entity_patch.clj

(ns cpdx.db.entity-patch
  (:require [clojure.data :as data]
            [slingshot.slingshot :refer [throw+]]))

(defn pair->assertion [verb id-ref [attr value]]
  [verb id-ref attr value])

(defn make-assertions [verb id-ref pairs]
  (map (partial pair->assertion verb id-ref)
       pairs))

(defn resolve-patch [id-attr previous current]
  (let [[removed added retained] (data/diff previous current)
        id-ref [id-attr (current id-attr)]]
    (when-not (contains? retained id-attr)
      (throw+ :ids-disagree))
    (into []
          (comp cat (remove nil?))
          [(make-assertions :db/retract id-ref removed)
           (make-assertions :db/add id-ref added)])))