defmodule Tamnoon.Methods do
  @moduledoc """
  Provides default implementations for methods you need to get your Tamnoon server
  working - basic state management (with `tmnn_get/2` and `tmnn_update/2`) and basic handling of
  PubSub channels (via `tmnn_sub/2`, `tmnn_unsub/2`, `tmnn_pub/2`, `tmnn_subbed_channels/2`)
  > #### Using the module {: .info}
  > When you `use Tamnoon.Methods`, every method in this module will be imported for you,
  > letting you conveniently make a _methods module_. See `m:Tamnoon.MethodManager` for
  > details on making one.

  _Note: in the documentation of the default methods, the term 'returns' is used both
  to describe the return value of the function and the value of the server's response._
  """
  defmacro __using__(_opts \\ []) do
    quote do
      import Tamnoon.MethodManager
      import Tamnoon.Methods
      def tmnn_get(req, state), do: get(req, state)
      def tmnn_update(req, state), do: update(req, state)
      def tmnn_sub(req, state), do: sub(req, state)
      def tmnn_pub(req, state), do: pub(req, state)
      def tmnn_unsub(req, state), do: unsub(req, state)
      def tmnn_subbed_channels(req, state), do: subbed_channels(req, state)
    end
  end
  @doc """
  Returns the field with the key specified under the `"key"` field
  in the request. Returns an error string if there is no such item.
  """
  @spec tmnn_get(map(), map()) :: {field :: map(), state :: map()} | {%{error: error :: String.t()}, state :: map()}
  def tmnn_get(req, state), do: get(req, state)
  @doc """
  Updates the value of the item with the key at the `"key"` field on the request,
  setting it to the value at the `"val"` key. Returns a tuple with the updated field and
  the state, or an error string if there is no such item.
  """
  @spec tmnn_update(map(), map()) :: {new_field :: map(), state :: map()} | {%{error: error :: String.t()}, state :: map()}
  def tmnn_update(req, state), do: update(req, state)
  @doc """
  Subscribes to the channel under the `"key"` field in the request. If there is no such
  channel, one will be created (with the client subscribed to it).
  If the client is already subscribed to the channel nothing will happen.
  """
  @spec tmnn_sub(map(), map()) :: {%{sub: :ok}, state :: map()}
  def tmnn_sub(req, state), do: sub(req, state)
  @doc """
  Will send the request under the `"action"` key in the request to every client
  in the channel under the `"channel"` key.
  """
  @spec tmnn_pub(map(), map()) :: {%{pub: :ok}, state :: map()}
  def tmnn_pub(req, state), do: pub(req, state)
  @doc """
  Unsubscribes from the channel under the `"key"` in the request.
  """
  @spec tmnn_unsub(map(), map()) :: {%{unsub: :ok}, state :: map()} | {%{error: error :: String.t()}, state :: map()}
  def tmnn_unsub(req, state), do: unsub(req, state)
  @doc """
  Returns a list of the channels the client is currently subscribed to.
  """
  @spec tmnn_subbed_channels(map(), map()) :: {%{subbed_channels: channels :: [String.t()]}, state :: map()}
  def tmnn_subbed_channels(req, state), do: subbed_channels(req, state)

  @doc false
  def get(req, state) do
    key = get_key(req, state)
    if (key != nil) do
      {%{key => state[key]}, state}
    else
      {%{error: "Error: no matching key"}, state}
    end
  end

  @doc false
  def update(req, state) do
    key = get_key(req, state)
    if (key != nil) do
      {%{key => req["val"]}, Map.put(state, key, req["val"])}
    else
      {%{error: "Error: no matching key"}, state}
    end
  end

  @doc false
  def sub(req, state) do
    if (!is_subbed?(req["key"])) do
      Tamnoon.Registry
      |> Registry.register(req["key"], {})
    end
    {%{sub: :ok}, state}
  end

  @doc false
  def unsub(req, state) do
    cond do
      req["key"] == "clients" -> {%{error: "Error: can't unsub from clients channel"}, state}
      is_subbed?(req["key"]) ->
        Tamnoon.Registry
        |> Registry.unregister(req["key"])
        {%{unsub: :ok}, state}
      true -> {%{unsub: :ok}, state}
    end
  end

  @doc false
  def subbed_channels(_req, state) do
    channels = Tamnoon.Registry
    |> Registry.keys(self())
    {%{subbed_channels: channels}, state}
  end

  @doc false
  def pub(req, state) do
    Tamnoon.Registry
    |> Registry.dispatch(req["channel"], fn entries ->
      for {pid, _} <- entries do
        Process.send(pid, elem(Jason.encode(req["action"]), 1), [])
      end
    end)
    {%{pub: :ok}, state}
  end

  @doc """
  Returns the value of the key under the field `"key"` in the request as an atom.
  Note: this is *NOT* a method handler - simply a utility function.
  """
  @spec get_key(map(), map()) :: atom() | nil
  def get_key(req, state) do
    cond do
      Map.has_key?(state, req["key"]) -> req["key"]
      Map.has_key?(state, String.to_atom(req["key"])) -> String.to_atom(req["key"])
      true -> nil
    end
  end

  defp is_subbed?(key) do
    Tamnoon.Registry
    |> Registry.lookup(key)
    |> Enum.any?(fn {pid, _} -> pid == self() end)
  end
end