find the change in a value over time

gistfile1.clj

(defn find-case-insensitive
  [db attr val]
  (let [a (dq/qe-or-nil
           '[:find ?account
             :in $ ?pattern ?attr
             :where
             [?account ?attr ?name]
             [(re-find ?pattern ?name)]]
           db
           (re-pattern (str "(?i)^" val "$")) attr)]
    (when (account? a) a)))

(defn find-by-name
  "Case-insensitive search for account name"
  [db account-name]
  (find-case-insensitive db :account/name (name account-name)))

(defn get-level [db name]
  (-> (find-by-name db name) :account/level))

(defn change-since [past-date db]
  (- (or (get-level db :my-username) 0)
     (or (get-level (d/as-of db past-date) :my-username) 0)))