defmodule ProdopsEx.Stream do
  @moduledoc false

  @doc """
  Creates a readable stream of information that another process can consume.

  This is used for endpoints that support returning text as it is generated,
  rather than waiting for the entire generation output to be ready.
  """
  def new(start_fun) do
    Stream.resource(
      start_fun,
      fn
        {:error, %HTTPoison.Error{} = error} ->
          {
            [
              %{
                "status" => :error,
                "reason" => error.reason
              }
            ],
            error
          }

        %HTTPoison.Error{} = error ->
          {:halt, error}

        res ->
          {res, id} =
            case res do
              {:ok, %HTTPoison.AsyncResponse{id: id} = res} ->
                {res, id}

              %HTTPoison.AsyncResponse{id: id} = res ->
                {res, id}
            end

          receive do
            %HTTPoison.AsyncStatus{id: ^id, code: code} ->
              HTTPoison.stream_next(res)

              case code do
                200 ->
                  {[], res}

                _ ->
                  {
                    [
                      %{
                        "status" => :error,
                        "code" => code,
                        "choices" => []
                      }
                    ],
                    res
                  }
              end

            %HTTPoison.AsyncHeaders{id: ^id, headers: _headers} ->
              HTTPoison.stream_next(res)
              {[], res}

            %HTTPoison.AsyncChunk{chunk: chunk} ->
              data =
                chunk
                |> String.split("\n")
                |> Enum.filter(fn line -> String.starts_with?(line, "data: ") end)
                |> Enum.map(fn line -> String.trim_leading(line, "data: ") end)

              HTTPoison.stream_next(res)
              {data, res}

            %HTTPoison.AsyncEnd{} ->
              {:halt, res}
          end
      end,
      fn %{id: id} ->
        :hackney.stop_async(id)
      end
    )
  end
end