Run shell on the Flatpak host

When Terminal is running on Flatpak we need to access the host
system, otherwise the app is pretty useless.

Closes: #36

src/lib/Session.cpp

@@ -35,6 +35,7 @@
 #include <QDir>
 #include <QFile>
 #include <QRegExp>
+#include <QStandardPaths>
 #include <QStringList>
 #include <QFile>
 #include <QtDebug>
@@ -330,13 +331,27 @@ void Session::run()
     // the background color is deemed dark or not
     QString backgroundColorHint = _hasDarkBackground ? "COLORFGBG=15;0" : "COLORFGBG=0;15";
 
+    QStringList environmentVars = _environment << backgroundColorHint;
+
+    // If we are running on Flatpak, we should have access to the host
+    if (!QStandardPaths::locate(QStandardPaths::RuntimeLocation, QLatin1String("flatpak-info")).isEmpty()) {
+        QStringList flatpakArgs;
+        flatpakArgs << QLatin1String("--host");
+        for (auto env : qAsConst(environmentVars))
+            flatpakArgs << QStringLiteral("--env=%1").arg(env);
+        flatpakArgs << exec;
+        exec = QLatin1String("/usr/bin/flatpak-spawn");
+        arguments = flatpakArgs;
+        environmentVars = QStringList();
+    }
+
     /* if we do all the checking if this shell exists then we use it ;)
      * Dont know about the arguments though.. maybe youll need some more checking im not sure
      * However this works on Arch and FreeBSD now.
      */
     int result = _shellProcess->start(exec,
                                       arguments,
-                                      _environment << backgroundColorHint,
+                                      environmentVars,
                                       windowId(),
                                       _addToUtmp);