[hw-3] loms service

docs/homework-3/img/cart-cart-checkout.plantuml

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+@startuml
+
+actor User as u
+collections Cart as c
+database CartStorage as cs
+collections Order as o
+
+u -> c : POST /checkout/<user_id>
+activate c
+c -> cs : cart.GetItemsByUserID
+c -> o : gRPC Loms.OrderCreate\n\t- user\n\t- []item
+c -> cs : cart.DeleteItemsByUserID
+
+c -> u : Response: 200 OK
+
+deactivate c
+
+@enduml