Replace psycopg2 use with sqlalchemy

Closes: #19

geocode/scotland.py

@@ -1,16 +1,17 @@
 """Reverse geocode civil parishes in Scotland."""
 
-import psycopg2
-from flask import current_app
+from sqlalchemy import func
+
+from geocode.database import session
+from geocode.model import Scotland
 
 
-def get_scotland_code(lat: str | float, lon: str | float) -> str | None:
+def get_scotland_code(lat: float, lon: float) -> str | None:
     """Find civil parish in Scotland for given lat/lon."""
-    conn = psycopg2.connect(**current_app.config["DB_PARAMS"])
-    cur = conn.cursor()
-
-    point = f"ST_Transform(ST_SetSRID(ST_MakePoint({lon}, {lat}), 4326), 27700)"
-    cur.execute(f"select code, name from scotland where st_contains(geom, {point});")
-    row = cur.fetchone()
-    conn.close()
-    return row[0] if row else None
+    point = func.ST_Transform(func.ST_SetSRID(func.ST_MakePoint(lon, lat), 4326), 27700)
+    result = (
+        session.query(Scotland.code)
+        .filter(func.ST_Contains(Scotland.geom, point))
+        .first()
+    )
+    return result[0] if result else None