playing-with-projections try with Clojure

playing-with-projections.clj

(ns playing-with-projections.core
  (:require [clojure.data.json :as json]))

;; time helpers with Java 8 API
(def zoneId (java.time.ZoneId/systemDefault))
(defn parse-timestamp [str] (java.time.Instant/parse str))
(defn convert-to-datetime [instant] (java.time.LocalDateTime/ofInstant instant zoneId))

(defn enrich-datetime-info [event]
  (let [instant (parse-timestamp (get event "timestamp"))
        datetime (convert-to-datetime instant)]   
        (assoc event
          "instant" instant
          "datetime" datetime)))
  
;;loading json content
(defn parse-events-file [path]
  (->> (slurp path)
    (json/read-str)
    (map enrich-datetime-info)))

;; projections

(defn count-events [events] (count events))

(defn group-by-type [events] (group-by #(get % "type") events))

(defn extract-year-month [event] 
  (let [datetime (get event "datetime")]
        (.format (java.time.format.DateTimeFormatter/ofPattern "yyyy-MM") datetime)))

(defn fmap [])

(defn count-registration-by-month [registrations]
  (let [by-month (group-by #(extract-year-month %) registrations)]
    (map (fn [[k v]] [k (count v)]) by-month)))

(defn group-events-by [events & args]
  (group-by #(get-in % args) events))

(defn retrieve-title [quizes id] 
  (let [quiz (first (filter #(= (get % "quiz_id") id) quizes))]()
        (get quiz "quiz_title")))

(defn most-popular-quizzes [grouped-by-type] 
  (let [quizes (map #(get % "payload") (get grouped-by-type "QuizWasCreated"))]
        (->> (get grouped-by-type "GameWasOpened")
              (map #(get % "payload"))
              (group-by #(get % "quiz_id"))
              (map (fn [[k v]] [k (count v)]))
              (map #(conj % (retrieve-title quizes (first %))))
              (sort-by #(nth % 1))
              (reverse)
              (map #(str "quiz_id:" (nth % 0) " , quiz_title:" (nth % 2) " , games_played:" (nth % 1))))))

(defn -main [& args]
  (let [events (parse-events-file (first args))
        grouped-by-type (group-by-type events)]
        (println "Count player registration" (count (get grouped-by-type "PlayerHasRegistered"))
        (println "Count player registration by month" (count-registration-by-month (get grouped-by-type "PlayerHasRegistered"))))
        (println "5 Most popular quizzes" (map println (take 5 (most-popular-quizzes grouped-by-type))))
      ))