gistfile1.txt

(defmulti watch-changes
  "Provided a database (database meta, java.net.URL, or database name) and a callback, watches
   for changes to the database and executes the given callback (takes one argument) on every change
   to a document in the given database, using the meta of the changed document as the only
   argument of the callback."
  database-arg-type)

(defn- watch-changes-handler
  [url-str agnt]
  (if (h/success? agnt)
    (loop [lines (io/read-lines (h/stream agnt))]
      (if-let [watched-db (@watched-databases url-str)]
        (when (not (empty? lines))
          (future
            (let [line (first lines)]
              (try
               ((:callback watched-db) (binding [json-read/*json-keyword-keys* true]
                                         (json-read/read-json line)))
               (catch Exception e
                 (dosync
                  (if (@watched-databases url-str)
                    (alter watched-databases update-in [url-str :last-error]
                           (constantly {:execption e :time (java.util.Date.) :data line}))))))))
          (recur (rest lines)))))))

(defmethod watch-changes :name
  [db-name callback & options]
  (apply watch-changes (assoc @*defaults* :name db-name) callback options))

(defmethod watch-changes :url
  [url callback & options]
  (apply watch-changes (utils/url->db-meta url) callback options))

(defmethod watch-changes :meta
  [db-meta callback & options]
  (let [url-str     (utils/db-meta->url db-meta)
        options-map (merge (first options) {:heartbeat 30 :feed "continuous"})]
    (dosync
     (if (contains? @watched-databases url-str)
       (alter watched-databases update-in [url-str :callback] (constantly callback))
       (alter watched-databases assoc url-str
              {:http-agent (h/http-agent
                            (str url-str "/_changes" (utils/map-to-query-str options-map false))
                            :method "GET"
                            :handler (partial watch-changes-handler url-str))
               :callback    callback})))
       db-meta))