simple-pull-pattern.clj

(declare pull)

(defn- pull-map
  [patterns from]
  (reduce-kv
    (fn [out key sub-pat]
      (assert (vector? sub-pat) "map value must be vector")
      (let [sub (get from key)]
        ;; sub is now either a set or another entity
        (some->>
          (not-empty
            (if ((some-fn set? vector? seq?) sub)
              (mapv #(pull sub-pat %) sub)
              (pull sub-pat sub)))
          (assoc out key))))
    {}
    patterns))

(defn pull
  "Pulls given an entity."
  [patterns ent]
  (reduce
    (fn [out sub-pat]
      (if (map? sub-pat)
        (merge out (pull-map sub-pat ent))
        (if-some [v (get ent sub-pat)]
          (assoc out sub-pat v)
          out)))
    {}
    patterns))