defmodule Fly do
  @otp_app :fly
  @moduledoc """
  Fly is an OTP application you can use to transform files on the fly with various workers.
  """
  use Application
  require Logger

  # 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

    # Define workers and child supervisors to be supervised
    children = [
      # Starts a worker by calling: Fly.Worker.start_link(arg1, arg2, arg3)
      # worker(Fly.Worker, [arg1, arg2, arg3]),
    ]

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

  @doc """
  Run the worker specified by the `config_atom`, passing it the `input`, and
  merging the `options` into the configuration for the specified worker at
  runtime.
  """
  @spec run(atom(), binary(), map()) :: binary()
  def run(config_atom, input, options \\ %{})
          when is_atom(config_atom)
          and is_binary(input)
          and is_map(options) do
    case get_module_and_configuration(config_atom) do
      {mod, config} ->
        apply(mod, :call, [input, Map.merge(config, options)])
      _ ->
        Logger.error """
        No such Fly configuration: #{config_atom}.  Have you configured it?  It should
        look like:

            config :fly, :workers,
              %{
                #{config_atom}: {Fly.Worker.SomeModule, %{some: :config}}
              }

        You can look up the configuration options for the module you're trying to use in
        its documentation.
        """
    end
  end

  @spec get_module_and_configuration(atom()) :: {atom(), map()}
  defp get_module_and_configuration(config_atom) do
    @otp_app
      |> Application.get_env(:workers)
      |> Map.get(config_atom)
  end
end