drk-blutspende-orte/docs/architecture.md

Architecture

Everything lives in app.py. There is no package structure.

Components

Class / function	Responsibility
DataStore	Owns orte.csv. Loads it into a pandas DataFrame, exposes read helpers (get_map_data, get_autocomplete_strings, total_count, find_duplicates) and write helpers (append_rows, update_row, delete_rows). All writes go through _save_csv → rotating backup + atomic write. All columns are read as strings. Falls back to an empty frame (or the newest backup) if orte.csv is missing/empty/corrupt.
geocode_city()	Pure function: `(city, plz) -> (lat, lon)
GeocoderWorker	A threading.Thread (daemon). Holds a FIFO list of (row_id, city, plz, callback) items guarded by a lock, woken by an Event. Processes one item per second, calls geocode_city, then invokes callback from the worker thread. Each item is wrapped in try/except so one failure never kills the thread; after SERVICE_ERROR_THRESHOLD consecutive service errors it fires the optional on_service_error callback.
parse_date() / parse_coord() / helpers	Module-level pure functions for normalizing user input (date → ISO, coordinate strings → float, "City (PLZ)" splitting). Shared by the entry tab and EditDialog.
generate_map()	Builds karte.html from DataStore.get_map_data() with Folium.
EditDialog	tk.Toplevel modal dialog for editing one row. Returns its result via self.result.
App	ttkbootstrap.Window. Builds the UI, owns the DataStore, the GeocoderWorker, and the in-memory _queue list for Tab 1.

Data flow

Adding entries

user types -> _on_add_row()
  -> append dict to self._queue
  -> insert row into Tab-1 Treeview (coords = "⏳ wird gesucht…")
  -> geocoder.enqueue(row_id, city, plz, self._geocode_done)

GeocoderWorker thread (1/sec):
  coords = geocode_city(...)
  -> self._geocode_done(row_id, coords)        [worker thread]
       -> self.after(0, self._apply_geocode_result, ...)   [hop to UI thread]
            -> mutate self._queue entry + update Treeview cell

user clicks "Alle speichern" -> _on_save_all()
  -> DataStore.find_duplicates() (status-bar hint only)
  -> DataStore.append_rows()  ->  CSV append + in-memory concat
  -> clear queue, refresh Tab 2, update autocomplete

Editing / deleting

EditDialog -> DataStore.update_row(df_idx, values) or DataStore.delete_rows(indices) -> full df.to_csv() rewrite -> refresh.

Threading model

• Tkinter is single-threaded; all widget access must happen on the main thread.
• The geocoder runs off-thread so the UI never blocks for the 1-second-per-item rate limit.
• The callback is invoked on the worker thread, and every callback in App immediately does self.after(0, ...) to marshal back onto the UI thread. This is the load-bearing convention — any new callback must follow it. (on_service_error does the same.)
• The worker catches every exception per item, so a bug in a callback or a network error logs a traceback but never stops the queue.
• On window close, _on_close() calls geocoder.stop() (sets a flag + wakes the event) and then destroy(). The thread is a daemon, so a missed stop won't hang the process.

Persistence model

• orte.csv is the single source of truth. It is read once at startup and then kept in sync in memory.
• Every write (append, update, delete) rebuilds the full DataFrame and goes through DataStore._save_csv:
  1. _make_backup() – copy the current file to data/backups/orte-YYYYMMDD-HHMMSS.csv (skipped if byte-identical to the newest backup); prune to MAX_BACKUPS (20).
  2. _write_atomic() – write to orte.csv.tmp, fsync, then os.replace() onto orte.csv (atomic on POSIX). A crash mid-write leaves the old file intact.
• A backup is also taken once at startup.
• Still no file locking: if the CSV is edited in another program while the app is open, the next in-app save overwrites those changes (but the pre-write backup captures them).

Logging

_setup_logging() (called from __main__) attaches a RotatingFileHandler to data/app.log (512 KB × 3). Logger name arbeitsorte, module-level log. Records saves, map generation, geocoding failures, and any uncaught exception. This is the file to ask for when diagnosing a problem on the user's laptop.

External dependencies at runtime

Dependency	Needed for	Offline behaviour
Nominatim (OSM)	geocoding new/edited entries	entries save with blank coords, shown as ⚠ nicht gefunden
CDN (jsdelivr, jquery, cloudflare)	rendering karte.html	map page loads blank / unstyled
OpenStreetMap tiles (tile.openstreetmap.org)	map background	blank/grey tiles

Existing entries that already have coordinates do not need the network.