null) {
-                Log.d(LOG_TAG, "Using https host and path: $callbackHost, $callbackPath")
-                intent.launch(this, authLauncher, authenticationUri, callbackHost!!, callbackPath!!)
-            } else {
-                Log.d(LOG_TAG, "Using custom scheme: $callbackScheme")
-                intent.launch(this, authLauncher, authenticationUri, callbackScheme)
+            try{
+                if (callbackScheme == "https" && callbackHost != null && callbackPath != null) {
+                    Log.d(LOG_TAG, "Using https host and path: $callbackHost, $callbackPath")
+                    intent.launch(this, authLauncher, authenticationUri, callbackHost!!, callbackPath!!)
+                } else {
+                    Log.d(LOG_TAG, "Using custom scheme: $callbackScheme")
+                    intent.launch(this, authLauncher, authenticationUri, callbackScheme)
+                }
+            } catch (e: android.content.ActivityNotFoundException){
+                Log.e(LOG_TAG,"Failed to start authentication. No browser available (Activity not found)")
+                val callback = FlutterWebAuth2Plugin.callbacks[callbackScheme]
+                callback?.error("NO_BROWSER","No valid browser available for authentication.",e.message)
+                FlutterWebAuth2Plugin.callbacks.remove(callbackScheme)
+                finish()
             }
 
             authStarted = true
@@ -129,8 +139,8 @@ class AuthenticationManagementActivity : ComponentActivity() {
 
     fun shouldUseLegacySystem(): Boolean {
 
-        if (!preferEphemeral) return false
-        val packageMajorVersion = getInstalledVersion(targetPackage)?.substringBefore(".")?.toIntOrNull() ?: 0
+        if (!preferEphemeral || targetPackage == null) return false
+        val packageMajorVersion = getInstalledVersion(targetPackage!!)?.substringBefore(".")?.toIntOrNull() ?: 0
         Log.d(LOG_TAG, "Chosen package: $targetPackage with version: $packageMajorVersion")
 
         val chromePackages = setOf(
@@ -180,7 +190,7 @@ class AuthenticationManagementActivity : ComponentActivity() {
             state.getParcelable(KEY_AUTH_URI)
         } ?: throw IllegalStateException("Authentication URI is null")
         intentFlags = state.getInt(KEY_AUTH_OPTION_INTENT_FLAGS, 0)
-        targetPackage = state.getString(KEY_AUTH_OPTION_TARGET_PACKAGE)!!
+        targetPackage = state.getString(KEY_AUTH_OPTION_TARGET_PACKAGE)
         preferEphemeral = state.getBoolean(KEY_AUTH_OPTION_PREFER_EPHEMERAL, false)
         callbackScheme = state.getString(KEY_AUTH_CALLBACK_SCHEME)!!
         callbackHost = state.getString(KEY_AUTH_CALLBACK_HOST)

flutter_web_auth_2/android/src/main/kotlin/com/linusu/flutter_web_auth_2/FlutterWebAuth2Plugin.kt

@@ -93,9 +93,9 @@ class FlutterWebAuth2Plugin(
      * 1. Custom Browser Order (if supported)
      * 2. default Browser
      * 3. Installed Browsers (if supported)
-     * 4. Chrome (last fallback)
+     * 4. null (System backup aka. some obscure browser that may work)
      */
-    private fun findTargetBrowserPackageName(options: Map<String, Any>): String {
+    private fun findTargetBrowserPackageName(options: Map<String, Any>): String? {
         val context = requireNotNull(context) { "Context is null" }
 
         val selectedPackage = (options["customTabsPackageOrder"] as? Iterable<*>)
@@ -115,8 +115,9 @@ class FlutterWebAuth2Plugin(
         // Check installed browser
         val matchedBrowser = getInstalledBrowsers().firstOrNull { isSupportCustomTabs(it) }
 
-        // Safely fall back on Chrome just in case
-        return matchedBrowser ?: PackageNames.CHROME_STABLE
+        // Don't fall back to Chrome here. It is not installed anyway because it would already be in matchedBrowser.
+        // Instead, fall back to null so we can use the system backup (if one is available).
+        return matchedBrowser
     }
 
     private fun getInstalledBrowsers(): List<String> {