(.module:
  [library
   [lux "*"
    [abstract
     ["[0]" monad {"+" [do]}]]
    [control
     ["[0]" try {"+" [Try]}]
     [concurrency
      ["[0]" async {"+" [Async]}]]]
    [data
     [collection
      ["[0]" list]
      ["[0]" set]]]
    [world
     [program {"+" [Program]}]
     [shell {"+" [Exit Shell]}]
     [console {"+" [Console]}]
     ["[0]" file
      ["[0]" watch {"+" [Watcher]}]]]]]
  ["[0]" // "_"
   ["/[1]" // "_"
    [command {"+" [Command]}]
    ["[1]" profile]
    ["[1][0]" action]
    [dependency
     [resolution {"+" [Resolution]}]]]])

(def: (targets fs path)
  (-> (file.System Async) file.Path (Async (List file.Path)))
  (let [! async.monad]
    (|> path
        (\ fs sub_directories)
        (\ ! each (|>> (try.else (list))
                       (monad.each ! (targets fs))))
        (\ ! conjoint)
        (\ ! each (|>> list.together (list& path))))))

(def: .public delay
  Nat
  1,000)

(def: (pause delay)
  (-> Nat (Async (Try Any)))
  (async.after delay {try.#Success []}))

(def: .public (do! delay watcher command)
  (All (_ a)
    (-> Nat (Watcher Async)
        (-> (Console Async) (Program Async) (file.System Async) (Shell Async) Resolution (Command [Exit a]))
        (-> (Console Async) (Program Async) (file.System Async) (Shell Async) Resolution (Command [Exit Any]))))
  (function (_ console program fs shell resolution)
    (function (_ profile)
      (with_expansions [<call> ((command console program fs shell resolution) profile)]
        (do [! async.monad]
          [targets (|> profile
                       (value@ ///.#sources)
                       set.list
                       (monad.each ! (..targets fs))
                       (\ ! each list.together))]
          (do [! ///action.monad]
            [_ (monad.each ! (\ watcher start watch.modification) targets)
             _ <call>]
            (loop [_ []]
              (do !
                [_ (..pause delay)
                 events (\ watcher poll [])]
                (case events
                  {.#Item _}
                  (do !
                    [_ <call>]
                    (recur []))

                  {.#End}
                  (recur []))))))))))