defmodule Quantum do

  use GenServer

  @typedoc "A cron expression"
  @type expr :: String.t | Atom

  @typedoc "A function/0 to be called when cron expression matches"
  @type fun0 :: (() -> Type)

  @typedoc "A job is defined by a cron expression and a function/0"
  @type job :: {expr, fun0}

  @doc "Adds a new job"
  @spec add_job(expr, fun0) :: :ok
  def add_job(e, fun) do
    GenServer.call(Quantum, {:add, Quantum.Normalizer.normalize({e, fun})})
  end

  @doc "Returns the list of currently defined jobs"
  @spec jobs :: [job]
  def jobs do
    GenServer.call(Quantum, :jobs)
  end

  def init(s) do
    Quantum.Timer.tick
    {:ok, %{s | jobs: run(%{s | r: 1}), r: 0}}
  end

  def handle_call({:add, j}, _, s), do: {:reply, :ok, %{s | jobs: [j | s.jobs]}}
  def handle_call(:jobs, _, s), do: {:reply, s.jobs, s}

  def handle_info(:tick, s) do
    {d, h, m} = Quantum.Timer.tick
    if s.d != d, do: s = %{s | d: d, w: rem(:calendar.day_of_the_week(d), 7)}
    s = %{s | h: h, m: m}
    {:noreply, %{s | jobs: run(s)}}
  end
  def handle_info(_, s), do: {:noreply, s}

  defp run(s) do
    Enum.each s.jobs, &(Task.start Quantum.Executor, :execute, [&1, s])
    s.jobs
  end

end