memdb.clj

(ns avalon.models.memdb
  (:use avalon.models.crud))

(defn- char-range [c n]
  (let [idx (int c)]
    (map char (range idx (+ idx n)))))

(def alphabet
  (vec (->> (char-range \a 26)
            (remove #{\a \e \i \o \u}))))

(defn- id-gen []
  (apply str (take 4 (shuffle alphabet))))

(defn create-db []
  (let [db (ref {})]
    (reify CRUD
      (create! [_ entity]
        ; Careful here, this takes the first available id of a lazy infinite sequence
        (let [id (first (drop-while #(contains? @db %) (repeatedly id-gen)))
              entity (assoc entity :id id)]
          (dosync (alter db assoc id entity))
          entity))
      (all [_]
        (vals @db))
      (get [_ id]
        (@db id))
      (exists? [_ id]
        (contains? @db id))
      (update! [_ id f]
        (dosync (alter db update id f)))
      (save! [_ id updates]
        (dosync (alter db update-in [id] merge updates)))
      (relate! [_ id k v]
        (dosync (alter db update-in [id k] conj v)))
      (delete! [_ id]
        (dosync (alter db dissoc id))))))