move zoom_to_rank computation to extra file

nominatim/api/v1/helpers.py

@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2023 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+Helper function for parsing parameters and and outputting data
+specifically for the v1 version of the API.
+"""
+
+REVERSE_MAX_RANKS = [2, 2, 2,   # 0-2   Continent/Sea
+                     4, 4,      # 3-4   Country
+                     8,         # 5     State
+                     10, 10,    # 6-7   Region
+                     12, 12,    # 8-9   County
+                     16, 17,    # 10-11 City
+                     18,        # 12    Town
+                     19,        # 13    Village/Suburb
+                     22,        # 14    Hamlet/Neighbourhood
+                     25,        # 15    Localities
+                     26,        # 16    Major Streets
+                     27,        # 17    Minor Streets
+                     30         # 18    Building
+                    ]
+
+
+def zoom_to_rank(zoom: int) -> int:
+    """ Convert a zoom parameter into a rank according to the v1 API spec.
+    """
+    return REVERSE_MAX_RANKS[max(0, min(18, zoom))]