add framework for analysing housenumbers

This lays the groundwork for adding variants for housenumbers.
When analysis is enabled, then the 'word' field in the word table
is used as usual, so that variants can be created. There will be
only one analyser allowed which must have the fixed name
'@housenumber'.

nominatim/tokenizer/icu_tokenizer.py

@@ -485,18 +485,36 @@ class LegacyICUNameAnalyzer(AbstractAnalyzer):
         """ Normalize the housenumber and return the word token and the
             canonical form.
         """
-        norm_name = self._search_normalized(hnr.name)
-        if not norm_name:
-            return None, None
+        analyzer = self.token_analysis.analysis.get('@housenumber')
+        result = None, None
 
-        token = self._cache.housenumbers.get(norm_name)
-        if token is None:
-            with self.conn.cursor() as cur:
-                cur.execute("SELECT getorcreate_hnr_id(%s)", (norm_name, ))
-                token = cur.fetchone()[0]
-                self._cache.housenumbers[norm_name] = token
+        if analyzer is None:
+            # When no custom analyzer is set, simply normalize and transliterate
+            norm_name = self._search_normalized(hnr.name)
+            if norm_name:
+                result = self._cache.housenumbers.get(norm_name, result)
+                if result[0] is None:
+                    with self.conn.cursor() as cur:
+                        cur.execute("SELECT getorcreate_hnr_id(%s)", (norm_name, ))
+                        result = cur.fetchone()[0], norm_name
+                        self._cache.housenumbers[norm_name] = result
+        else:
+            # Otherwise use the analyzer to determine the canonical name.
+            # Per convention we use the first variant as the 'lookup name', the
+            # name that gets saved in the housenumber field of the place.
+            norm_name = analyzer.normalize(hnr.name)
+            if norm_name:
+                result = self._cache.housenumbers.get(norm_name, result)
+                if result[0] is None:
+                    variants = analyzer.get_variants_ascii(norm_name)
+                    if variants:
+                        with self.conn.cursor() as cur:
+                            cur.execute("SELECT create_analyzed_hnr_id(%s, %s)",
+                                        (norm_name, list(variants)))
+                            result = cur.fetchone()[0], variants[0]
+                            self._cache.housenumbers[norm_name] = result
 
-        return token, norm_name
+        return result
 
 
     def _compute_partial_tokens(self, name):