work-once.clj

(ns trillain.handler
  (:require [clojure.string :as string]
            [compojure.core :refer [defroutes GET]]
            [compojure.route :as route]
            [ring.middleware.defaults :refer [site-defaults wrap-defaults]]))

(defonce store (atom {}))
(defonce job-eta-in-sec 10000)

(defn- job []
  (Thread/sleep job-eta-in-sec)
  (rand-int 42))

(defn- result [id]
  (if-let [work (get @store id)]
    (deref work)
    (-> store
        (swap! assoc id (future (job)))
        (get id)
        (deref))))

(defn- call [id]
  {:status 200 :body (str (result id))})

(defroutes app-routes
  (GET "/call" [id] (call id))
  (route/not-found "You have reached basically, nowhere."))

(def app (wrap-defaults app-routes site-defaults))