port address level computation to Python

Also adds simple tests for correct table creation.

nominatim/tools/refresh.py

@@ -1,6 +1,10 @@
 """
 Functions for bringing auxiliary data in the database up-to-date.
 """
+import json
+
+from psycopg2.extras import execute_values
+
 from ..db.utils import execute_file
 
 def update_postcodes(conn, datadir):
@@ -14,3 +18,54 @@ def recompute_word_counts(conn, datadir):
     """ Compute the frequency of full-word search terms.
     """
     execute_file(conn, datadir / 'sql' / 'words_from_search_name.sql')
+
+
+def _add_address_level_rows_from_entry(rows, entry):
+    """ Converts a single entry from the JSON format for address rank
+        descriptions into a flat format suitable for inserting into a
+        PostgreSQL table and adds these lines to `rows`.
+    """
+    countries = entry.get('countries') or (None, )
+    for key, values in entry['tags'].items():
+        for value, ranks in values.items():
+            if isinstance(ranks, list):
+                rank_search, rank_address = ranks
+            else:
+                rank_search = rank_address = ranks
+            if not value:
+                value = None
+            for country in countries:
+                rows.append((country, key, value, rank_search, rank_address))
+
+def load_address_levels(conn, table, levels):
+    """ Replace the `address_levels` table with the contents of `levels'.
+
+        A new table is created any previously existing table is dropped.
+        The table has the following columns:
+            country, class, type, rank_search, rank_address
+    """
+    rows = []
+    for entry in levels:
+        _add_address_level_rows_from_entry(rows, entry)
+
+    with conn.cursor() as cur:
+        cur.execute('DROP TABLE IF EXISTS {}'.format(table))
+
+        cur.execute("""CREATE TABLE {} (country_code varchar(2),
+                                        class TEXT,
+                                        type TEXT,
+                                        rank_search SMALLINT,
+                                        rank_address SMALLINT)""".format(table))
+
+        execute_values(cur, "INSERT INTO {} VALUES %s".format(table), rows)
+
+        cur.execute('CREATE UNIQUE INDEX ON {} (country_code, class, type)'.format(table))
+
+    conn.commit()
+
+def load_address_levels_from_file(conn, config_file):
+    """ Replace the `address_levels` table with the contents of the config
+        file.
+    """
+    with config_file.open('r') as fdesc:
+        load_address_levels(conn, 'address_levels', json.load(fdesc))