fix(gui): remember last selected account after client restart

Fixes #8986

- Add ConfigFile methods to save/load last selected account identifier
- Save account id when user changes accounts (not during initialization)
- Restore last selected account on startup
- Fallback to first account if saved account was deleted
- Handle empty accounts case explicitly

Uses account()->id() as a stable identifier and prevents saving
during initialization to avoid redundant writes.

Author: harshasiddartha

src/gui/tray/usermodel.cpp

@@ -1334,7 +1334,6 @@ UserModel *UserModel::instance()
 UserModel::UserModel(QObject *parent)
     : QAbstractListModel(parent)
 {
-    // TODO: Remember selected user from last quit via settings file
     if (AccountManager::instance()->accounts().size() > 0) {
         buildUserList();
     }
@@ -1349,8 +1348,34 @@ void UserModel::buildUserList()
         auto user = AccountManager::instance()->accounts().at(i);
         addUser(user);
     }
-    if (_init) {
-        _users.first()->setCurrentUser(true);
+    if (_init && !_users.isEmpty()) {
+        // Try to restore the last selected account
+        ConfigFile cfg;
+        const auto lastSelectedAccountId = cfg.lastSelectedAccount();
+        
+        if (!lastSelectedAccountId.isEmpty()) {
+            // Find the account by id (more stable than displayName)
+            int foundIndex = -1;
+            for (int i = 0; i < _users.size(); i++) {
+                if (_users[i]->account()->id() == lastSelectedAccountId) {
+                    foundIndex = i;
+                    break;
+                }
+            }
+            
+            if (foundIndex >= 0 && foundIndex < _users.size()) {
+                setCurrentUserId(foundIndex);
+                _init = false;
+                return;
+            }
+        }
+        
+        // Fallback to first account if last selected account not found
+        setCurrentUserId(0);
+        _init = false;
+    } else if (_init && _users.isEmpty()) {
+        // No accounts available - ensure initialization is complete
+        // _currentUserId remains -1 (no account selected)
         _init = false;
     }
 }
@@ -1525,6 +1550,13 @@ void UserModel::setCurrentUserId(const int id)
         emit currentUserChanged();
     } else if (_currentUserId != id) {
         _currentUserId = id;
+        
+        // Save the last selected account identifier (but not during initialization)
+        if (!_init) {
+            ConfigFile cfg;
+            cfg.setLastSelectedAccount(_users[id]->account()->id());
+        }
+        
         emit currentUserChanged();
     }
 }

src/libsync/configfile.cpp

@@ -95,6 +95,7 @@ static const QStringList enterpriseUpdateChannelsList { QStringLiteral("stable")
 static const QString defaultEnterpriseChannel = "enterprise";
 
 static constexpr char languageC[] = "language";
+static constexpr char lastSelectedAccountC[] = "lastSelectedAccount";
 
 static constexpr int deleteFilesThresholdDefaultValue = 100;
 }
@@ -1255,6 +1256,18 @@ void ConfigFile::setLanguage(const QString& language)
     settings.setValue(QLatin1String(languageC), language);
 }
 
+QString ConfigFile::lastSelectedAccount() const
+{
+    QSettings settings(configFile(), QSettings::IniFormat);
+    return settings.value(QLatin1String(lastSelectedAccountC), QLatin1String("")).toString();
+}
+
+void ConfigFile::setLastSelectedAccount(const QString &accountIdentifier)
+{
+    QSettings settings(configFile(), QSettings::IniFormat);
+    settings.setValue(QLatin1String(lastSelectedAccountC), accountIdentifier);
+}
+
 Q_GLOBAL_STATIC(QString, g_configFileName)
 
 std::unique_ptr<QSettings> ConfigFile::settingsWithGroup(const QString &group, QObject *parent)

src/libsync/configfile.h

@@ -238,6 +238,10 @@ class OWNCLOUDSYNC_EXPORT ConfigFile
     [[nodiscard]] QString language() const;
     void setLanguage(const QString &language);
 
+    /// Store and retrieve the last selected account identifier
+    [[nodiscard]] QString lastSelectedAccount() const;
+    void setLastSelectedAccount(const QString &accountIdentifier);
+
     /**  Returns a new settings pre-set in a specific group.  The Settings will be created
          with the given parent. If no parent is specified, the caller must destroy the settings */
     static std::unique_ptr<QSettings> settingsWithGroup(const QString &group, QObject *parent = nullptr);