refactor(connection): harden preserved_connections merging and reduce duplication

- Guard against empty strings and duplicate entries in preserved_connections
  by skipping falsy values and updating auto_discovered after each append,
  preventing ("", "") tuples and redundant entries in the connection list
- Widen preserved_connections type from list[str] to Sequence[str] across
  protocol, facade and connection manager so callers can pass any iterable
  without forcing list materialisation
- Extract duplicated store_connection + cache-update logic from
  add_connection() and reconnect() into _persist_and_cache_connection(),
  centralising edge-case handling in a single place

Author: amilcarlucas

ardupilot_methodic_configurator/backend_flightcontroller.py

@@ -9,6 +9,7 @@
 """
 
 from argparse import ArgumentParser
+from collections.abc import Sequence
 from logging import info as logging_info
 from logging import warning as logging_warning
 from os import path as os_path
@@ -321,7 +322,7 @@ def reset_and_reconnect(
     def discover_connections(
         self,
         progress_callback: Optional[Callable[[int, int], None]] = None,
-        preserved_connections: Optional[list[str]] = None,
+        preserved_connections: Optional[Sequence[str]] = None,
     ) -> None:
         """Discover available connections - delegates to connection manager."""
         self._connection_manager.discover_connections(

ardupilot_methodic_configurator/backend_flightcontroller_connection.py

@@ -9,6 +9,7 @@
 """
 
 import contextlib
+from collections.abc import Sequence
 from logging import debug as logging_debug
 from logging import error as logging_error
 from logging import info as logging_info
@@ -152,7 +153,7 @@ def __init__(  # pylint: disable=too-many-arguments, too-many-positional-argumen
     def discover_connections(
         self,
         progress_callback: Optional[Callable[[int, int], None]] = None,
-        preserved_connections: Optional[list[str]] = None,
+        preserved_connections: Optional[Sequence[str]] = None,
     ) -> None:
         """
         Discover all available connections (serial and network ports).
@@ -162,7 +163,7 @@ def discover_connections(
 
         Args:
             progress_callback: Optional callback for progress updates. Signature: callback(current, total)
-            preserved_connections: Optional list of connection strings (e.g. from persistent history)
+            preserved_connections: Optional sequence of connection strings (e.g. from persistent history)
                 that should always appear in the available connections list even when not auto-discovered.
                 The caller (frontend) is responsible for supplying these so the backend stays
                 free of any dependency on the settings/filesystem layer.
@@ -187,8 +188,13 @@ def discover_connections(
         if preserved_connections:
             auto_discovered = {t[0] for t in self._connection_tuples}
             for conn in preserved_connections:
+                # Skip falsy/empty connection identifiers
+                if not conn:
+                    continue
                 if conn not in auto_discovered:
                     self._connection_tuples.append((conn, conn))
+                    # Track newly added preserved connections to avoid duplicates
+                    auto_discovered.add(conn)
         self._log_connection_changes()
         # now that it is logged, add the 'Add another' tuple
         self._connection_tuples += [(_("Add another"), _("Add another"))]

ardupilot_methodic_configurator/backend_flightcontroller_protocols.py

@@ -24,6 +24,7 @@
 SPDX-License-Identifier: GPL-3.0-or-later
 """
 
+from collections.abc import Sequence
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Callable, Optional, Protocol, Union
 
@@ -97,7 +98,7 @@ def baudrate(self) -> int:
     def discover_connections(
         self,
         progress_callback: Optional[Callable[[int, int], None]] = None,
-        preserved_connections: Optional[list[str]] = None,
+        preserved_connections: Optional[Sequence[str]] = None,
     ) -> None: ...
 
     def disconnect(self) -> None: ...

ardupilot_methodic_configurator/frontend_tkinter_connection_selection.py

@@ -122,6 +122,14 @@ def __init__(  # pylint: disable=too-many-arguments, too-many-positional-argumen
         # Start periodic port refresh
         self.start_periodic_refresh()
 
+    def _persist_and_cache_connection(self, connection_string: str) -> None:
+        """Persist a connection string to settings and update the in-memory history cache."""
+        ProgramSettings.store_connection(connection_string)
+        # Update cache in-memory (most-recent-first, deduplicated) to avoid a disk re-read.
+        self._connection_history_cache = [connection_string] + [
+            c for c in self._connection_history_cache if c != connection_string
+        ]
+
     def start_periodic_refresh(self) -> None:
         """Start periodic refresh of available ports every 3 seconds."""
         if self._refresh_timer_id is None:
@@ -212,11 +220,7 @@ def add_connection(self) -> str:
             ),
         )
         if selected_connection:
-            ProgramSettings.store_connection(selected_connection)
-            # Update cache in-memory (most-recent-first, deduplicated) to avoid a disk re-read.
-            self._connection_history_cache = [selected_connection] + [
-                c for c in self._connection_history_cache if c != selected_connection
-            ]
+            self._persist_and_cache_connection(selected_connection)
             error_msg = _("Will add new connection: {selected_connection} if not duplicated")
             logging_debug(error_msg.format(**locals()))
             self.flight_controller.add_connection(selected_connection)
@@ -275,11 +279,7 @@ def reconnect(self, selected_connection: str = "") -> bool:  # Default is auto-c
             self.previous_selection = connection_identifier
             # Persist the connection so it is available next time the program opens
             # and so it survives periodic auto-discovery refreshes during the current session.
-            ProgramSettings.store_connection(connection_identifier)
-            # Update cache in-memory (most-recent-first, deduplicated) to avoid a disk re-read.
-            self._connection_history_cache = [connection_identifier] + [
-                c for c in self._connection_history_cache if c != connection_identifier
-            ]
+            self._persist_and_cache_connection(connection_identifier)
             self.flight_controller.add_connection(connection_identifier)
         if self.destroy_parent_on_connect:
             self.parent.root.destroy()