defmodule ToweropsWeb.Plugs.CaptureTimezone do
  @moduledoc """
  Captures the cf-timezone header from Cloudflare and stores it in session.

  Cloudflare provides timezone detection via the cf-timezone header using
  IANA timezone database format (e.g., "America/Chicago", "Europe/London").

  Falls back to "UTC" if the header is not present (development, non-Cloudflare).
  """
  import Plug.Conn

  @doc false
  def init(opts), do: opts

  @doc false
  def call(conn, _opts) do
    timezone =
      case get_req_header(conn, "cf-timezone") do
        [tz] when is_binary(tz) and byte_size(tz) > 0 -> tz
        _ -> "UTC"
      end

    put_session(conn, :detected_timezone, timezone)
  end
end