defmodule GenBuffer do
  @moduledoc """
  Documentation for GenBuffer.

  ## Usage

      defmodule ExdStreams.Processing.Writer do
        use GenBuffer,
          block: true,
          interval: 1000,
          limit: 10

        @impl true
        def flush(events) do
          :ok
        end

      end

  """

  defmacro __using__(opts) do
    quote bind_quoted: [opts: opts] do
      use GenServer

      @static_opts opts
      {otp_app, adapter} = GenBuffer.Config.compile_config(__MODULE__, opts)
      @otp_app otp_app
      @adapter adapter

      def __adapter__, do: @adapter

      def child_spec(opts) do
        %{
          id: __MODULE__,
          start: {__MODULE__, :start_link, [opts]},
          type: :worker
        }
      end

      ## Client

      @doc """

      """
      def start_link(opts \\ []) do
        name = Keyword.get(opts, :name, __MODULE__)
        GenServer.start_link(__MODULE__, opts, name: name)
      end

      @doc """

      """
      def add(event) when not is_list(event) do
        GenServer.call(__MODULE__, {:add, [event]})
      end
      def add(events) do
        GenServer.call(__MODULE__, {:add, events})
      end

      ## Server

      @impl true
      def init(opts) do
        limit = Keyword.fetch!(@static_opts, :limit)
        interval = Keyword.fetch!(@static_opts, :interval)

        Process.send_after(self(), :flush, interval)

        queue = :queue.new()
        state = %{
          queue: queue,
          count: 0,
          limit: limit,
          interval: interval,
          blocks: []
        }
        {:ok, state}
      end

      @impl true
      def handle_call({:add, events}, from, state) do
        blocks = state.blocks ++ [from]
        queue = Enum.reduce(events, state.queue, fn event, queue -> :queue.in(event, queue) end)
        count = state.count + length(events)
        new_state = %{state | queue: queue, count: count, blocks: blocks}

        if count >= state.limit do
          handle_info(:flush, new_state)
        else
          {:noreply, new_state}
        end
      end

      @impl true
      def handle_info(:flush, state) do
        flushed = :queue.to_list(state.queue)
        if length(flushed) > 0, do: __MODULE__.flush(flushed)
        for pid <- state.blocks, do: GenServer.reply(pid, :ok)
        Process.send_after(self(), :flush, state.interval)
        {:noreply, %{state | queue: :queue.new(), count: 0, blocks: []}}
      end

    end
  end

end