[UNTESTED] Support a lack of MANAGE_DOCUMENTS permission

When `android.permission.MANAGE_DOCUMENTS` is not granted, Seedvault
prompts to select a storage location. Do not insist on resolving the
storage's actual root, as it will likely (or perhaps always) fail.
Use a fake storage root as is done for USB and app-based options.

Known issues:
* Selected location is assumed not to be USB and not to require
  network access in its storage options.

Change-Id: I357b4c68673d71c087be41e9c94c2841c1d6658e

app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageActivity.kt

@@ -35,7 +35,9 @@ class StorageActivity : BackupActivity() {
             val authority = uri.authority ?: throw AssertionError("No authority in $uri")
             val storageRoot = StorageRootResolver.getStorageRoots(this, authority).getOrNull(0)
             if (storageRoot == null) {
-                viewModel.onUriPermissionResultReceived(null)
+                viewModel.onSafOptionChosen(
+                    StorageRootResolver.getFakeStorageRootForUri(this, uri))
+                viewModel.onUriPermissionResultReceived(uri)
             } else {
                 viewModel.onSafOptionChosen(storageRoot)
                 viewModel.onUriPermissionResultReceived(uri)

app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageRootResolver.kt

@@ -3,6 +3,7 @@ package com.stevesoltys.seedvault.ui.storage
 import android.content.Context
 import android.database.Cursor
 import android.graphics.drawable.Drawable
+import android.net.Uri
 import android.os.UserHandle
 import android.provider.DocumentsContract
 import android.provider.DocumentsContract.Root.COLUMN_AVAILABLE_BYTES
@@ -57,6 +58,21 @@ internal object StorageRootResolver {
         return roots
     }
 
+    fun getFakeStorageRootForUri(context: Context, uri: Uri): SafOption {
+        return SafOption(
+            authority = AUTHORITY_STORAGE,
+            rootId = "fake",
+            documentId = "fake",
+            // TODO: Use something other than the USB icon?
+            icon = getIcon(context, AUTHORITY_STORAGE, "usb", 0),
+            title = context.getString(R.string.storage_user_selected_location_title),
+            summary = context.getString(R.string.storage_user_selected_location_summary),
+            availableBytes = null,
+            isUsb = false, // TODO: Check this if possible instead of forcing false
+            requiresNetwork = false, // TODO: Check this if possible instead of forcing false
+        )
+    }
+
     private fun getStorageRoot(context: Context, authority: String, cursor: Cursor): SafOption? {
         val flags = cursor.getInt(COLUMN_FLAGS)
         val supportsCreate = flags and FLAG_SUPPORTS_CREATE != 0

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

@@ -58,6 +58,8 @@
     <string name="storage_fragment_restore_title">Where to find your backups?</string>
     <string name="storage_fragment_warning">People with access to your storage location can learn which apps you use, but do not get access to the apps\' data.</string>
     <string name="storage_fragment_warning_delete">Existing backups in this location will be deleted.</string>
+    <string name="storage_user_selected_location_title">User-chosen location</string>
+    <string name="storage_user_selected_location_summary">Chosen using the folder browser</string>
     <string name="storage_fake_drive_title">USB flash drive</string>
     <string name="storage_fake_drive_summary">Needs to be plugged in</string>
     <string name="storage_available_bytes"><xliff:g example="1 GB" id="size">%1$s</xliff:g> free</string>