delayed-chan.clj

(ns delay-chan
  (:require [clojure.core.async :refer [>! <! put! chan timeout go alts!]))

(defonce model-chan (chan))

(defn delay-chan
  "Take a channel to listen to and optional timeout. Returns a sleepy-chan
  Will only publish latest message on sleepy-chan once per timeout."
  [input-chan]
  (let [output-chan (chan)]
    (go
      (loop [timeout-chan (timeout 5000) message nil]
        (let [[value ch] (alts! [timeout-chan input-chan])]
          (if (= input-chan ch)
            (recur timeout-chan value)
            (do
              (when message
                (>! output-chan message))
              (recur (timeout 5000) nil))))))
    output-chan))

(defn listen-to-changes! []
  (let [sleepy-chan (delay-chan model-chan)]
    (go
      (while true
        (try
          (let [latest (<! sleepy-chan)]
           (println "DO DELAYED WORK"))
          (catch Exception e
            (println "Catch in listen-to-changes!" e)))))))

;; Used inside of an add-watch
(defn changed-models [k r a b]
  (when (not= a b)
    (println "changed")
    (put! model-chan :update)))