Convert Heroku DB URL into a JDBC url

heroku_to_jdbc.clj

(ns heroku-to-jdbc
  "untested and brittle parser - use at your own peril")
  
(defn colon?
  [_ c]
  (= c \:))

(defn label-result [result label]
  (update result 0 (fn [x] [label x])))

(defn flip-switch [pred]
  (let [flipped? (atom false)]
    (fn [& args]
      (if-not @flipped?
        (let [result (apply pred args)]
          (if result
            (do
              (reset! flipped? true)
              result)
            result))
        true))))

(defn split [s pred]
  (let [pred* (flip-switch pred)]
    (reduce (fn [[left right] c]
              (if (pred* s c)
                [left (str right c)]
                [(str left c) right]))
            ["" ""]
            s)))

(defn parse-jdbc-url [url]
  (reduce (fn [[bits remaining-url] f]
            (let [result (f remaining-url)]
              [(conj bits (first result)) (second result)]))
          [{} url]
          [(fn hostname [url]
             (label-result (split url colon?) :hostname))
           (fn user [url]
             (label-result (split (drop 3 url) colon?) :user))
           (fn password [url]
             (label-result (split (drop 1 url) (fn [_ c] (= c \@))) :password))
           (fn pg-dns-hostname [url]
             (label-result [(apply str (drop 1 url)) ""] :pg-dns-hostname))]))

(defn recombine-url [bits]
  (let [{:keys [hostname user password pg-dns-hostname]} bits]
    (str "jdbc:" hostname "ql://" pg-dns-hostname "?user=" user "&password=" password)))

(defn heroku->jdbc [url]
  (recombine-url (first (parse-heroku-url url))))

(heroku->jdbc
  "postgres://theuser:[email protected]:5432/pgdbname")

;;=> "jdbc:postgresql://ec1-23-456-789-012.us-west-9001.compute.amazonaws.com:5432/pgdbname?user=theuser&password=pa$$w0rd!"