fix(grfn/bbbg): Properly handle already-existing user

If a user already exists with the discord ID we just authenticated, just
return it rather than trying to create another user.

Change-Id: I582c4c8c55f6fb399295b3e691b0bc59e77151f4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4410
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

users/grfn/bbbg/src/bbbg/db/user.clj

@@ -8,3 +8,12 @@
               (select-keys attrs [::user/id
                                   ::user/username
                                   ::user/discord-user-id])))
+
+(defn find-or-create! [db attrs]
+  (or
+   (db/fetch db {:select [:*]
+                 :from [:public.user]
+                 :where [:=
+                         :discord-user-id
+                         (::user/discord-user-id attrs)]})
+   (create! db attrs)))

users/grfn/bbbg/src/bbbg/handlers/home.clj

@@ -35,7 +35,7 @@
      (let [token (get-in request [:oauth2/access-tokens :discord])]
        (if (discord.auth/check-discord-auth env token)
          (let [discord-user (discord/me token)
-               user (db.user/create!
+               user (db.user/find-or-create!
                      db
                      #::user{:username (:username discord-user)
                              :discord-user-id (:id discord-user)})]