defmodule Pollin.Backend.Memory.EndpointWorker do
  @moduledoc """
  Worker for endpoint
  """

  use GenServer
  alias Pollin.Resource.Endpoint
  alias Pollin.Backend.Memory.{CallbackWorker, EndpointSupervisor}

  @doc false
  def start_link,
    do: GenServer.start_link(__MODULE__, [], name: __MODULE__)

  @doc false
  def init(_opts) do
    Process.flag(:trap_exit, true)
    {:ok, Application.get_env(:pollin, :endpoints) || []}
  end

  ## Public API

  @doc """
  List all endpoint
  """
  def index,
    do: GenServer.call(__MODULE__, {:index})

  @doc """
  Find endpoint
  """
  def find(id),
    do: GenServer.call(__MODULE__, {:find, id})

  @doc """
  Create an endpoint
  """
  def create(%Endpoint{} = endpoint) do
    GenServer.call(__MODULE__, {:create, endpoint})
    EndpointSupervisor.start_callback_worker(:"#{endpoint.id}")
  end

  @doc """
  Delete an endpoint
  """
  def delete(id),
    do: GenServer.cast(__MODULE__, {:delete, id})

  @doc """
  Update an endpoint
  """
  def update(%Endpoint{} = endpoint),
    do: GenServer.cast(__MODULE__, {:update, endpoint})

  ## Private API

  @doc false
  def handle_call({:index}, _from, state) do
    items =
      state
      |> Enum.map(fn {_key, endpoint} -> endpoint end)

    {:reply, items, state}
  end

  @doc false
  def handle_call({:create, endpoint}, _from, state),
    do: {:reply, :ok, List.insert_at(state, -1, {endpoint.id, endpoint})}

  @doc false
  def handle_call({:find, id}, _from, state) do
    endpoint =
      case List.keyfind(state, id, 0) do
        {_, endpoint} -> endpoint
        nil -> nil
      end
    {:reply, endpoint, state}
  end

  @doc false
  def handle_cast({:delete, id}, state) do
    id = String.to_atom(id)
    CallbackWorker.reset(id)
    Supervisor.terminate_child(EndpointSupervisor, id)
    Supervisor.delete_child(EndpointSupervisor, id)
    {:noreply, List.keydelete(state, "#{id}", 0)}
  end

  @doc false
  def handle_cast({:update, endpoint}, state) do
    CallbackWorker.update_endpoint(endpoint)
    {:noreply, List.keyreplace(state, endpoint.id, 0, {endpoint.id, endpoint})}
  end

  @doc false
  def handle_info({:EXIT, _pid, reason}, state),
    do: {:stop, reason, state}

  @doc false
  def terminate(_reason, state) do
    Application.put_env(:pollin, :endpoints, state)
    :ok
  end
end