(defn is-note-off
  "Adds note if was turned off to accumulator"
  [acc [note command]]
  (if (= :note-off command)
    (conj acc note)
    acc))

(defn is-note-on
  "Adds note if was turned on to accumulator"
  [acc [note command]]
  (if (= :note-on command)
    (conj acc note)
    acc))

(defn note-offs
  "Associates a tick with notes turned off at it"
  [acc tick note-events]
  (assoc acc tick (reduce is-note-off [] note-events)))

(defn note-ons
  "Associates a tick with notes turned on at it"
  [acc tick note-events]
  (assoc acc tick (reduce is-note-on [] note-events)))

(defn get-notes-by-type
  "Returns a map: key is tick, value is notes that match the command arg"
  [notes-by-ticks-map command-type]
  (if (= :note-on command-type)
    (reduce-kv note-ons {} notes-by-ticks-map)
    (reduce-kv note-offs {} notes-by-ticks-map)))