PermissionUtil: remember permission requested when requesting media storage permissions

For devices under SDK 30, permission was asked on every startup, which is not desired, and is different from the
behaviour above SDK 30. This fixes that.

Signed-off-by: Álvaro Brey <alvaro.brey@nextcloud.com>

app/src/main/java/com/owncloud/android/utils/PermissionUtil.kt

@@ -131,6 +131,7 @@ object PermissionUtil {
                         requestStoragePermission(
                             activity,
                             Manifest.permission.READ_EXTERNAL_STORAGE,
+                            permissionRequired,
                             viewThemeUtils
                         )
                     }
@@ -138,6 +139,7 @@ object PermissionUtil {
                 else -> requestStoragePermission(
                     activity,
                     Manifest.permission.WRITE_EXTERNAL_STORAGE,
+                    permissionRequired,
                     viewThemeUtils
                 )
             }
@@ -151,33 +153,40 @@ object PermissionUtil {
     private fun requestStoragePermission(
         activity: Activity,
         permission: String,
+        permissionRequired: Boolean,
         viewThemeUtils: ViewThemeUtils
     ) {
+        val preferences: AppPreferences = AppPreferencesImpl.fromContext(activity)
+        val shouldRequestPermission = !preferences.isStoragePermissionRequested || permissionRequired
+
         fun doRequest() {
             ActivityCompat.requestPermissions(
                 activity,
                 arrayOf(permission),
                 PERMISSIONS_EXTERNAL_STORAGE
             )
+            preferences.isStoragePermissionRequested = true
         }
 
-        // Check if we should show an explanation
-        if (shouldShowRequestPermissionRationale(activity, permission)) {
-            // Show explanation to the user and then request permission
-            Snackbar
-                .make(
-                    activity.findViewById(android.R.id.content),
-                    R.string.permission_storage_access,
-                    Snackbar.LENGTH_INDEFINITE
-                )
-                .setAction(R.string.common_ok) {
-                    doRequest()
-                }
-                .also { viewThemeUtils.material.themeSnackbar(it) }
-                .show()
-        } else {
-            // No explanation needed, request the permission.
-            doRequest()
+        if (shouldRequestPermission) {
+            // Check if we should show an explanation
+            if (shouldShowRequestPermissionRationale(activity, permission)) {
+                // Show explanation to the user and then request permission
+                Snackbar
+                    .make(
+                        activity.findViewById(android.R.id.content),
+                        R.string.permission_storage_access,
+                        Snackbar.LENGTH_INDEFINITE
+                    )
+                    .setAction(R.string.common_ok) {
+                        doRequest()
+                    }
+                    .also { viewThemeUtils.material.themeSnackbar(it) }
+                    .show()
+            } else {
+                // No explanation needed, request the permission.
+                doRequest()
+            }
         }
     }
 
@@ -228,6 +237,7 @@ object PermissionUtil {
                             requestStoragePermission(
                                 activity,
                                 Manifest.permission.READ_EXTERNAL_STORAGE,
+                                permissionRequired,
                                 viewThemeUtils
                             )
                         }