Add guessing of country for named places #121

geocoder/namedplace/namedplace_country_guessing.sql

@@ -0,0 +1,35 @@
+-- Return a guess about the country where the places are located, if possible.
+-- E.g: SELECT namedplace_guess_country(Array['granada', 'jaen', 'cordoba', 'madrid', 'valladolid']); => NULL
+-- E.g: SELECT namedplace_guess_country(Array['granada', 'jaén', 'córdoba', 'madrid', 'valladolid', 'peligros'])); => 'ES'
+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;