tamnoon

defmodule Tamnoon.MethodManager do
  @moduledoc """

  This module handles the management of different methods as you create them.

  Notably, it provides the `defmethod/2` macro.

  > #### Importing the module {: .info}

  > In order to create handlers for the methods you set up, you must `import Tamnoon.MethodManager`

  > in your _methods module_. Then, you can use the `defmethod/2` macro to implement handling

  > of the methods.

  """
  require Logger

  @doc """

  Defines a function named `tmnn_[name]`. Functions with this prefix in your _methods module_

  will automatically be added to the possible methods when invoking `route_request/3`.

  Inside the created function, you can access the state of the client and the request

  object by the `state` and `req` variables respectively.

  Method handlers must return a tuple of `{return_value, new_state}` (note: use `diff/2` for a shorter version).

  ## Example

  ```

  defmethod :get do

    key = get_key(req, state)

    if (key != nil) do

      {state[key], state}

    else

      {"Error: no matching key", state}

    end

  end

  ```

  """
  defmacro defmethod(name, do: block) do
    method_name = String.to_atom("tmnn_" <> Atom.to_string(name))

    quote do
      def unquote(method_name)(req, state) do
        var!(req) = req
        # Use the `req` variable to stop unused variable warnings.

        _ = var!(req)

        var!(state) = state
        unquote(block)
      end
    end
  end

  @doc """

  The function used by `Tamnoon.SocketHandler.websocket_handle/2` to route the requests

  to the appropriate method handler.

  """
  @spec route_request(list(module()), map(), map()) ::

          {:reply, {:text, return_value :: String.t()}, new_state :: map()}
  def route_request(methods_modules, payload, state) do
    method = payload["method"]

    found_func_info =
      Enum.find_value(methods_modules, fn methods_module ->
        func_info =
          methods_module.__info__(:functions)
          |> Enum.find(fn {name, arity} ->
            arity == 2 && Atom.to_string(name) == "tmnn_" <> method
          end)

        if func_info, do: {methods_module, func_info}, else: nil
      end)

    if found_func_info == nil do
      Logger.error("Method '#{method}' not found in any methods module.")

      {:reply, {:text, elem(Jason.encode(%{error: "Method '#{method}' not found."}, []), 1)}, state}
    else
      {methods_module, {func, _arity}} = found_func_info

      {{ret_val, new_state}, []} =
        quote do
          unquote(methods_module).unquote(func)(
            unquote(Macro.escape(payload)),
            unquote(Macro.escape(state))
          )
        end
        |> Code.eval_quoted()

      {:reply, {:text, elem(Jason.encode(ret_val, []), 1)}, new_state}
    end
  end

  @doc """

  Returns a tuple containing the diffs and the new state after applying the diffs.

  Can be used in method handlers to update a value easily.

  ## Example

  ```

  defmethod :change_something do

    diffs = %{some_key: "New value", another_key: "Another value"}



    diff(diffs, state)

  end

  ```

  """
  @spec diff(map(), map()) :: {map(), map()}
  def diff(diffs, state) do
    {diffs, Map.merge(state, diffs, fn _key, _old, new -> new end)}
  end

  @doc """

  Triggers a method with the given name and payload. An additional timeout can be specified

  to delay the triggering of the method.

  """
  @spec trigger_method(atom(), map(), non_neg_integer()) ::

          :ok | :noconnect | :nosuspend | reference()
  def trigger_method(method_name, payload, timeout \\ 0)

  def trigger_method(method, req, 0) do
    Process.send(self(), Jason.encode!(Map.merge(req, %{method: method})), [])
  end

  def trigger_method(method, req, timeout) do
    Process.send_after(self(), Jason.encode!(Map.merge(req, %{method: method})), timeout)
  end
end