show notice when camera permission rejected

app/src/main/java/sh/sar/basedbank/ui/home/QrScannerActivity.kt

@@ -7,7 +7,9 @@ import android.content.pm.PackageManager
 import android.graphics.Bitmap
 import android.graphics.BitmapFactory
 import android.graphics.Rect
+import android.net.Uri
 import android.os.Bundle
+import android.provider.Settings
 import android.widget.Toast
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.appcompat.app.AppCompatActivity
@@ -19,12 +21,14 @@ import androidx.camera.core.resolutionselector.ResolutionSelector
 import androidx.camera.core.resolutionselector.ResolutionStrategy
 import androidx.camera.lifecycle.ProcessCameraProvider
 import androidx.core.content.ContextCompat
+import com.google.android.material.dialog.MaterialAlertDialogBuilder
 import de.markusfisch.android.zxingcpp.ZxingCpp
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import sh.sar.basedbank.R
 import sh.sar.basedbank.databinding.ActivityQrScannerBinding
 import java.util.concurrent.Executors
 
@@ -45,9 +49,11 @@ class QrScannerActivity : AppCompatActivity() {
         textMode = ZxingCpp.TextMode.PLAIN
     )
 
+    private var cameraStarted = false
+
     private val permissionLauncher = registerForActivityResult(
         ActivityResultContracts.RequestPermission()
-    ) { granted -> if (granted) startCamera() else finish() }
+    ) { granted -> if (granted) startCamera() else showPermissionRationale() }
 
     private val pickImageLauncher = registerForActivityResult(
         ActivityResultContracts.GetContent()
@@ -89,7 +95,30 @@ class QrScannerActivity : AppCompatActivity() {
         else permissionLauncher.launch(Manifest.permission.CAMERA)
     }
 
+    override fun onResume() {
+        super.onResume()
+        if (!cameraStarted && ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
+            == PackageManager.PERMISSION_GRANTED
+        ) startCamera()
+    }
+
+    private fun showPermissionRationale() {
+        MaterialAlertDialogBuilder(this)
+            .setTitle(R.string.qr_camera_permission_title)
+            .setMessage(R.string.qr_camera_permission_message)
+            .setNegativeButton(R.string.cancel) { dialog, _ -> dialog.dismiss() }
+            .setPositiveButton(R.string.go_to_settings) { _, _ ->
+                startActivity(
+                    Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS).apply {
+                        data = Uri.fromParts("package", packageName, null)
+                    }
+                )
+            }
+            .show()
+    }
+
     private fun startCamera() {
+        cameraStarted = true
         val future = ProcessCameraProvider.getInstance(this)
         future.addListener({
             val provider = try {

app/src/main/res/values/strings.xml

@@ -159,6 +159,9 @@
     <string name="transfer_scan_qr">Scan QR</string>
     <string name="qr_pick_image">Pick image</string>
     <string name="transfer_qr_invalid">Invalid or unsupported QR code</string>
+    <string name="qr_camera_permission_title">Camera permission required</string>
+    <string name="qr_camera_permission_message">Camera access is needed to scan QR codes. Please grant the permission in Settings.</string>
+    <string name="go_to_settings">Go to Settings</string>
     <string name="transfer_select_source_first">Select a source account first</string>
     <string name="transfer_enter_account_first">Enter an account number first</string>
     <string name="transfer_account_not_found">Account not found</string>