Vector items diff and apply.

diff_and_apply.clj

(require '[clojure.set :refer [difference intersection]])

(defn diff [x y k]
  (let [xks (set (map k x))
        yks (set (map k y))
        y-map (zipmap (map k y) y)
        x-map (zipmap (map k x) x)
        cancel (difference xks yks)
        commit-ks (difference yks xks)
        commit (vec (vals (select-keys y-map commit-ks)))
        transact-ks (filter #(not= (x-map %) (y-map %))
                            (intersection xks yks))
        transact (select-keys y-map transact-ks)]
    {:key k
     :commit commit
     :transact transact
     :cancel cancel}))

(defn apply-diff [x d]
  (let [{:keys [commit transact cancel key]} d
        committed (concat x commit)
        mapped (zipmap (map key committed) committed)
        cancelled (apply dissoc mapped cancel)
        transacted (merge cancelled transact)]
    (vec (vals transacted))))

(comment
  TEST BEGIN

  (diff [{:db/id 1 :name "foo"}
         {:db/id 2 :name "bar"}
         {:db/id 3 :name "baz"}]

        [{:db/id 1 :name "foo"}
         {:db/id 2 :name "cat"}
         {:db/id 4 :name "dog"}]

        :db/id)
  ;; =>
  ;; {:key :db/id
  ;;  :commit [{:db/id 4 ,:name "dog"}]
  ;;  :transact {2 {:db/id 2 ,:name "cat"}}
  ;;  :cancel #{3}}

  (apply-diff [{:db/id 1 :name "foo"}
               {:db/id 2 :name "bar"}
               {:db/id 3 :name "baz"}]

              {:key :db/id
               :commit [{:db/id 4 ,:name "dog"}]
               :transact {2 {:db/id 2 ,:name "cat"}}
               :cancel #{3}})
  ;; =>
  ;; [{:db/id 1 :name "foo"}
  ;;  {:db/id 2 :name "bar"}
  ;;  {:db/id 3 :name "baz"}]

  TEST END)