Add valid lines to stops

app.py

@@ -146,6 +146,43 @@ def register_routes(app):
             ]
         )
 
+    def _line_sort_key(ref):
+        head = ""
+        i = 0
+        while i < len(ref) and not ref[i].isdigit():
+            head += ref[i]
+            i += 1
+        num = ref[i:]
+        digits = ""
+        while num and num[0].isdigit():
+            digits += num[0]
+            num = num[1:]
+        return (head.lower(), int(digits) if digits else -1, num.lower())
+
+    @app.route("/api/lines")
+    @login_required
+    def api_lines():
+        """Line suggestions for the "Linie" field, scoped to the chosen stops."""
+        def stop_lines(param):
+            stop = db.session.get(Stop, int(param)) if (param or "").isdigit() else None
+            return set(stop.line_list()) if stop else set()
+
+        origin = stop_lines(request.args.get("origin_stop_id"))
+        destination = stop_lines(request.args.get("destination_stop_id"))
+        candidates = origin | destination
+        if not candidates:
+            return jsonify([])
+
+        needle = request.args.get("q", "").strip().lower()
+        both = origin & destination
+        refs = sorted(
+            (r for r in candidates if not needle or r.lower().startswith(needle)),
+            key=lambda r: (r not in both, _line_sort_key(r)),
+        )
+        return jsonify(
+            [{"ref": r, "both": r in both} for r in refs[:20]]
+        )
+
     def parse_trip_date(raw_value):
         raw_value = (raw_value or "").strip()
         try: