Update DESIGN.md

DESIGN.md

@@ -21,17 +21,21 @@ sequenceDiagram
     Google Calendar->>CalDAV (F1): GET
     CalDAV (F1)->>Memcached: GET (SUPERSTAR PLAYER)
     Memcached-->>CalDAV (F1): MISS
+    CalDAV (F1)->>Memcached: IS VALID GAME
+    Memcached-->>CalDAV (F1): YES
     CalDAV (F1)->>Memcached: GET (GAME)
     Memcached-->>CalDAV (F1): MISS
     CalDAV (F1)->>Liquipedia.net: GET
     Liquipedia.net-->>CalDAV (F1): RESPONSE
     CalDAV (F1)->>Memcached: CREATE (GAME HTML)
     CalDAV (F1)-->>CalDAV (F1): PARSE HTML, FILTER PLAYERS
     CalDAV (F1)-->>CalDAV (F1): CREATE CALENDAR
-    CalDAV (F1)-->>Memcached: CREATE (SUPERSTAR PLAYER)
+    CalDAV (F1)->>Memcached: CREATE (SUPERSTAR PLAYER)
     CalDAV (F1)-->>Google Calendar: CALENDAR
 ```
 
+Note that `IS VALID GAME` will be a check on validity of the request. Assuming it is a well intentioned user, it will always be yes, and very oftenly a cache hit.
+
 ### Cache hit (game)
 
 Once a first request has been made, the data will be stored in the cache. Subsequent requests will be served from the cache, which is much faster than fetching the data from Liquipedia.net.
@@ -50,6 +54,8 @@ sequenceDiagram
     Google Calendar->>CalDAV (F1): GET
     CalDAV (F1)->>Memcached: GET (SUPERSTAR PLAYER)
     Memcached-->>CalDAV (F1): MISS
+    CalDAV (F1)->>Memcached: IS VALID GAME
+    Memcached-->>CalDAV (F1): YES
     CalDAV (F1)->>Memcached: GET (GAME)
     Memcached-->>CalDAV (F1): RESPONSE (HTML)
     CalDAV (F1)-->>CalDAV (F1): PARSE HTML, FILTER PLAYERS
@@ -75,3 +81,47 @@ sequenceDiagram
     Memcached-->>CalDAV (F1): RESPONSE (CALENDAR)
     CalDAV (F1)-->>Google Calendar: CALENDAR
 ```
+
+### Protecting against non valid use
+
+If a mal intentioned user use a non valid game entry, it should in theory not proceed to an HTTP request to liquipedia.net, and deny instantly.
+To do so, here's the `IS VALID GAME` check detailed :
+
+**Valid games entry empty, invalid game**
+
+```mermaid
+sequenceDiagram
+    participant Google Calendar
+    box GCP App Engine
+        participant CalDAV (F1)
+        participant Memcached
+    end
+    participant Liquipedia.net
+    Google Calendar->>CalDAV (F1): GET
+    CalDAV (F1)->>Memcached: GET (SUPERSTAR PLAYER)
+    Memcached-->>CalDAV (F1): MISS (if HITS, the check is skipped)
+    CalDAV (F1)->>Memcached: GET VALID GAMES
+    Memcached-->>CalDAV (F1): MISS
+    CalDAV (F1)->>Liquipedia.net: GET VALID GAMES
+    Liquipedia.net -->> CalDAV (F1): JSON RESPONSE
+    CalDAV (F1)->>Memcached: SET VALID GAMES FOR UNDETERMINED LIFETIME
+    CalDAV (F1)-->>Google Calendar: 400 Bad Request
+```
+
+**Valid games entry filled, invalid game**
+
+```mermaid
+sequenceDiagram
+    participant Google Calendar
+    box GCP App Engine
+        participant CalDAV (F1)
+        participant Memcached
+    end
+    participant Liquipedia.net
+    Google Calendar->>CalDAV (F1): GET
+    CalDAV (F1)->>Memcached: GET (SUPERSTAR PLAYER)
+    Memcached-->>CalDAV (F1): MISS (if HITS, the check is skipped)
+    CalDAV (F1)->>Memcached: GET VALID GAMES
+    Memcached-->>CalDAV (F1): HIT
+    CalDAV (F1)-->>Google Calendar: 400 Bad Request
+```