defmodule PlanB.EventBus do
    use GenServer

    @moduledoc """
    ## Module EventBus

    This module is created as a GenServer. To use it just call start_link/1, then create a channel and register subscribers to it.
    """

    # Server side
    @spec init(any) :: {:ok, any}
    def init(state) do
        {:ok, state}
    end

    def handle_call({:lookup, name}, _from, state) when is_binary(name) do
        state
        |> Map.fetch(name)
        |> case do
            :error -> {:reply, :fail, state}
            {:ok, modules} ->
                results =
                    modules
                    |> Enum.map(fn (module) -> {module, Process.whereis(module) } end)

                {:reply, {name, results}, state}
        end
    end

    def handle_call({:register, {name, module}}, _from, state) do
        state
        |> Map.fetch(name)
        |> case do
            :error ->
                new_state = state |> Map.put(name, [ module ])
                {:reply, :ok, new_state}
            {:ok, modules} ->
                modules
                |> Enum.member?(module)
                |> case do
                    true -> {:reply, :ok, state}
                    false ->
                        new_state = state |> Map.put(name, modules ++ [module])
                        {:reply, :ok, new_state}
                end
        end
    end

    def handle_cast({:publish, name, payload}, state) do
        state
        |> Map.fetch(name)
        |> case do
            :error -> {:noreply, state}
            {:ok, modules} ->
                modules
                |> Enum.each(fn (module) -> GenServer.cast(module, payload) end)
                {:noreply, state}
        end
    end

    # Client side
    @doc """
    ### start_link/1
    """
    @spec start_link(any) :: :ignore | {:error, any} | {:ok, pid}
    def start_link([state] = args) when is_list(args) and is_map(state) do
        GenServer.start_link __MODULE__, state, name: __MODULE__
    end

    @doc """
    ### stop_server/0
    """
    @spec stop_server :: :ok
    def stop_server, do: GenServer.stop __MODULE__

    @doc """
    ### health_check/0
    """
    @spec health_check :: :fail | :ok
    def health_check do
        case GenServer.whereis(__MODULE__) do
            pid when is_pid(pid) -> :ok
            _ -> :fail
        end
    end

    @doc """
    ### register/2
    """
    @spec register(binary, Module) :: any
    def register(name, module), do: GenServer.call __MODULE__, {:register, {name, module}}

    @doc """
    ### lookup/1
    """
    @spec lookup(binary) :: any
    def lookup(name) when is_binary(name), do: GenServer.call __MODULE__, {:lookup, name}

    @doc """
    ### publish/2
    """
    @spec publish(binary, any) :: any
    def publish(name, payload) when is_binary(name), do: GenServer.cast __MODULE__, {:publish, name, payload}
end