Add guessing function and tests to extension

geocoder/extension/sql/0.0.1/40_namedplaces.sql

@@ -288,6 +288,40 @@ CREATE OR REPLACE FUNCTION geocode_namedplace(places text[]) RETURNS SETOF geoco
 END
 $$;
 
+CREATE OR REPLACE FUNCTION namedplace_guess_country(places text[])
+RETURNS text AS $$
+DECLARE
+  country_code text;
+  threshold CONSTANT float := 0.8;
+  input_length integer := array_length(places, 1);
+BEGIN
+  BEGIN
+    WITH hist AS (
+        SELECT count(DISTINCT(lower(p.s), gp.iso2)) AS c, iso2
+        FROM global_cities_points_limited gp
+        inner join (SELECT unnest(places) AS s) p
+        ON (gp.lowername = lower(s))
+        GROUP BY iso2
+      ),
+      best_two AS (
+        SELECT iso2, c
+          FROM hist
+          WHERE c > input_length * threshold
+          ORDER BY c DESC
+          LIMIT 2
+      )
+    SELECT iso2 INTO STRICT country_code
+      FROM (SELECT iso2, c, max(c) over() AS maxcount FROM best_two) bt
+      WHERE bt.c = bt.maxcount;
+    EXCEPTION
+      WHEN NO_DATA_FOUND OR too_many_rows THEN
+        RETURN NULL;
+  END;
+  RETURN country_code;
+END;
+$$ LANGUAGE 'plpgsql' SECURITY DEFINER IMMUTABLE;
+
+
 --------------------------------------------------------------------------------
 
 -- Support tables