defmodule ChangedReloader do
  use Application

  # See http://elixir-lang.org/docs/stable/elixir/Application.html
  # for more information on OTP Applications
  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    children = [
      # Define workers and child supervisors to be supervised
      worker(ChangedReloader.Worker, [])
    ]

    # See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: Remix.Supervisor]
    Supervisor.start_link(children, opts)
  end

  defmodule Worker do
    use GenServer

    defmodule State, do: defstruct last_mtime: nil

    def start_link do
      Process.send_after(__MODULE__, :poll_and_reload, 10000)
      GenServer.start_link(__MODULE__, %State{}, name: Remix.Worker)
    end

    def handle_info(:poll_and_reload, state) do
      current_mtimes = get_current_mtime
      {latest_mtime, _} = List.first(current_mtimes)

      Enum.filter(current_mtimes, fn  {mtime, _} -> mtime > state.last_mtime end)
      |> Enum.each(fn {_, file} -> IEx.Helpers.c(file) end)

      Process.send_after(__MODULE__, :poll_and_reload, 1000)
      {:noreply, %State{last_mtime: latest_mtime}}
    end

    def get_current_mtime, do: get_current_mtime("lib")

    def get_current_mtime(dir) do
      case File.ls(dir) do
        {:ok, files} -> get_current_mtime(files, [], dir)
        _            -> nil
      end
    end

    def get_current_mtime([], mtimes, _cwd) do
      mtimes
      |> List.flatten
      |> Enum.sort
      |> Enum.reverse
    end

    def get_current_mtime([h | tail], mtimes, cwd) do
      path = "#{cwd}/#{h}"
      mtime = case File.dir?(path) do
        true  -> get_current_mtime(path)
        false ->
          {File.stat!(path).mtime, path}
      end
      get_current_mtime(tail, [mtime | mtimes], cwd)
    end
  end
end