save selection to file if above threshold

bigtext.py

@@ -238,17 +238,26 @@ class InnerBigText(QWidget):
                 you_sure.setStandardButtons(QMessageBox.StandardButton.Cancel)
                 you_sure.addButton(QPushButton(self.tr("Copy {0} to Clipboard").format(bytes_human_readable)),
                                    QMessageBox.ButtonRole.AcceptRole)
-                # TODO add save dialog
-                # you_sure.addButton(QPushButton(self.tr("Write to File")), QMessageBox.ButtonRole.YesRole)
+                you_sure.addButton(QPushButton(self.tr("Write to File")), QMessageBox.ButtonRole.YesRole)
                 you_sure.setDefaultButton(QMessageBox.StandardButton.Cancel)
                 result = you_sure.exec()
-                if result != QMessageBox.StandardButton.Yes:
+                if result == 1:  # second custom button has the number 1
+                    dialog = QFileDialog(self)
+                    (selected_file, _filter) = dialog.getSaveFileName(
+                        caption=self.tr("Save File"),
+                        directory=os.path.dirname(self.model.get_file())
+                    )
+                    if selected_file:
+                        self.model.write_range(start, end, selected_file)
+                    return
+
+                if result == QMessageBox.StandardButton.Cancel.value:
                     # abort
                     return
 
-            selected_text = self.model.read_range(start, end)
-            cb = QApplication.clipboard()
-            cb.setText(selected_text)
+                selected_text = self.model.read_range(start, end)
+                cb = QApplication.clipboard()
+                cb.setText(selected_text)
 
     def paintEvent(self, event: QPaintEvent) -> None:
         # print("paintEvent")

logFileModel.py

@@ -56,6 +56,18 @@ class LogFileModel:
                 bytes = f.read(end_byte - start_byte)
                 return bytes.decode("utf8", errors="ignore")
 
+    def write_range(self, start_byte: int, end_byte: int, file: str):
+        print("write range: %d - %d -> %s" % (start_byte, end_byte, file))
+        with self._lock, open(self._file, 'rb') as source, open(file, "w+b") as target:
+            offset = start_byte
+            source.seek(offset)
+            while offset < end_byte:
+                new_offset = min(offset + 1024 * 1024, end_byte)
+                buffer_size = new_offset - offset
+                buffer = source.read(buffer_size)
+                target.write(buffer)
+                offset = new_offset
+
     def data(self, byte_offset, scroll_lines, lines) -> List[Line]:
         # print("data(%s, %s, %s)" % (byte_offset, scroll_lines, lines))
         lines_before_offset: List[Line] = []