defmodule Tesla.Middleware.OpenTelemetry do
  require OpenTelemetry.Tracer
  @behaviour Tesla.Middleware

  def call(env, next, _options) do
    span_name = get_span_name(env)

    OpenTelemetry.Tracer.with_span span_name, %{kind: :client} do
      env
      |> Tesla.put_headers(:otel_propagator_text_map.inject([]))
      |> Tesla.run(next)
      |> set_span_attributes()
      |> handle_result()
    end
  end

  defp get_span_name(env) do
    case env.opts[:path_params] do
      nil -> "HTTP #{http_method(env.method)}"
      _ -> URI.parse(env.url).path
    end
  end

  defp set_span_attributes({_, %Tesla.Env{} = env} = result) do
    OpenTelemetry.Tracer.set_attributes(build_attrs(env))

    result
  end

  defp set_span_attributes(result) do
    result
  end

  defp handle_result({:ok, %Tesla.Env{status: status} = env}) when status > 400 do
    OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, ""))

    {:ok, env}
  end

  defp handle_result({:error, {Tesla.Middleware.FollowRedirects, :too_many_redirects}} = result) do
    OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, ""))

    result
  end

  defp handle_result({:ok, env}) do
    {:ok, env}
  end

  defp handle_result(result) do
    OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, ""))

    result
  end

  defp build_attrs(%Tesla.Env{
         method: method,
         url: url,
         status: status_code,
         headers: headers,
         query: query
       }) do
    url = Tesla.build_url(url, query)
    uri = URI.parse(url)

    attrs = %{
      "http.method": http_method(method),
      "http.url": url,
      "http.target": uri.path,
      "http.host": uri.host,
      "http.scheme": uri.scheme,
      "http.status_code": status_code
    }

    maybe_append_content_length(attrs, headers)
  end

  defp maybe_append_content_length(attrs, headers) do
    case Enum.find(headers, fn {k, _v} -> k == "content-length" end) do
      nil ->
        attrs

      {_key, content_length} ->
        Map.put(attrs, :"http.response_content_length", content_length)
    end
  end

  defp http_method(method) do
    method
    |> Atom.to_string()
    |> String.upcase()
  end
end