reimplemented export process

app/common/filefunctions.cpp

@@ -75,7 +75,7 @@ QString FileFunctions::GetTempFilePath()
 {
   QString temp_path = QDir(QDir(QStandardPaths::writableLocation(QStandardPaths::TempLocation))
                            .filePath(QCoreApplication::organizationName()))
-                   .filePath(QCoreApplication::applicationName());
+      .filePath(QCoreApplication::applicationName());
 
   // Ensure it exists
   QDir(temp_path).mkpath(".");
@@ -199,4 +199,45 @@ QString FileFunctions::ReadFileAsString(const QString &filename)
   return file_data;
 }
 
+QString FileFunctions::GetSafeTemporaryFilename(const QString &original)
+{
+  int counter = 0;
+
+  QFileInfo original_info(original);
+  QString basename = original_info.baseName();
+  QString complete_suffix = original_info.completeSuffix();
+
+  // If we have a complete suffix, make sure there's a period in it
+  if (!complete_suffix.isEmpty()) {
+    complete_suffix.prepend('.');
+  }
+
+  QString temp_abs_path;
+  do {
+    temp_abs_path = original_info.dir().filePath(
+          QStringLiteral("%1.tmp%2%3").arg(basename,
+                                           QString::number(counter),
+                                           complete_suffix));
+    counter++;
+  } while (QFileInfo::exists(temp_abs_path));
+
+  return temp_abs_path;
+}
+
+bool FileFunctions::RenameFileAllowOverwrite(const QString &from, const QString &to)
+{
+  if (QFileInfo::exists(to) && !QFile::remove(to)) {
+    qCritical() << "Couldn't remove existing file" << to << "for overwrite";
+    return false;
+  }
+
+  // By this point, we can assume `to` either never existed or has now been deleted
+  if (!QFile::rename(from, to)) {
+    qCritical() << "Failed to rename file" << from << "to" << to;
+    return false;
+  }
+
+  return true;
+}
+
 OLIVE_NAMESPACE_EXIT

app/common/filefunctions.h

@@ -67,6 +67,23 @@ public:
 
   static QString ReadFileAsString(const QString& filename);
 
+  /**
+   * @brief Returns a temporary filename that can be used while writing rather than the original
+   *
+   * If overwriting a file, it's safest to write to a new file first and then only replace it at
+   * the end so that if the program crashes or the user cancels the save half way through, the
+   * original file is still intact.
+   *
+   * This function returns a slight variant of the filename provided that's guaranteed to not exist
+   * and therefore won't overwrite anything important.
+   */
+  static QString GetSafeTemporaryFilename(const QString& original);
+
+  /**
+   * @brief Renames a file from `from` to `to`, deleting `to` if such a file already exists first
+   */
+  static bool RenameFileAllowOverwrite(const QString& from, const QString& to);
+
 };