http_poll.core.cljs

(ns http-poll.core
  (:require [clojure.core.async
             :refer [>! <! go chan timeout]]
            [clj-http.client :as http]))

(defn print-status
  [uid s]
  (println (str (subs (str uid) 0 4) " " s)))

(defn init-request
  [url uid]
  (print-status uid "Started request")
  (let [start-chan (chan)]
    (go
      ;; Simulating 1 sec to init http request
      (<! (timeout 1000))
      ;; Simulating start or fail,
      ;; will be replaced by actual http request
      (>! start-chan (rand-nth [:started :started :started :failed])))
    start-chan))

(defn poll
  [url uid]
  (print-status uid "Polling")
  (let [poll-chan (chan)]
    (go
      ;; Simulating 1 sec for http request.
      ;;
      (<! (timeout 1000))
      ;; Simulating status of poll,
      ;; will be replace by actual http request
      (>! poll-chan (rand-nth [:ongoing :ongoing :ongoing :completed :failed])))
    poll-chan))

(def statuses (atom {}))

(defn set-status!
  [uid status]
  (print-status uid (str "status of uid =" status))
  (swap! statuses #(assoc % uid status)))

(defn start-poll
  []
  (let [uid (java.util.UUID/randomUUID)
        url (str "some-url?uid=" uid)]
    (set-status! uid :initializing)
    (go (let [start-chan (init-request url uid)
              status (<! start-chan)]
          (print-status uid "Init request finished")
          (set-status! uid status)
          (when-not (= :failed (get @statuses uid))
            (print-status uid "Polling started")
            (while (contains? #{:started :ongoing} (get @statuses uid))
              ;; Poll once every second
              (<! (timeout 1000))
              (let [poll-chan (poll url uid)]
                (set-status! uid (<! poll-chan))))))
        (print-status uid (str "Request completed with status " (get @statuses uid))))
    uid))

;(start-poll) ;; Returns uid immediately
;d82e status of uid =:initializing
;d82e Started request
;=> #uuid"d82e9750-ce32-4d1f-b30d-b866b3c73903" 
;d82e Init request finished
;d82e status of uid =:started
;d82e Polling started
;d82e Polling
;d82e status of uid =:failed
;d82e Request completed with status :failed

 ;; Starts 10 simultaneous polls. About 4 seem to run concurrently. 
 ;; It's possible to interact with the REPL during the run
;(repeatedly 10 start-poll)
;7bec status of uid =:initializing
;4eaf status of uid =:initializing
;7bec Started request
;4eaf Started request
;9d35 status of uid =:initializing
;9d35 Started request
;76cd status of uid =:initializing
;4393 status of uid =:initializing
;6cb3 status of uid =:initializing
;b38e status of uid =:initializing
;7ebb status of uid =:initializing
;13e0 status of uid =:initializing
;776c status of uid =:initializing
;=>
;(#uuid"7bec8224-aef9-4cb9-b979-de101f952a0b"
;  #uuid"4eafa5db-52f4-409e-8f7e-dbc383afd601"
;  #uuid"9d35169f-8930-4be4-bbc1-93b1b7f30d4b"
;  #uuid"76cd484b-66f8-4798-a0ba-3fc286c2883b"
;  #uuid"4393a084-09cb-4f82-bb78-0e4a58d19543"
;  #uuid"6cb3158a-7102-4531-a10f-bc1fadc3f1c0"
;  #uuid"b38e984f-e21b-4eb3-ae7c-0642ae04aeb4"
;  #uuid"7ebb9411-a571-4b8f-8955-2cd272ef58e6"
;  #uuid"13e00d6e-2f13-4148-a787-abcc20fe0fa1"
;  #uuid"776c665b-2453-40e3-bec9-1e4da820f87d")
;6cb3 Started request
;b38e Started request
;7ebb Started request
;13e0 Started request
;776c Started request
;76cd Started request
;4393 Started request
;7bec Init request finished
;4eaf Init request finished
;7bec status of uid =:failed
;7bec Request completed with status :failed
;9d35 Init request finished
;4eaf status of uid =:started
;4eaf Polling started
;9d35 status of uid =:started
;9d35 Polling started
;7ebb Init request finished
;13e0 Init request finished
;7ebb status of uid =:failed
;6cb3 Init request finished
;13e0 status of uid =:started
;6cb3 status of uid =:failed
;6cb3 Request completed with status :failed
;b38e Init request finished
;b38e status of uid =:started
;b38e Polling started
;13e0 Polling started
;7ebb Request completed with status :failed
;776c Init request finished
;776c status of uid =:failed
;776c Request completed with status :failed
;76cd Init request finished
;76cd status of uid =:started
;76cd Polling started
;4393 Init request finished
;4393 status of uid =:started
;4393 Polling started
;4eaf Polling
;9d35 Polling
;b38e Polling
;13e0 Polling
;4393 Polling
;76cd Polling
;4eaf status of uid =:completed
;9d35 status of uid =:completed
;9d35 Request completed with status :completed
;4eaf Request completed with status :completed
;13e0 status of uid =:ongoing
;4393 status of uid =:complete
;db38e status of uid =:ongoing
;76cd status of uid =:failed
;76cd Request completed with status :failed
;4393 Request completed with status :completed
;b38e Polling13e0 Polling
;b38e status of uid =:completed
;13e0 status of uid =:ongoing
;b38e Request completed with status :completed
;13e0 Polling
;13e0 status of uid =:ongoing
;13e0 Polling
;13e0 status of uid =:failed
;13e0 Request completed with status :failed