ex_github_poller

defmodule ExGithubPoller.Application do
  use Application

  def start(_type, _args) do
    IO.puts(:stderr, "starting")
    Confex.resolve_env!(:ex_github_poller)
    children = []
    Supervisor.start_link(children, strategy: :one_for_one)
  end
end

defmodule ExGithubPoller.Param do
  defstruct last_event: nil, etag: nil
end

defmodule ExGithubPoller do
  alias ExGithubPoller.Param
  alias HTTPoison.Response
  import Logger

  @spec events(any, any, any) :: any
  def events(owner, repo, param \\ %Param{}) do
    url = "https://api.github.com/repos/#{owner}/#{repo}/events"

    # TODO : needs handling for the following cases
    # 1. unauthorized/non-existent repo - status_code: 401
    # 2. rate limit exceeded - {"X-RateLimit-Limit", "60"}, {"X-RateLimit-Remaining", "0"}, {"X-RateLimit-Reset", "1559908212"} status_code: 403
    stream =
      Stream.resource(
        fn -> nil end,
        fn acc ->
          case acc do
            nil ->
              debug("#{owner}/#{repo} - start")
              data = request(url, param)
              {[data], data}

            {_, _, nil} ->
              debug("#{owner}/#{repo} - no next link")
              {:halt, nil}

            {_, _, next} ->
              # IO.puts(:stderr,"next")
              debug("#{owner}/#{repo} - next")
              data = request(next, param)
              {[data], data}

            unexpected ->
              # IO.puts(:stderr,"bad" )
              error("#{owner}/#{repo} - #{inspect(unexpected)} ")
              {:halt, nil}
          end
        end,
        fn _ -> nil end
      )

    # GOOD TO HERE...

    # require IEx ; IEx.pry()

    res = stream |> Enum.to_list() |> List.flatten()

    {_, headers, _} = hd(res)

    etag = Map.get(headers, "ETag")
    end_headers = List.last(res |> Enum.map(&elem(&1, 1)))
    limit_limit = String.to_integer(end_headers["X-RateLimit-Limit"])
    limit_remaining = String.to_integer(end_headers["X-RateLimit-Remaining"])
    limit_reset = String.to_integer(end_headers["X-RateLimit-Reset"])

    # # res2  = res |> Enum.flat_map_reduce([], fn({body,_,_},acc) ->  [body] ++ acc end)

    # {etag, res2}
    # stream |> Enum.to_list |> List.flatten
    # require IEx ; IEx.pry()
    ret = res |> Enum.map(&elem(&1, 0)) |> List.flatten()

    %{
      etag: etag,
      limit_limit: limit_limit,
      limit_remaining: limit_remaining,
      limit_reset: limit_reset,
      events: ret
    }
  end

  def filter(data, nil) do
    data
  end

  def filter({events, headers, next_link}, last_event) do
    # require IEx ; IEx.pry()

    reducer = fn event, {changed, l} = acc ->
      case changed do
        true ->
          acc

        false ->
          case String.to_integer(event["id"]) > last_event do
            true -> {false, l ++ [event]}
            false -> {true, l ++ [event]}
          end
      end
    end

    case events |> Enum.reduce({false, []}, reducer) do
      {false, events} -> {events, headers, next_link}
      {true, events} -> {events, headers, nil}
    end
  end

  @spec request(binary, ExGithubPoller.Param.t()) :: {any, map, any}
  def request(url, param) do
    # TODO - this needs to be stored in such a way it can be dynamically updated
    # TODO - provide a plugable strategy or something.
    token = Application.get_env(:ex_github_poller, :token)

    rheaders = %{
      "Authorization" => "token #{token}"
    }

    rheaders =
      case param.etag do
        nil -> rheaders
        etag -> Map.put(rheaders, "If-None-Match", etag)
      end

    case HTTPoison.get!(url, rheaders) do
      %Response{body: body, headers: headers, status_code: 200} ->
        data = JSX.decode!(body)
        headers = Map.new(headers)
        next_link = next_link(headers)
        resp = {data, headers, next_link}
        filter(resp, param.last_event)

      %Response{headers: headers, status_code: 304} ->
        {[], Map.new(headers), nil}
    end
  end

  defp next_link(%{"Link" => link}) do
    for links <- String.split(link, ",") do
      Regex.named_captures(~r/<(?<link>.*)>;\s*rel=\"(?<rel>.*)\"/, links)
      |> case do
        %{"link" => link, "rel" => "next"} -> link
        _ -> nil
      end
    end
    |> Enum.filter(&(not is_nil(&1)))
    |> List.first()
  end

  defp next_link(_), do: nil
end