Undo datomic transaction

rollback.clj

(defn rollback
  "Reassert retracted datoms and retract asserted datoms in a transaction,
  effectively \"undoing\" the transaction.
  
  WARNING: *very* naive function!"
  [conn tx]
  (let [tx-log (-> conn d/log (d/tx-range tx nil) first)
        txid   (-> tx-log :t d/t->tx)
        newdata (->> (:data tx-log)
                     (remove #(= (:e %) txid))
                     (map #(do [(if (:added %) :db/retract :db/add) (:e %) (:a %) (:v %)]))
                     reverse)]
    @(d/transact conn newdata)))