SettingsComponent: remember the oldest installed version

This uses separate code via QSettings, so the value survives config
version bumps or user deletions. The user has no disadvantages from
this, so the separate settings should not cause any issues.

To make sure the legacy detection mechanism works, we must sure that the
normal config file is absolutely not written before this code is run,
thus the change in saveSettings().

src/settings/SettingsComponent.cpp

@@ -11,8 +11,12 @@
 #include <QJsonObject>
 #include <QJsonArray>
 #include <QList>
+#include <QSettings>
 #include "input/InputComponent.h"
 #include "system/SystemComponent.h"
+#include "Version.h"
+
+#define OLDEST_PREVIOUS_VERSION_KEY "oldestPreviousVersion"
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 SettingsComponent::SettingsComponent(QObject *parent) : ComponentBase(parent), m_settingsVersion(-1)
@@ -203,6 +207,12 @@ void SettingsComponent::loadConf(const QString& path, bool storage)
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 void SettingsComponent::saveSettings()
 {
+  if (m_oldestPreviousVersion.isEmpty())
+  {
+    QLOG_ERROR() << "Not writing settings: uninitialized.\n";
+    return;
+  }
+
   QVariantMap sections;
 
   for(SettingsSection* section : m_sections.values())
@@ -569,6 +579,9 @@ bool SettingsComponent::componentInitialize()
   if (!loadDescription())
     return false;
 
+  // Must be called before we possibly write the config file.
+  setupVersion();
+
   load();
 
   // add our AudioSettingsController that will inspect audio settings and react.
@@ -585,6 +598,25 @@ bool SettingsComponent::componentInitialize()
   return true;
 }
 
+/////////////////////////////////////////////////////////////////////////////////////////
+void SettingsComponent::setupVersion()
+{
+  QSettings settings("Plex", "Plex Media Player");
+  m_oldestPreviousVersion = settings.value(OLDEST_PREVIOUS_VERSION_KEY).toString();
+  if (m_oldestPreviousVersion.isEmpty())
+  {
+    // Version key was not present. It could still be a pre-1.1 PMP install,
+    // so here we try to find out whether this is the very first install, or
+    // if an older one exists.
+    QFile configFile(Paths::dataDir("plexmediaplayer.conf"));
+    if (configFile.exists())
+      m_oldestPreviousVersion = "legacy";
+    else
+      m_oldestPreviousVersion = Version::GetVersionString();
+    settings.setValue(OLDEST_PREVIOUS_VERSION_KEY, m_oldestPreviousVersion);
+  }
+}
+
 /////////////////////////////////////////////////////////////////////////////////////////
 void SettingsComponent::setUserRoleList(const QStringList& userRoles)
 {

src/settings/SettingsComponent.h

@@ -75,6 +75,11 @@ public:
   //
   static bool resetAndSaveOldConfiguration();
 
+  QString oldestPreviousVersion() const
+  {
+    return m_oldestPreviousVersion;
+  }
+
 private:
   explicit SettingsComponent(QObject *parent = nullptr);
   bool loadDescription();
@@ -82,12 +87,15 @@ private:
   int platformMaskFromObject(const QJsonObject& object);
   Platform platformFromString(const QString& platformString);
   void saveSection(SettingsSection* section);
+  void setupVersion();
 
   QMap<QString, SettingsSection*> m_sections;
 
   int m_settingsVersion;
   int m_sectionIndex;
 
+  QString m_oldestPreviousVersion;
+
   void loadConf(const QString& path, bool storage);
 };