Dynamic Cursor for Reagent

dynamic-cursor

(ns main.hello
  (:require
    [clojure.walk :as walk]
    [reagent.core :as r]))



(enable-console-print!)

;  Advantages of Dynamic Cursor vs Reagent's own Cursor-as-function:
;
;  1. Does not expose the bare-bone atom interface. So swap!, reset! assoc, assoc-in and @ are replaced by simple cGet/cSet methods
;
;  2. All cursors are created dynamically during the get operation and extend their root path with the sub-path you provide in 
;  the get operation such that updating the cursor of a deeply nested child won't cause Reagent to update (via React) components 
;  whose state dependencies are higher up in the path. This optimization typically involves
;  having to manually define cursors of cursors and then use them in updating and dereferencing. This takes care of it dynamically
;  at run time.
;
;  3. You can define in-transform and out-transform as part of each cursor and you can decide when to enable the transform
;
;  4. You can define multiple cursors in on cursor instance so you can pass a whole bunch of related cursors with one map
;

(defn fmap [f m]
  (into (empty m) (for [[k v] m] [k (f v)])))

; example state ratom
(def state-atom (r/atom {:parentA {
                                  :child {:test1 8}
                                  }
                       :parentB {
                                  :child 111
                                  }

                       :parentC {
                                  :child 211
                                  }
                       }))
; transforms
;
(defn double-it-map [m]
  (fmap #(* % 2) m))

(defn keywordize [string-map]
                    (walk/keywordize-keys string-map))

;------------------------------------------------------------------------------------------
; Dynamic Cursor v0.1
;

; Interface
(defprotocol DynamicCursorInterface
  (cGet [this c] [this c p])
  (cSet [this c v] [this c p v]))

; Class
(defrecord DynamicCursor [cursors]
  DynamicCursorInterface
  ;; get
  (cGet [this c]
    (let [out-transform (or (:out-transform (c cursors)) identity)]
    (if (keyword? c)
      (let [cursor (r/cursor state-atom (:path (c cursors)))]
        ; apply out-transform
        (try
          (out-transform @cursor)
          (catch js/Object e
            (println (.-stack e))
            ))
        )
      (throw (.-stack (js/Error.
                        "invalid type: expected :cursor-id"))))))
  (cGet [this c p]
    (let [out-transform (or (:out-transform (c cursors)) identity)]
    (if (and (keyword? c) (vector? p))
      (let [cursor (r/cursor state-atom (into (:path (c cursors)) p))]
        ; don't apply out-transform on nested path
        @cursor)
      (throw
              (.-stack (js/Error.
                         "invalid types: expected :cursor-id and [:sub-path]"))))))
  ;; set
  (cSet [this c v]
    (let [in-transform (or (:in-transform (c cursors)) identity)]
    (if (keyword? c)
      ; apply in-transform
      (try
      (swap! state-atom assoc-in (:path (c cursors)) (in-transform v))
        (catch js/Object e
          (println (.-stack e))))
      (throw
        (.-stack (js/Error.
                   "invalid types: expected :cursor-id and value"))))))
  (cSet [this c p v]
    (let [in-transform (or (:in-transform (c cursors)) identity)]
    (if (and (keyword? c) (vector? p))
      ; don't apply in-transform on nested path
      (swap! state-atom assoc-in (into (:path (c cursors)) p) v)
      (throw
              (.-stack (js/Error.
                         "invalid types: expected :cursor-id [:sub-path] and value")))))))

; Instance
(def abc-cursor (DynamicCursor. {
                         :my-test-cursor-1 {
                                             :path [:parentA :child]
                                             :in-transform keywordize
                                             :out-transform double-it-map
                                             }
                         :my-test-cursor-2 {
                                             :path [:parentB :child]
                                             :in-transform nil
                                             :out-transform nil
                                             }
                        }
           ))

(println "Get value at my-test-cursor-2 where out-transform = nil: "
  (cGet abc-cursor :my-test-cursor-2))

(println "Get value at my-test-cursor-1 where out-transform = double-it-map: "
  (cGet abc-cursor :my-test-cursor-1))

(println "Set value at my-test-cursor-1 to string map {\"test\" 10} where in-transform = keywordize: "
  (cSet abc-cursor :my-test-cursor-1 {"test" 10}))

; Console Output
;
;Get value at my-test-cursor-2 where out-transform = nil:  111
;core.cljs:116Get value at my-test-cursor-1 where out-transform = double-it-map:  {:test1 16}
;core.cljs:116Set value at my-test-cursor-1 to string map {"test" 10} where in-transform = keywordize:  {:parentA {:child {:test 10}}, :parentB {:child 111}, :parentC {:child 211}}