es.clj

(def game-results {:rock    {:rock :tie,  :paper :lose, :scissor :win}
                   :paper   {:rock :win,  :paper :tie,  :scissor :lose}
                   :scissor {:rock :lose, :paper :win,  :scissor :tie}})

(defn create-game-command
  [{:keys [aggregate-id player move]} state]
  [{:event        :game-created
    :game-id      aggregate-id
    :creator      player
    :state-change {:state :started :creator player}}
   {:event        :move-decided
    :game-id      aggregate-id
    :player       player
    :move         move
    :state-change {:move move}}])

(defn decide-move-command
  [{:keys [aggregate-id player move]} {creator :creator first-move :move}]
  (let [results-mapping {:win  {:event        :game-won
                                :game-id      aggregate-id
                                :winner       creator
                                :loser        player
                                :state-change {:state :finished}}
                         :lose {:event        :game-won
                                :game-id      aggregate-id
                                :winner       player
                                :loser        creator
                                :state-change {:state :finished}}
                         :tie  {:event        :game-tie
                                :game-id      aggregate-id
                                :state-change {:state :finished}}}
        result (-> game-results first-move move)]
    [{:event        :move-decided
      :game-id      aggregate-id
      :player       player
      :move         move
      :state-change {:move move}}
     (result results-mapping)]))

(defn apply-events [events state]
  (reduce merge state (map :state-change events)))