add: img rating fn

main.py

@@ -82,7 +82,21 @@ async def rate_picture(session_id: int, picture_id: int, mark: int):
     )
     sessionid = cur.fetchone()
     if sessionid is None:
-        return  # FIXME[2]  # Q: do we return something specific, or just use convention here?
+        return {
+            "status": "failure"  # FIXME[2]
+        }  # Q: do we return something specific, or just use convention here?
 
     # add new mark to the session table
-    pass
+    try:
+        cur.execute(
+            """INSERT INTO marks(imgid, sessionid, mark)
+                        VALUES(:imgid,:sessionid,:mark)
+                    """,
+            {"imgid": picture_id, "sessionid": sessionid["sessionid"], "mark": mark},
+        )
+    except sqlite3.IntegrityError as e:
+        if str(e) == "UNIQUE constraint failed: marks.imgid, marks.sessionid":
+            return {"status": "already rated"}
+
+    cur.commit()
+    return {"status": "success"}