authorize.clj

(def ^:private last-window-ms 120000)

(def ^:private max-last-txs 3)

defn- authorize-tx [authorizer tx]
  (let [{:keys [active-card available-limit]} authorizer
        {:keys [amount time]} tx]
    (cond
      (nil? active-card)
      (assoc authorizer
        :violations [:account-not-initialized])

      (false? active-card)
      (assoc authorizer
        :violations [:card-not-active])

      (> amount available-limit)
      (assoc authorizer
        :violations [:insufficient-limit])

      :else
      (let [window-start (java.util.Date. (- (.getTime time) last-window-ms))
            authorizer'  (-> authorizer
                           (update :last-txs clear-until window-start))]
        (cond 
          (has-similar? (:last-txs authorizer') tx)
          (assoc authorizer
            :violations [:doubled-transaction])

          (>= (count (:last-txs authorizer')) max-last-txs)
          (assoc authorizer
            :violations [:high-frequency-small-interval])

          :else
          (-> authorizer'
            (update :last-txs conj tx)
            (update :available-limit - (bigint amount))
            (assoc :violations [])))))))

authorize.py

last_window_sec = 120
max_last_txs = 3

fun authorize_tx(authorizer, tx):
  active_card = authorizer.active_card
  available_limit = authorizer.available_limit
  amount = tx.amount
  time = tx.time

  if None == active_card:
    authorizer.violations = ["account-not-initialized"]
    return

  if False == active_card:
    authorizer.violations = ["card-not-active"]
    return

  if amount > available_limit:
    authorizer.violations = ["insufficient-limit"]
    return

  window_start = time.time() - last_window_sec
  clear_until(authorizer, window_start)

  if has_similar(authorizer.last_txs, tx):
    authorizer.violations = ["doubled-transaction"]
    return

  if len(authorizer.last_txs) > max_last_txs:
    authorizer.violations = ["high-frequency-small-interval"]
    return

  authorizer.last_txs.add(tx)
  authorizer.available_limit -= amount
  authorizer.violations = []